WO2025219513A1

WO2025219513A1 - Compositions and processes for removing heavy metals from acid-containing streams

Info

Publication number: WO2025219513A1
Application number: PCT/EP2025/060636
Authority: WO
Inventors: Ravi Rajshekar HIREMATH; Lei Zhang
Original assignee: Cytec Industries Inc
Current assignee: Cytec Industries Inc
Priority date: 2024-04-19
Filing date: 2025-04-17
Publication date: 2025-10-23
Anticipated expiration: 2026-10-19

Abstract

Compositions and processes for removing/recovering heavy metal ions from an acid-containing streams by adding reagents having at least one dialkyldithiophosphate compound, with the alkyl chain length of C2 to C12, at least one at least one phosphonate compound, optionally at least one dialkyldithiophosphinate compound, and optionally at least one surfactant to an acid-containing stream to form heavy metal ion complexes, and separating the heavy metal ion complexes from the acid-containing stream are provided herein.

Description

COMPOSITIONS AND PROCESSES FOR REMOVING HEAVY METALS FROM ACID-CONTAINING STREAMS Field of the Invention The technological concept disclosed herein generally relates to purification of industrial process streams. More particularly, the concept disclosed herein relates to removing heavy metal ions, especially cadmium, arsenic and copper, from acid-containing streams. Background In several sectors, industries are faced with metal impurities which, beyond a certain level, are considered unacceptable, depending on industry specification. Accordingly, the metal impurities have to be either completely removed or their levels have to be significantly reduced. It is therefore necessary to set up purification of industrial process streams, and in particular acid-containing streams, as for example oxyacid containing streams like phosphoric acid, sulfuric acid and acidic metal sulfate containing streams. This is notably the case during the production of phosphoric acid, where certain metal impurities in the form of heavy metal ions, such as cadmium (Cd), arsenic (As), lead (Pb), copper (Cu), and mercury (Hg), are present as minerals in the phosphate rock and are dissolved into the phosphoric acid. For example, cadmium (Cd) is toxic and can cause multiple health issues to human. Studies show that the major exposure of Cd to nonsmoking general population is through ingestion of contaminated food. Phosphate fertilizers have been identified as an important source that introduces Cd to the soil, which can be easily absorbed by agricultural plants and accumulated into the food chain (“Cadmium in phosphate fertilizers; ecological and economical aspects”, CHEMIK 2014, 68, 10, 837–842). Cd in phosphate fertilizer comes from phosphoric acid, the major raw material used to produce phosphate fertilizer. In fact, the majority of phosphoric acid production is used to produce fertilizer. Cd in phosphoric acid further stems from the phosphate bearing ores. Therefore, Cd can be removed either from the phosphate ore or from the phosphoric acid stream, with the latter being the focus of research in the past decades. Several scientific publications (“Cadmium(II) extraction from phosphoric media by bis(2,4,4-trimethylpentyl) thiophosphinic acid (Cyanex 302),” Fluid Phase Equilibria 145 (1998) 301-310), and “Extraction of cadmium from phosphoric acid by trioctylphosphine oxide/kerosene solvent using factorial design,” Periodica Polytechnic Chemical Engineering 55/2 (2011) 45–48)) discuss removal of Cadmium from phosphoric acid based on solvent extraction method using reagents such as bis(2,4,4-trimethylpentyl) thiophosphinic acid/kerosene, and trioctylphosphine oxide/kerosene, respectively. Likewise, during the hydrometallurgical production of cobalt and nickel metals, certain metal impurities, including cadmium, are often present in the solid feed material (e.g. ore, concentrate, electronic waste (e-waste)). Cobalt and nickel metals are extracted from the solid feed material through leaching, that involves transferring a metal of interest from naturally occurring minerals into an aqueous solution, where cobalt and nickel metals may be first subjected to comminution and then contacted with a sulfuric acid leaching reagent which dissolves the metal, transferring it to an aqueous phase as a metal sulfate. Cobalt and nickel, considered “value metals”, and metal impurities are transferred from the solid feed material to the aqueous phase in varying quantities forming an acidic metal sulfate containing stream. Value metals may be recovered from the aqueous solution as saleable products in subsequent product recovery steps by techniques such as precipitation, electrowinning, or crystallization. For example, cadmium levels in cobalt sulfate heptahydrate and nickel sulfate hexahydrate, produced for the lithium ion battery industry, may be ≤ 5 mg/kg and ≤ 1 mg/kg respectively. Nickel power may require cadmium levels ≤ 7 mg/kg. Impurity metal ions in the acidic metal sulfate stream must be reduced with high efficiency and with high selectivity relative to value metals. Iron, aluminum, manganese, and/or copper present in the initial acidic metal sulfate leach solution are commonly removed using precipitation in a multi-stage process by the addition of lime (or an alternative base) and an oxidant such as air, sulfur dioxide or their mixture. Copper may be further reduced using conventional methods such as solvent extraction and/or ion exchange. Minor impurity metal ions, especially cadmium, and also arsenic, lead, mercury, chromium, titanium, and copper may require alternative processing steps to reduce their concentration in the acidic metal sulfate-containing streams. Therefore, several categories of technologies to remove Cd from acid streams have been developed, including co-crystallization with anhydrite, precipitation with sulfide ions, hydroxides, carbonates, and organic sulfurous compounds, cementation, removal by solvent extraction, removal by ion exchange, removal by adsorbents, and separation by membrane technology ((“Progress in the development of decadmiation of phosphorus fertilizers” Fertilizer Industry Federation of Australia, Inc., Conference “Fertilizers in Focus”, 2001, 101-106; (Rao, K.S., Mohapatra, M., Anand, S.,Venkateswarlu, P. (2010), Review on cadmium removal from aqueous solutions. International Journal of Engineering, Science and Technology.2(7)). U.S. Patent No. 4,378,340 (1983) describes a method of removing heavy metals, particularly cadmium, from wet process phosphoric acid through partial neutralization of acids with alkali, followed by precipitation with sulfide compounds. U.S. Patent No. 5,431,895 (1995) also discloses using alkali solution and aqueous sulfide solution simultaneously with thorough mixing to remove lead and cadmium from phosphoric acid. The precipitation of metal hydroxides and carbonates is complicated by poor selectivity resulting in the co-precipitation of value metals. The precipitation of cadmium sulfide involves the use of hazardous sulfide precipitating agents (Na₂S, NaHS, H₂S). Alternative cadmium precipitation methods were proposed by Rickelton (1998) who found a selective method of removing cadmium from zinc, cobalt and nickel by precipitation as its diisobutyldithiophosphinate complex. Dialkyldithiophinates are synthesized using high- pressure phosphine and may be difficult to manufacture industrially. The patent application DE 40 40474 A1 (1990) discloses using dithiophosphorous esters of the formula (R- (OC2H4)x-O)2PS2M where R is C9-C18 alkyl or alkenyl compound, x is an integer from 0 to 6 and M is a cation to remove Zn, Cd, Hg, Cu, Ni or As from crude phosphoric acid or from sulfuric acid (for example, during the treatment of lead-acid batteries). Cadmium is removed using precipitation and flotation in the presence of a foaming agent. Solvent extraction (liquid-liquid) extraction with dithiophosphorous compounds has also been proposed to extract cadmium from phosphoric acid and sulfuric acid based systems. U.S. Patent No. 4,479,924 (1980) proposes a method of extracting metal ions, including cadmium, from an aqueous solution by contact with a reagent mixture including a water insoluble diester of dithiophosphoric acid, a water-insoluble phosphate, and a diluent. Heavy metal contamination of food, especially cadmium that stems from use of phosphoric acid in fertilizer production, continues to be a concern to public health.. Additionally, there has been a recent regulatory push to further limit the Cd level in phosphate fertilizers (See European Commission Fact Sheet. “Circular economy: New Regulation to boost the use of organic and waste-based fertilisers.” EU MEMO-16-826, 17 March 2016, europa.eu/rapid/press-release_MEMO-16-826_en.htm). Thus, while the various reagents and approaches discussed above may have some merits and applicability in acid-containing streams, new and improved compositions and methods are still needed in industry to remove heavy metal ions, especially cadmium or arsenic, from acid-containing streams with high efficiency, low capital costs, and low reagent usage for improving their wide acceptance in industry. The economic impact for the issue of heavy metal is substantial, and the industry is in need of a more efficient and economical technology than that which currently exists. However, despite these efforts, there remains an important issue that these different solutions do not resolve. Accordingly, the compositions and methods presently available for heavy metal removal from acid streams in the production process require further and/or continuous improvement. Since many factors (e.g., ore type, temperature, agitation, reactor design, acid chemistry, foreign ions, organic species, and viscosity of acid medium) can affect the performance of reagents, it is a great challenge to develop high-efficiency reagents useful for removing heavy metals from acid streams. Successful reagents for removing heavy metals in industrial process streams such as wet process phosphoric acid or hydrometallurgical production of cobalt, and nickel metals would be a useful advance in the art and could find rapid acceptance in the industry. Summary The foregoing and additional objects are attained in accordance with the principles of the invention wherein the inventors detail the discovery that at least one dialkyldithiophosphate compound, with the alkyl chain length of C2 to C12 and at least one phosphonate compound, and optionally with at least one surfactant and/or at least one dialkyldithiophosphinate compound, are effective as a new reagent composition for removing heavy metal ions from acid-containing streams. Accordingly, the processes for removing heavy metal ions according to various embodiments of the present invention as described herein below are applicable for use in purification of industrial process streams. Accordingly, in one aspect the present invention provides compositions for complexing heavy metals ions, especially cadmium and arsenic, from the acid-containing streams, wherein the composition comprises an effective amount of a reagent comprising at least one dialkyldithiophosphate compound, with the alkyl chain length of C2 to C12 and at least one phosphonate compound. In the same or additional embodiments, the reagent can further comprise at least one surfactant. In the same or additional embodiments, the reagent can further comprise at least one dialkyldithiophosphinate compound. In another aspect, the invention provides processes for removing heavy metal ions, especially cadmium and arsenic, from a solution containing acid streams, by adding an effective amount of a reagent comprising at least one dialkyldithiophosphate compound, with the alkyl chain length of C2 to C12 and at least one phosphonate compound to the solution to form heavy metal complexes and separating the heavy metal complexes from the solution. In the same or additional embodiments, the process can further comprise adding an effective amount of at least one surfactant to the solution containing acid streams. In the same or additional embodiments, the process can further comprise adding an effective amount of at least one dialkyldithiophosphinate compound to the solution containing acid streams. In the same or additional embodiments, the process can further comprise adding an effective amount of a reducing agent to the solution containing acid streams. In the same or additional embodiments, the process can further comprise adding an effective amount of an adsorbent to the solution containing acid streams. This summary of the invention does not list all necessary characteristics and, therefore, subcombinations of these characteristics or elements may also constitute an invention. Accordingly, these and other objects, features and advantages of this invention will become apparent from the following detailed description of the various aspects of the invention taken in conjunction with the accompanying Figures and Examples. Detailed Description The present disclosure generally relates to purification of solutions in industrial process streams. More particularly, the inventors describe herein reagents and processes for removing and/or recovering heavy metal ions from acid-containing streams by adding an effective amount at least one dialkyldithiophosphate compound with the alkyl chain length of C2 to C12, and at least one phosphonate compound to form a heavy metal complex, and separating the complex from the solution. The compositions and processes described herein provide improvement and/or an unexpected advantage when compared to compositions and processes of the prior art. As employed throughout the present disclosure, the following terms are provided to assist the reader. Unless otherwise defined, all terms of art, notations and other scientific or industrial terms or terminology used herein are intended to have the meanings commonly understood by those of skill in the chemical and/or phosphoric acid production arts. In some cases, terms with commonly understood meanings are defined herein for clarity and/or for ready reference, and the inclusion of such definitions herein should not necessarily be construed to represent a substantial difference over the definition of the term as generally understood in the art unless otherwise indicated. As used herein and in the appended claims, the singular forms include plural referents unless the context clearly dictates otherwise. Throughout this specification, the terms retain their definitions. As used herein with reference to the present invention, the term “heavy metal” or “metal” shall refer to those elements of the periodic table having a density of more than 5 g/cm³ and/or requiring a reduced concentration in the value metal product relative to the feed solution, and an oxidation state higher than 0, (i.e., heavy metal ions). Such heavy metal ions include, for example, one or more of, cadmium, chromium, arsenic, nickel, mercury, zinc, manganese, titanium, copper and lead. In any or all embodiments, cadmium ions are removed from acid-containing streams. In the same or alternate embodiments, arsenic ions are removed from acid-containing streams. The concept of “heavy metal complex” refers to compounds formed by reacting heavy metal ions with chelating agents. Heavy metal complexes can be solid, waxy, or oily in the phosphoric acid solutions. They can precipitate, float, or suspend in the phosphoric acid solutions. Those skilled in the art will understand that reference to “acid-containing streams”, or “acid solutions,” or “solutions containing acid,” in the context of the invention includes any acidic solution. In the present invention, the acid-containing streams can be oxyacid containing streams like phosphoric acid, sulfuric acid and acidic metal sulfate containing streams. According to the present invention, the acid-containing streams can be phosphoric acid containing streams that, in the context of the invention, may include any acidic solution containing crude phosphoric acid, digestion slurries of phosphoric acid, filtered phosphoric acid, and/or concentrated phosphoric acid. Such phosphoric acid containing streams are typically obtained from industrial phosphoric acid production plant streams. According to the present invention, the acid-containing streams can also be acidic metal sulfate containing streams that; in the context of the invention, may include any acidic solution derived from the leaching of a solid feed material with sulfuric acid. Such metal sulfate containing streams are typically obtained from plant streams of hydrometallurgical production of cobalt, and nickel metals. Generally, acidic metal sulfate streams can contain cobalt and/or nickel metals. “Effective amount” means the dosage of any reagents on an active basis (such as the compositions comprising at least one dialkyldithiophosphate compound with the alkyl chain length of C2 to C12 and at least one phosphonate compound described herein) necessary to provide the desired performance in the acid system or circuit being treated (such as the formation of heavy metal complexes) when compared to an untreated control system or system using a reagent product of the prior art. As used herein, the term “alkyl” is intended to include linear, branched, or cyclic hydrocarbon structures and combinations thereof. Preferred alkyl groups are those of C30 or below. Lower alkyl refers to alkyl groups of from 1 to 6 carbon atoms. Examples of lower alkyl groups include methyl, ethyl, propyl, isopropyl, butyl, s-and t-butyl, pentyl, hexyl and the like. Cycloalkyl is a subset of alkyl and includes cyclic hydrocarbon groups having from 3 to 30 carbon atoms, preferably from 3 to 8 carbon atoms as well as polycyclic hydrocarbons having 7 to 10 carbon atoms. The term "aryl" as used herein refers to cyclic aromatic hydrocarbons that do not contain heteroatoms in the ring. In any or all embodiments, aryl groups contain about 6 to about 14 carbons in the ring portions of the groups. Thus, aryl groups include, but are not limited to, phenyl, azulenyl, heptalenyl, biphenyl, indacenyl, fluorenyl, phenanthrenyl, triphenylenyl, pyrenyl, naphthacenyl, chrysenyl, biphenylenyl, anthracenyl, and naphthyl groups. Aryl groups can be unsubstituted or substituted, as defined herein. Representative substituted aryl groups can be mono-substituted or substituted more than once, such as, but not limited to, 2-, 3-, 4-, 5-, or 6-substituted phenyl or 2-8 substituted naphthyl groups, which can be substituted with carbon or non-carbon groups such as those known to persons of skill in the art. Aryl groups of C₆-C₁₂ are preferred. The term “alkaryl” as used herein is a broad term and is used in its ordinary sense, including, without limitation, to refer to an aryl having at least one aryl hydrogen atom replaced with an alkyl moiety. The term “aralkyl” as used herein is a broad term and is used in its ordinary sense, including, without limitation, to refer to an alkyl having at least one alkyl hydrogen atom replaced with an aryl moiety, such as benzyl, –CH2(1 or 2- naphthyl), –(CH2)2phenyl, –(CH2)3phenyl, –CH(phenyl)2, and the like. Particularly preferred are C_7-20 aralkyl groups. The terms “comprised of,” “comprising,” or “comprises” as used herein includes embodiments “consisting essentially of” or “consisting of” the listed elements, and the terms “including” or “having” in context of describing the invention should be equated with “comprising”. Those skilled in the art will appreciate that while preferred embodiments are discussed in more detail below, multiple embodiments of the reagent system and processes described herein are contemplated as being within the scope of the present invention. Thus, it should be noted that any feature described with respect to one aspect or one embodiment of the invention is interchangeable and/or combinable with another aspect or embodiment of the invention unless otherwise stated. It will also be understood by those skilled in the art that any description of the invention, even though described in relation to a specific embodiment or drawing, is applicable to and interchangeable with other embodiments of the invention. Furthermore, for purposes of describing the present invention, where an element, component, or feature is said to be included in and/or selected from a list of recited elements, components, or features, those skilled in the art will appreciate that in the related embodiments of the invention described herein, the element, component, or feature can also be any one of the individual recited elements, components, or features, or can also be selected from a group consisting of any two or more of the explicitly listed elements, components, or features. Additionally, any element, component, or feature recited in such a list may also be omitted from such list. Those skilled in the art will further understand that any recitation herein of a numerical range by endpoints includes all numbers subsumed within the recited range (including fractions), whether explicitly recited or not, as well as the endpoints of the range and equivalents. The term “et seq.” is sometimes used to denote the numbers subsumed within the recited range without explicitly reciting all the numbers, and should be considered a full disclosure of all the numbers in the range. Disclosure of a narrower range or more specific group in addition to a broader range or larger group is not a disclaimer of the broader range or larger group. Accordingly, in one aspect, the invention embodies compositions for forming complexes with heavy metal ions in an acid-containing stream, wherein the compositions comprise an effective amount of a reagent comprising: at least one dialkyldithiophosphate compound with the alkyl chain length of C2 to C12; and at least one phosphonate compound. The dialkyldithiophosphate compounds with the alkyl chain length of C2 to C12, described herein for any or all embodiments, comprise dialkyldithiophosphoric acid with the alkyl chain length of C2 to C12 and any salts (e.g., calcium, magnesium, potassium, sodium, ammonium salt with the formula NR1R2R3R4⁺, where R1, R2, R3, R4 are, equal to or different from each other, independently chosen from hydrogen, alkyl or aryl groups) of any of the foregoing dialkyldithiophosphoric acid with the alkyl chain length of C2 to C12; and mixtures thereof. In the same or other embodiments, the dialkyldithiophosphate compound with the alkyl chain length of C2 to C12 is selected from the group consisting of dialkyldithiophosphoric acid with the alkyl chain length of C2 to C12 and salts of any of the foregoing dialkyldithiophosphoric acid with the alkyl chain length of C2 to C12 in the form of calcium, magnesium, potassium, sodium salt or ammonium salt with the formula NR₁R₂R₃R₄ ⁺, where R₁, R₂, R₃, R₄ are, equal to or different from each other, independently chosen from hydrogen, alkyl or aryl groups; and mixtures thereof. In some embodiments, the alkyl chain of the dialkyldithiophosphate compound according to the invention is a C6 to C12 chain. In some preferred embodiments, the alkyl chain of the dialkyldithiophosphate compound according to the invention is a C8 to C10 chain. Preferably, the alkyl chain of the dialkyldithiophosphate compound according to the invention is a C8 alkyl chain. In the same or alternate embodiments, the dialkyldithiophosphate compound is selected from the group consisting of any salts of di(1,3-dimethylbutyl) dithiophosphoric acid, di(2-ethylhexyl) dithiophosphoric acid, di(3,7-dimethyloctyl) dithiophosphoric acid, di(2-butyloctanol) dithiophosphoric acid; and mixtures thereof, said salts being as defined previously. In a preferred embodiment, dialkyldithiophosphate compound is salts of di(2- ethylhexyl) dithiophosphoric acid, di(3,7-dimethyloctyl) dithiophosphoric acid, and di(2- butyloctanol) dithiophosphoric acid, and mixtures thereof. In a more preferred embodiment, the dialkyldithiophosphate compound is any salts of di(2-ethylhexyl) dithiophosphoric acid. In a specific preferred embodiment, the dialkyldithiophosphate compound is ammonium salt of di(2-ethylhexyl) dithiophosphoric acid. In a specific preferred embodiment, the dialkyldithiophosphate compound is sodium salt of di(2- ethylhexyl) dithiophosphoric acid. In the same or alternate embodiments, the dialkyldithiophosphate compound is selected from the group consisting of di(1,3-dimethylbutyl) dithiophosphate, di(2- ethylhexyl) dithiophosphate, di(3,7-dimethyloctyl) dithiophosphate, di(2-butyloctanol) dithiophosphate; and mixtures thereof. In a preferred embodiment, dialkyldithiophosphate compound are di(2-ethylhexyl) dithiophosphate, di(3,7-dimethyloctyl) dithiophosphate, and di(2-butyloctanol) dithiophosphate; and mixtures thereof. In a more preferred embodiment, the dialkyldithiophosphate compound is di(2-ethylhexyl) dithiophosphate. In a specific preferred embodiment, the dialkyldithiophosphate compound is ammonium di(2- ethylhexyl) dithiophosphate. In a specific preferred embodiment, the dialkyldithiophosphate compound is sodium di(2-ethylhexyl) dithiophosphate. The phosphonate compounds described herein for any or all embodiments comprises the following formula: wherein: R” is an optionally substituted hydrocarbyl radical comprising from about 1 to about 20 carbons; R’ is H, optionally substituted C1-C20 alkyl, optionally substituted C6-C12 aryl, optionally substituted C7-C20 aralkyl, optionally substituted C2-C20 alkenyl, Group I metal ion, Group II metal ion, or NR₁R₂R₃R₄ ⁺, where R₁, R₂, R₃, R₄ are, equal to or different from each other, independently chosen from hydrogen, alkyl, alkenyl, or aryl groups. In the same or alternate embodiments, the phosphate compound is selected from diethylenetriaminepentakis(methylphosphonic acid), nitrilotri(methylphosphonic acid), iminodi(methylphosphonic acid), (aminomethyl)phosphonic acid, N,N- bis(phosphonomethyl)glycine, glyphosate, and mixtures thereof. In a preferred embodiment, the phosphate compound is diethylenetriaminepentakis(methylphosphonic acid). In any of the foregoing or additional embodiments of the composition, the reagent can further comprise at least one surfactant. In any of the foregoing or additional embodiments of the composition, the reagent can further comprise at least one dialkyldithiophosphinate compound. The dialkyldithiophosphinate compound described herein for any or all embodiments comprise dialkyldithiophosphinic acid and any salts (e.g., calcium, magnesium, potassium, sodium, ammonium salt with the formula NR1R2R3R4⁺, where R1, R2, R3, R4 are, equal to or different from each other, independently chosen from hydrogen, alkyl or aryl groups) of the foregoing dialkyldithiophosphinic acid; and mixtures thereof. In the same of other embodiments, the dialkyldithiophosphinate compound is selected from the group consisting of dialkydithiophosphinic acid and any salts (e.g., calcium, magnesium, potassium, sodium) of the foregoing dialkyldithiophosphinic acid in the form of calcium, magnesium, potassium, sodium salt or ammonium salt with the formula NR1R2R3R4⁺, where R1, R2, R3, R4 are, equal to or different from each other, independently chosen from hydrogen, alkyl or aryl groups; and mixtures thereof. In the same or alternate embodiments, the dialkyldithiophosphinate compound is selected from the group consisting of any salts of diisobutyl dithiophosphinic acid; bis(2,4,4-trimethylpentyl) dithiophosphinic acid; and mixtures thereof, said salts being as defined above. In a preferred embodiment, the dialkyldithiophosphinate compound is sodium diisobutyl dithiophosphinate. In any of the foregoing or additional embodiments, the surfactant compound can be selected from the group consisting of sulfosuccinates; aryl sulfonates; alkaryl sulfonates; diphenyl sulfonates; olefin sulfonates; sulfonates of ethoxylated alcohols; petroleum sulfonates; sulfosuccinamates; alkoxylated surfactants; ester/amide surfactants; EO/PO block copolymers (ethylene oxide/propylene oxide); and mixtures thereof. In the same or alternate embodiment, the surfactant can be an alkaryl sulfonates. In a preferred embodiment, the surfactant can be alkyldiphenyloxide disulfonate. Suitable alkyldiphenyloxide disulfonate compounds include, but are not limited to, DOWFAX® 2A1, DOWFAX® 3B2, DOWFAX® 8390 available from Dow Chemical. In the same or alternate embodiment, the surfactant can be a sulfosuccinate. Suitable sulfosuccinate can be sodium dioctylsulfosuccinate. Suitable sodium dioctylsulfosuccinate compounds include, but are not limited to, AEROSOL® OT-70 PG available from Syensqo S.A. In the same or alternate embodiment, the surfactant can be an alkoxylated surfactant. Suitable alkoxylated surfactants can include, but are not limited to, polyethyleneglycol sorbitan monooleate (such as TWEEN® 80 available from Croda), and polyethyleneglycol sorbitol hexaoleate (such as ATLAS® G1086 available from Croda). In another aspect, the invention embodies processes for removing heavy metal ions from an acid-containing stream, wherein such processes comprise: adding an effective amount of a reagent, comprising a composition for forming complexes with heavy metal ions as disclosed and embodied herein, to the acid-containing stream to form heavy metal ion complexes, and separating the heavy metal ion complexes from the acid-containing stream. According to one or more embodiments, the dialkyldithiophosphate compound is in a diluted solution when it is added to an acid-containing stream. For example, the diluted solution may include a percent active (of dialkyldithiophosphate compound) having a lower limit of any of greater than 0, 1, 2, 5, or 10% to an upper limit of any of 10, 12, 15, 20 or 35%. The diluted solution may include water. According to one or more embodiments, prior to adding a dialkyldithiophosphate compound to an acid-containing stream for forming heavy metal ion complexes, the dialkyldithiophosphate compound may be diluted. In any or all embodiments of the invention, the at least one dialkyldithiophosphate compound with the alkyl chain length of C2 to C12, and the at least one phosphonate compound, and optionally the at least one surfactant and/or the at least one dialkyldithiophosphinate compound, can be added to the acid-containing stream to complex the heavy metal ions. Afterwards, heavy metal complexes formed can be separated from the acid-containing stream. According to one or more embodiments, the acid-containing stream being phosphoric acid stream, the at least one dialkyldithiophosphate compound with the alkyl chain length of C2 to C12, and the at least one phosphonate compound, and optionally the at least one surfactant and/or the at least one dialkyldithiophosphinate compound, can be added to either the crude phosphoric acid or digestion slurries prior to gypsum filtration, or to the filtered phosphoric acid or to the concentrated phosphoric acid to complex the heavy metal ions. Afterwards, heavy metal complexes so formed can be separated from the phosphoric acid or slurry. According to one or more embodiments, the acid-containing stream being acidic metal sulfate stream, the at least one dialkyldithiophosphate compound with the alkyl chain length of C2 to C12, and the at least one phosphonate compound, and optionally the at least one surfactant and/or the at least one dialkyldithiophosphinate compound, can be added to the acidic metal sulfate containing solution, preferably following the removal of some other metals considering as major impurities, such as iron and copper impurities, using conventional techniques, or any point prior to the recovery of cobalt and/or nickel products. Afterwards, the heavy metal complexes so formed may be separated from the cobalt and/or nickel containing solution. Separation may be carried out via any suitable method known in the art for such separation. In any or all embodiments, the methods of separation include, but are not limited to, filtration, centrifugation, sedimentation, creaming, skimming, flocculation, adsorption, phase separation, and/or flotation. In any or all embodiments of the invention, the at least one dialkyldithiophosphate compound with the alkyl chain length of C2 to C12, and the at least one phosphonate compound, and optionally the at least one surfactant and/or the at least one dialkyldithiophosphinate compound, can be added to the solution containing acid all in one stage or added in several stages. In the same or other embodiments, the at least one dialkyldithiophosphate compound with the alkyl chain length of C2 to C12 and the at least one phosphonate compound, and optionally the at least one surfactant and/or the at least one dialkyldithiophosphinate compound, is added as a blend, or separately in any order such as concurrently together or sequentially. In a preferred embodiment, the at least one dialkyldithiophosphate compound with the alkyl chain length of C2 to C12 and the at least one phosphonate compound, and optionally the at least one surfactant and/or the at least one dialkyldithiophosphinate compound, is added as a blend. Treatment times in any or all embodiments of the invention can be from a few seconds (i.e., 5 to 10 seconds) to 240 minutes. In those instances where the reagent complexes the heavy metals very rapidly, the preferred treatment times are from about 5 seconds to 5 minutes. Most typically, the treatment times are from 10 seconds to 60 seconds or 120 seconds. The dosage of the reagent for complexing heavy metals and removal efficiency for the various heavy metals will depend on the amount of heavy metal impurities present in the ore and/or acid-containing streams. Generally, the greater the number of heavy metals present and the higher their concentrations, the greater will be the overall dosage of the reagent. Those skilled in the art will be able to readily determine and establish the optimum dosage of at least one dialkyldithiophosphate compound with the alkyl chain length of C2 to C12 and the at least one phosphonate compound, and optionally the at least one surfactant and/or the at least one dialkyldithiophosphinate compound, required using no more than routine experimentation. According to one or more embodiments, the acid-containing stream being phosphoric acid stream, the dosages may generally be in the range of from 0.01 to 50 kg (e.g., 0.01, 0.02, 0.03, 0.04, 0.05, et seq. to 0.10, 0.15, 0.20, 0.25, 0.30, et seq. to 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, 5.0, et seq. to 10, 15, 20, 25, 30, 35, 40, 45, 50 kg) reagent per ton of P2O5 of the phosphoric acid solution, based on the type of heavy metal ions to be removed. Most typically, the dosages can be from 0.1 kg to 10 kg (e.g., 0.10, 0.15, 0.20, 0.25, 0.30, et seq. to 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, 5.0, 5.5, 6.0, 6.5, 7.0, 7.5, 8.0, 8.5, 9.0, 9.5, and 10 kg) of reagent per ton of P2O5. It will be understood by those ordinary skilled in the art that any of the recited dosages (except the lowest dosage point) can also be recited as “less than” a particular dosage, e.g., less than 50 kg; or that any of the recited dosages (except the highest dosage point) can also be recited as “greater than” a particular dosage, e.g., greater than 0.10 kg. According to one or more embodiments, the acid-containing stream being acidic metal sulfate stream, the dosages may generally be in the range of from 1 to 10 mole dialkyldithiophosphate per mole of heavy metal, based on the type of heavy metal ions to be removed. Most typically, the dosages can be from 2 to 4 mole dialkyldithiophosphate per mole of heavy metal ions to be removed. In the case of several heavy metal ions present, the total dose should be the sum of the individual heavy metal dosages. In any or all embodiments, the weight ratio of the at least one dialkyldithiophosphate compound with the alkyl chain length of C2 to C12 to the at least one phosphonate compound is from 1000:1 to 5:1. In a preferred embodiment, the weight ratio of the at least one dialkyldithiophosphate compound with the alkyl chain length of C2 to C12 to the phosphonate compound is from 100:1 to 10:1, preferably from 70:1 to 30:1. In any or all embodiments, the weight ratio of the at least one dialkyldithiophosphate compound with the alkyl chain length of C2 to C12 to the at least one surfactant is from 1000:1 to 5:1. In a preferred embodiment, the weight ratio of the at least one dialkyldithiophosphate compound with the alkyl chain length of C2 to C12 to the at least one surfactant is from 100:1 to 10:1, preferably from 70:1 to 30:1. In any or all embodiments, the weight ratio of the at least one dialkyldithiophosphate compound with the alkyl chain length of C2 to C12 to the at least one dialkyldithiophosphinate compound is from 100:0 to 1:100. In a preferred embodiment, the weight ratio of the at least one dialkyldithiophosphate compound with the alkyl chain length of C2 to C12 to the at least one dialkyldithiophosphinate compound is from 1:20 to 20:1, preferably from 1:10 to 10:1. According to one or more embodiments, the acid-containing stream being phosphoric acid stream, the solution containing phosphoric acid has a P₂O₅ concentration from 4 wt. % to 70 wt. %, typically from 25 wt. % to 60 wt. %. Specific concentrations of P2O5 contemplated for use with the invention include 25 wt. %, 28 wt. %, 30 wt. %, 42 wt. %, 44 wt. %, 52 wt. %, 54wt. %, 57 wt. %, and 60 wt. %. According to one or more embodiments, the acid-containing stream being acidic metal sulfate stream, the solution containing acidic metal sulfates, has a pH from 0 to 6, typically from 1 to 6. The compositions and processes described herewith as the present invention can be used over a wide temperature range. In any or all embodiments, for example, the processes according to the invention can be performed at a temperature from 0 °C to 120 °C, in particular from 0 °C to 80 °C. Preferably, the temperature is in the range from 20 °C to 80 °C, more preferably from 20 °C to 70 °C, in particular from 20 °C to 60°C. In any or all the embodiments according to the present invention, the process can further comprise adding an effective amount of a reducing agent and/or an adsorbent to the solution containing acid. Such agents are known to be useful in the field. In certain circumstances one or both of these agents can enhance the activity of the reagent including the at least one dialkyldithiophosphate compound with the alkyl chain length of C2 to C12 and the at least one phosphonate compound, and optionally the at least one surfactant and/or the at least one dialkyldithiophosphinate compound. In the same or alternate embodiments, the reducing and/or adsorbent agent can be added to the acid-containing streams all in one stage or added in several stages. In the same or other embodiments, the reducing and/or adsorbent agent can be added together as a blend with the reagent including the at least one dialkyldithiophosphate compound with the alkyl chain length of C2 to C12 and the at least one phosphonate compound, and optionally the at least one surfactant and/or the at least one dialkyldithiophosphinate compound, or separately in any order with the at least one dialkyldithiophosphate compound with the alkyl chain length of C2 to C12 and the at least one phosphonate compound, and optionally the at least one surfactant and/or the at least one dialkyldithiophosphinate compound such as concurrently together or sequentially. While the nature and quantity of the reducing and/or adsorbent agents used depends on the particular composition of the acid-containing solution, and of the purity specifications, those skilled in the art will be able to determine the optimum dosage range using no more than routine experimentation. Reducing agents useful in any or all processes according to the invention include, but are not limited to, iron powder, zinc, red phosphorus, iron (II) sulfate, sodium hypophosphite, hydrazine, hydroxymethane sulfonate, and mixtures thereof. In any of the foregoing or additional embodiments of the process, the process can further comprise adding an effective amount of a reducing agent to the acid-containing stream. In the same or other embodiments, the reducing agent is selected from the group consisting of sodium hypophosphite, hydrazine, iron (II) sulfate, iron powder, and mixtures of any of the foregoing. In a preferred embodiment, the reducing agent is iron powder and sodium hypophosphite. In any or all embodiments of the process, the reducing agent can be added prior to, or together with, the reagent. According to one or more embodiments, the acid-containing stream being phosphoric acid stream, the reducing agent is used in an amount from 0.01 kg to 50 kg of reagent per ton of P2O5, based on the type and quantity of the oxidants in the phosphoric acid solution, which can be readily determined by those skilled in the art using no more than routine methods. In preferred embodiments, the amount of reducing agent is from 0.1 kg to 5 kg of reagent per ton of P2O5 of the phosphoric acid solution. Adsorbent agents can be useful in any or all embodiments according to the invention and include, but are not limited to, active charcoal/carbon, carbon black, ground lignite, adsorbents containing silicate (e.g., synthetic silicic acids, zeolites, calcium silicate, bentonite, perlite, diatomaceous earth, and fluorosilicate), calcium sulfate (including gypsum, hemihydrate, and anhydride), oxides or hydroxides of iron, aluminum, copper or manganese, and mixtures thereof. In any of the foregoing or additional embodiments of the process, the process can further comprise adding an effective amount of an adsorbent to the acid-containing stream. In the same or other embodiments, the adsorbent is selected from the group consisting of calcium sulfate, fluorosilicate, activated carbon, oxides or hydroxides of iron, aluminum, copper, or manganese and mixtures of any of the foregoing. In any or all embodiments, the adsorbent is present in an amount from 0.05 wt. % to 50 wt. %, and preferably from 0.1 wt. % to 30 wt. %, based on the quantity of acid in the solution. In the same or other embodiment, the process is performed at a temperature from 0 ˚C to 120 ˚C; preferably from 20 ˚C to 80 ˚C. In any of the foregoing or additional embodiments of the process, the process can comprise the step of filtering the acid-containing streams prior to adding the reagent. In any of the foregoing or additional embodiments of the process, the at least one dialkyldithiophosphate compound with the alkyl chain length of C2 to C12 and the at least one phosphonate compound, and optionally the at least one surfactant and/or the at least one dialkyldithiophosphinate compound, of the reagent are added simultaneously, in the form of blend, to the acid-containing stream. In any of the foregoing or additional embodiments, the heavy metal ions that are complexed by the reagent and removed by separation are selected from the group consisting of titanium, chromium, cadmium, arsenic, mercury, copper, lead, and mixtures of any of the foregoing. In the same or other embodiment, said heavy metal ions are selected from the group consisting of cadmium, copper, arsenic, mercury, lead, and mixtures thereof. In a preferred embodiment, the heavy metal ions comprise cadmium and/or arsenic and/or copper. In a specific preferred embodiment, the heavy metal ion is cadmium. In another specific preferred embodiment, the heavy metal ion is arsenic. While various embodiments may have been described herein in singular fashion, those skilled in the art will recognize that any of the embodiments described herein can be combined in the collective. Indeed, the invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will satisfy applicable legal requirements. Examples The following examples are provided to assist one skilled in the art to further understand certain embodiments of the present invention. These examples are intended for illustration purposes and are not to be construed as limiting the scope of the various embodiments of the present invention, as defined by the claims. The performances of blends of at least one dialkyldithiophosphate compound with the alkyl chain length of C2 to C12 and the at least one phosphonate compound, and optionally of the at least one surfactant and/or the at least one dialkyldithiophosphinate compound, to remove heavy metals are evaluated with phosphoric acid and phosphoric acid slurries and with acidic metal sulfate solutions. The phosphoric acids with different P₂O₅ levels are obtained from industrial phosphoric acid processing plants. The phosphoric acid slurries are generated by mixing plant gypsum solids with plant phosphoric acid. To separate the heavy metal precipitates from the acid, either a syringe filter or a vacuum filtration is used. Afterwards, the filtrate acids are analyzed with ICP (Inductively Coupled Plasma) to determine the level of various heavy metal elements. The general procedure for the test and experimental examples is outlined below. Phosphonate compound (diethylenetriamine penta(methylene phosphonic acid), or DTPMP) was purchased from ZSCHIMMER & SCHWARZ Inc. with the product name CUBLEN DNC 450. The sodium diisobutyl dithiophosphinate (“Na-DTPi”), Dioctyldithiophosphinic acid (CYANEX 301), and the sodium dioctylsulfosuccinate (AEROSOL OT70PG – “Surfactant C”) were obtained from Syensqo SA. The alkyldiphenyloxide disulfonate surface active solution (DOWFAX® 8390 – “Surfactant A”) was purchased from Dow Chemicals. The polyethyleneglycol sorbitol hexaoleate (ATLAS® G1086 – “Surfactant B”) was purchased from Croda. The dialkyldithiophosphate compounds with various chain lengths were synthesized in Syensqo laboratories. The blend was prepared by combining the phosphonate compound, and dialkyldithiophosphate compounds with various chain lengths. Some blends further comprise the surfactant and/or the Na-DTPi (Sodium diisobutyl dithiophosphinate) or Dioctyldithiophosphinic acid (CYANEX 301). The dialkyldithiophosphate compounds with various chain lengths were synthesized as explained in Example 1 below. Example 1 - Preparation of the dialkyldithiophosphate compounds Example 1-A: Synthesis of ammonium di(2-ethylhexyl) dithiophosphate (“C8DTP- NH₄ Salt”) To a 250 ml 3-neck round bottom flask equipped with a heating mantle, magnetic stirring, nitrogen flow and vent to a caustic scrubber was added 155.57 g (1.1946 moles) of 2-ethylhexanol (2mole% excess). After heating to 40 °C, 65.00 g of P2S5 (0.1464 moles) was added in three equal portions over 30 minutes with vigorous stirring. The reaction temperature was then increased to 80 °C where it was held for 4 hours. The reaction product was cooled and filtered to yield a light yellow, low viscosity liquid. (³¹P NMR δ 85ppm, 85.4%). To a 250ml 3-neck round bottom flask equipped with a heating mantle, magnetic stirring, and nitrogen flow was added 100.00g g (0.2823 moles) of the prepared di(2- ethylhexyl) dithiophosphoric acid. With vigorous agitation, 18.55 g of 28% aqueous ammonium hydroxide (2 mole% excess) was added to the reactor. An ice bath was raised and the addition rate was controlled to maintain the reaction temperature below 40°C. The reaction product was a light yellow, low viscosity liquid. (³¹P NMR δ 111ppm, 93.1%). Example 1-B: Synthesis of di(3,7-dimethyloctyl) dithiophosphoric acid (“C10DTP”) To a 250ml 3-neck round bottom flask equipped with a heating mantle, magnetic stirring, nitrogen flow and vent to a caustic scrubber was added 159.99 g (1.0108 moles) of 3,7-dimethyloctanol (2mole% excess). After heating to 40 °C, 80.00 g of P2S5 (0.1239 moles) was added in three equal portions over 30 minutes with vigorous stirring. The reaction temperature was then increased to 80 °C where it was held for 4 hours. The reaction product was cooled and filtered to yield a light yellow, low viscosity liquid. (³¹P NMR δ 85ppm, 86.1%). Example 2 - Process for removing heavy metals from concentrated phosphoric acids from production plants (~ 57% P2O5) at elevated temperature (65˚C) 50 g of concentrated phosphoric acid from the plant (~ 57 % P2O5, collected from the clarification tank after filtration) was transferred into a glass jar with a magnetic stir bar. The acid was heated to 65 °C in a water bath. An effective amount of a reagent of interest (as listed in Table 1) was dosed into acid under agitation at 350 rpm. After agitation for 1 minute the acid was sampled using a syringe and filtered with a 0.2 µm polyvinylidene difluoride (PVDF) syringe filter. After 5 minutes of agitation another sample was drawn using a syringe from the same glass jar and filtered with 0.2 µm polyvinylidene difluoride (PVDF) syringe filter. The filtrates of 1 minute and 5 minutes samples were collected and then submitted for ICP elemental analysis. The ICP results of the leftover Cd in filtered phosphoric acid and the corresponding calculated percentage of Cd removed are shown in Table 1. The lower the leftover Cd and the higher the percentage of Cd removed, the better the performance of reagents. As shown in Samples 1A-2 and 1A-7 of Table 1, phosphonate reagent by itself showed minimum/no performance in removing Cd from plant concentrated phosphoric acid (57% P₂O₅). However, it is unexpected to observe that when phosphonate compound was combined with C8DTP NH₄ salt reagent variants (Samples 1A-4, 1A-6, 1A-9), significantly more cadmium from the concentrated phosphoric acid was removed compared to the samples without phosphonate compound (Samples 1A-3, 1A-5, 1A-8,).

Table 1. Percentage Plant Dosage, Temp. Treatment Cd, of Cd Sample Phosphoric (_˚C) ^Reagents (kg/T Time, min ppm removed, Acid Source P2O5) % Concentrated 1A-1 Acid 57% 65 Control 0 - 31.9 - P₂O₅ Concentrated 1A-2 Acid 57% 65 Phosphonate 2 1 31.5 1.3 P₂O₅ Concentrated 1A-3 Acid 57% 65 C8DTP NH₄ Salt in Water 2 1 30.2 5.3 P₂O₅ Concentrated 1A-4 Acid 57% ^{65 C8DTP NH4 Salt +} 5_Phosph ^{2 1 27.1 15.0} P₂O _{onate(1wt.%) in Water} Concentrated 1A-5 Acid 57% ₆₅ ^{C8DTP NH} ₄ ^{Salt +Surfactant} 2 1 20.3 36.4 A (1wt.%) in Water P₂O₅ Concentrated C8DTP NH₄ Salt +Surfactant 1A-6 Acid 57% 65 A (1 wt.%) +Phosphonate (1 2 1 12.8 59.9 P₂O₅ wt.%) in Water Concentrated 1A-7 Acid 57% 65 Phosphonate 2 5 31.6 0.9 P₂O₅ Concentrated 1A-8 Acid 57% ₆₅ ^{C8DTP NH4 Salt +Surfactant} A_{(1wt.%) i 2 5 4.6 85.6} P₂O_{5 n Water} Concentrated C8DTP NH₄ Salt + Surfactant 1A-9 Acid 57% 65 A (1 wt.%) +Phosphonate (1 2 5 1.4 95.6 P₂O₅ wt.%) in Water Example 3 - Process for removing heavy metals from phosphoric acids slurry containing gypsum solids (~ 30 % P2O5) at elevated temperature (72˚C) 50 g of phosphoric acid slurry containing ~30 wt. % gypsum solids (~ 30 % P₂O₅, collected from the stream feeding the gypsum filters) was transferred into a glass jar with a magnetic stir bar. The slurry was heated to 72 °C in a water bath. An effective amount of a reagent of interest (as listed in Table 2) was dosed into the slurry under agitation at 350 rpm. After agitation for 10 minutes, the acid was sampled using a syringe and filtered with a 0.2 µm polyvinylidene difluoride (PVDF) syringe filter. After 30 minutes of agitation, another sample from the same glass jar was drawn using a syringe and filtered with a 0.2 µm polyvinylidene difluoride (PVDF) syringe filter. The filtrates of 10 minutes and 30 minutes samples are collected and then submitted for ICP elemental analysis. The ICP results of the leftover Cd in filtered phosphoric acid and the corresponding calculated percentage of Cd removed are shown in Table 2. The lower the leftover Cd and the higher the percentage of Cd removed, the better the performance of reagents. From Table 2 it can be seen that even though phosphonate reagent by itself (Sample 2A-2, 2A-7) showed minimum/no performance in removing Cd from plant weak phosphoric acid slurry (30% P₂O₅), all the C8DTP NH₄ Salt reagent variants (2A-4, 2A-6, 2A-9, 2A-11) when combined with phosphonate compound were able to reduce significantly more cadmium from the concentrated phosphoric acid compared to the reagent variants (2A-3, 2A-5, 2A-8, 2A-10) of C8DTP NH₄ Salt without the phosphonate. Table 2.

Plant Dosage, Percentage Temp. Treatment Cd, Sample Phosphoric (_˚C) ^Reagents (kg/T of Cd 2₅ Time, min ppm Acid Source P O ) removed, % Weak Acid 2A-1 Slurry 30% 72 Control 0 - 16.2 - P₂O₅ Weak Acid 2A-2 Slurry 30% 72 Phosphonate 1.5 10 16.0 1.2 P₂O₅ Weak Acid 2A-3 Slurry 30% ₇₂ ^{C8DTP NH4 Salt in} _{1.5 10 1} ₂O_{5 Wa 0.6 34.6} P _ter Weak Acid C8DTP NH₄ Salt + 2A-4 Slurry 30% 72 Phosphonate (1 1.5 10 9.1 43.8 P₂O₅ wt.%) in Water Weak Acid C8DTP NH₄ Salt + 2A-5 Slurry 30% 72 Surfactant A 1.5 10 6.9 57.4 P₂O₅ (1wt.%) in Water C8DTP NH₄ Salt + Weak Acid Surfactant A (1 2A-6 Slurry 30% 72 1.5 10 5.0 69.1 wt.%) +Phosphonate P₂O₅ (1 wt.%) in Water Weak Acid 2A-7 Slurry 30% 72 Phosphonate 1.5 30 16.0. 1.2 P₂O₅ Weak Acid 2A-8 Slurry 30% ₇₂ ^{C8DTP NH4 Salt in} _{1.5 30 6.8 58.0} P₂O_{5 Water} Weak Acid C8DTP NH₄ Salt + 2A-9 Slurry 30% 72 Phosphonate (1 1.5 30 5.5 66.0 P₂O₅ wt.%) in Water Weak Acid C8DTP NH₄ Salt + 2A-10 Slurry 30% 72 Surfactant A 1.5 30 4.4 72.8 P₂O₅ (1wt.%) in Water C8DTP NH₄ Salt Weak Acid +Surfactant A (1 2A-11 Slurry 30% 72 wt.%) + 1.5 30 1.5 90.7 P₂O₅ Phosphonate(1 wt.%) in Water Example 4 - Process for removing heavy metals from concentrated phosphoric acids from production plants (~ 63 % P2O5) at elevated temperature (65˚C) 50 g of concentrated phosphoric acid from the plant (~ 63 % P2O5, collected from the clarification tank after filtration) was transferred into a glass jar with a magnetic stir bar. The acid was heated to 65 °C in a water bath. An effective amount of a reagent of interest (as listed in Table 3) was dosed into acid under agitation at 350 rpm. After agitation for 1 minute the acid was sampled using a syringe and filtered with a 0.2 µm polyvinylidene difluoride (PVDF) syringe filter. After 5 minutes of agitation another sample was drawn using a syringe from the same glass jar and filtered with 0.2 µm polyvinylidene difluoride (PVDF) syringe filter. The filtrates of 1 minute and 5 minutes samples were collected and then submitted for ICP elemental analysis. The ICP results of the leftover As and Cd in filtered phosphoric acid and the corresponding calculated percentage of As and Cd removed are shown in Table 3. The lower the leftover As and Cd and the higher the percentage of As and Cd removed, the better the performance of reagents. From Table 3, it can be seen that all the C8DTP NH4 Salt reagent variants with phosphonate were able to reduce significantly more cadmium from the concentrated phosphoric acid compared to the reagent variants of C8DTP NH₄ Salt without the phosphonate.

Table 3. Plant Temp. Dosage Treatme % of As % of Cd Sample Phosphoric _(˚C) ^Reagents (kg/T nt removed Cd, removed 2_{5 Tim} ^{As, ppm} Acid Source P O ) _{e min} % ppm % 3A-1 ^Concentrated A_{cid 63% P2O5} 65 Control 0 - 9.1 - 28.5 - C8DTP NH₄ C^oncentrat Salt +Na-DTPi 3^{A-2 ed} A_{cid 63% P2O5} ⁶⁵ +Surfactant A 3 1 9.0 1.1 16.5 42.1 (1 wt.%) in Water C8DTP NH₄ Salt +Na-DTPi 3^{A-3 Concentrated} +Surfactant A A_{cid 63% P2O5} ⁶⁵ (1 wt.%) + 3 1 8.1 11.0 11.1 61.1 Phosphonate (1wt. %) in Water C8DTP NH4 3^{A-4 Concentrated} Salt +Na-DTPi A_{cid 63% P2O5} ⁶⁵ +Surfactant A(1 3 5 4.1 54.9 4.9 82.8 wt.%) in Water C8DTP NH₄ Salt +Na-DTPi +S 3^{A-5 Concentrated} urfactant A(1 A_{cid 63% P2O5} ⁶⁵ wt.%) + 3 5 2.5 72.5 2.5 91.2 Phosphonate (1wt. %) in Water Example 5 - Process for removing heavy metals from pH 2 sulfuric acid solutions To one liter of pH 2 sulfuric acid, 0.025 g of sodium (meta)arsenite and 0.035 g of cadmium sulfate was added to achieve around 15 ppm of arsenic and 20 ppm of cadmium in the acid solution.50 g of the prepared acid solution was transferred into a glass jar with a magnetic stir bar. An effective amount of a reagent of interest (as listed in Table 4) was dosed into the acid solution under agitation at 350 rpm. After agitation for 2 minutes a sample was collected using a syringe and filtered with a 0.2 µm polyvinylidene difluoride (PVDF) syringe filter. The filtrate was collected and then submitted for ICP elemental analysis. The ICP results of the leftover Arsenic and Cadmium in the filtered sulfuric acid solution and the corresponding calculated percentage of Arsenic and Cadmium removed are shown in Table 4. The lower the leftover Arsenic and Cadmium and the higher the percentage of Arsenic and Cadmium removed, the better the performance of reagents. From Table 4, it can be seen that all the C8DTP NH4 Salt reagent variants with phosphonate were able to reduce significantly more heavy metal from the sulfuric acid solution compared to the reagent variants of C8DTP NH4 Salt without the phosphonate.

Table 4: Percentage Percentage Acid Dosage, Treatment As, Cd, Sample S_ource ^Reagents of As of Cd ppm Time, min ppm ppm removed, % removed, % Sulfuric 4A-1 A_{cid pH 2} ^{Control 0 2 14.3 20.6} Sulfuric 4A-2 A_{cid pH 2} ^{Phosphonate 230 2 14.5 0 20.9 0} C8DTP NH Salt Sulfuric 4 4A-3 + Surfactant B (1 259 2 10.8 24.5 0.0 100 Acid pH 2 wt%) in Water C8DTP NH4 Salt 4^{A-4 Sulfuric} + Surfactant B (1 A_{cid pH 2} wt%) + 259 2 3.4 76.2 0.0 100 Phosphonate (1 wt %) in Water 4^{A-5 Sulfuric} C8DTP NH₄ Salt A_{cid pH 2} + Surfactant A (1 259 2 12.5 12.6 0.0 100 wt%) in Water C8DTP NH₄ Salt 4^{A-6 Sulfuric} + Surfactant A (1 A_{cid pH 2} wt%) + 259 2 8.0 44.1 0.0 100 Phosphonate (1wt %) in Water C8DTP NH₄ Salt 4^{A-7 Sulfuric} + NaDTPi + A_{cid pH 2} 271 2 9.8 31.5 0.5 97.6 Surfactant A (1 wt%) in Water C8DTP NH₄ Salt + NaDTPi + 4_A-8 ^Sulfuric Surfactant A (1 269 2 6.3 55.9 0.0 100 Acid pH 2 wt%) + Phosphonate (1wt %) in Water 4^{A-9 Sulfuric} C8DTP NH4 Salt A_{cid pH 2} + CYANEX 301 264 2 10.6 25.9 0.0 100 in Water C8DTP NH4 Salt 4_A-10 ^Sulfuric + CYANEX 301 271 2 0.0 99.9 0.0 100 Acid pH 2 + Phosphonate (1 wt%) in Water 4^{A-11 Sulfuric} C10 DTP Acid + A_{cid pH 2} Surfactant C (5 288 2 11.6 18.9 15.8 23.3 wt%) in Water C10DTP Acid + S^ulf Surfactant C (5 4_A-12 ^uric wt%) + 287 2 9.9 30.8 12.0 41.7 Acid pH 2 Phosphonate (1 wt%) in Water Various patent and/or scientific literature references have been referred to throughout this application. The disclosures of these publications in their entireties are hereby incorporated by reference as if written herein. However, if a term in the present application contradicts or conflicts with a term in the incorporated reference, the term from the present application takes precedence over the conflicting term from the incorporated reference. In view of the above description and the examples, one of ordinary skill in the art will be able to practice the disclosure as claimed without undue experimentation. While typical embodiments have been set forth for the purpose of illustrating the fundamental novel features of the present invention, the foregoing descriptions should not be deemed to be a limitation on the scope herein. Accordingly, various modifications, adaptations, and alternatives can occur to one skilled in the art without departing from the spirit and scope of the invention described herein, and the scope of the invention should be defined by the appended claims.

Claims

CLAIMS 1. A composition for forming complexes with heavy metal ions in an acid-containing stream, wherein the composition comprises an effective amount of: at least one dialkyldithiophosphate compound with the alkyl chain length of C2 to C12; and at least one phosphonate compound. 2. The composition according to claim 1, wherein said dialkyldithiophosphate compound with the alkyl chain length of C2 to C12 is selected from the group consisting of dialkyldithiophosphoric acid with the alkyl chain length of C2 to C12 and salts of any of the foregoing dialkyldithiophosphoric acid with the alkyl chain length of C2 to C12 in the form of calcium, magnesium, potassium, sodium salt or ammonium salt with the formula NR1R2R3R4⁺, where R1, R2, R3, R4 are, equal to or different from each other, independently chosen from hydrogen, alkyl or aryl groups; and mixtures thereof. 3. The composition according to claims 1 or 2, wherein said dialkyldithiophosphate compound has an alkyl chain of C6 to C12, preferably C8 to C10. 4. The composition according to any one of claims 1 to 3, wherein said dialkyldithiophosphate compound has a C8 alkyl chain. 5. The composition according to any one of claims 2 to 4, wherein said dialkyldithiophosphate compound is selected from the group consisting of any salts of di(1,3-dimethylbutyl) dithiophosphoric acid, di(2-ethylhexyl) dithiophosphoric acid, di(3,7-dimethyloctyl) dithiophosphoric acid, di(2-butyloctanol) dithiophosphoric acid, and mixtures thereof. 6. The composition according to claim 5, wherein said dialkyldithiophosphate compound is salts of di(2-ethylhexyl) dithiophosphoric acid. 7. The composition according to claim 6, wherein said dialkyldithiophosphate compound is ammonium di(2-ethylhexyl) dithiophosphate. 8. The composition according to any one of claims 1 to 7, wherein the phosphonate compound comprises the formula (I): wherein R” is an optionally substituted hydrocarbyl radical comprising from about 1 to about 20 carbons; R’ is H, optionally substituted C1-C20 alkyl, optionally substituted C6-C12 aryl, optionally substituted C7-C20 aralkyl, optionally substituted C2-C20 alkenyl, Group I metal ion, Group II metal ion, or NR₁R₂R₃R₄ ⁺, where R₁, R₂, R₃, R₄ are, equal to or different from each other, independently chosen from hydrogen, alkyl, alkenyl, or aryl groups. 9. The composition according to any one of claims 1 to 8, wherein the phosphate compound is selected from diethylenetriaminepentakis(methylphosphonic acid), nitrilotri(methylphosphonic acid), iminodi(methylphosphonic acid), (aminomethyl)phosphonic acid, N,N-bis(phosphonomethyl)glycine, glyphosate, and mixtures thereof. 10. The composition according to claim 9, wherein the phosphate compound is diethylenetriaminepentakis(methylphosphonic acid). 11. The composition according to any one of claims 1 to 10, wherein the reagent further comprises at least one surfactant. 12. The composition according to any one of claims 1 to 11, wherein the reagent further comprises at least one dialkyldithiophosphinate compound. 13. The composition according to claims 11 or 12, wherein said surfactant is selected from the group consisting of sulfosuccinates, aryl sulfonates, alkaryl sulfonates, diphenyl sulfonates, olefin sulfonates, sulfonates of ethoxylated alcohols, petroleum sulfonates, sulfosuccinamates, alkoxylated surfactants, ester/amide surfactants, EO/PO block copolymers, and mixtures thereof. 14. The composition according to any one of claims 12 or 13, wherein said dialkyldithiophosphinate compound is selected from the group consisting of dialkydithiophosphinic acid and salts of any of the foregoing dialkyldithiophosphinic acid in the form of calcium, magnesium, potassium, sodium salt or ammonium salt with the formula NR₁R₂R₃R₄ ⁺, where R₁, R₂, R₃, R₄ are, equal to or different from each other, independently chosen from hydrogen, alkyl or aryl groups; and mixtures thereof. 15. The composition according to claim 14, wherein said dialkyldithiophosphinate compound is selected from the group consisting of salts of diisobutyl dithiophosphinic acid; bis(2,4,4-trimethylpentyl) dithiophosphinic acid; and mixtures thereof. 16. The composition according to claim 15, wherein said dialkyldithiophosphinate compound is sodium diisobutyl dithiophosphinate. 17. The composition according to any one of claims 1 to 16, wherein the weight ratio of the at least one dialkyldithiophosphate compound with the alkyl chain length of C2 to C12 to the at least one phosphonate compound is from 1000:1 to 5:1, preferably from 100:1 to 10:1, and preferably from 70:1 to 30:1. 18. The composition according to any one of claims 1 to 17, wherein the weight ratio of the at least one dialkyldithiophosphate compound with the alkyl chain length of C2 to C12 to the at least one surfactant is from 1000:1 to 5:1, preferably from 100:1 to 10:1, more preferably from 70:1 to 30:1. 19. The composition according to any one of claims 1 to 18, wherein the weight ratio of the at least one dialkyldithiophosphate compound with the alkyl chain length of C2 to C12 to the at least one dialkyldithiophosphinate compound is from 100:0 to 1:100, preferably from 1:20 to 20:1, more preferably from 1:10 to 10:1. 20. A process for removing heavy metal ions from an acid-containing stream, said process comprising: adding an effective amount of a reagent comprising a composition as defined in any one of claims 1 to 19 to the acid-containing stream to form heavy metal ion complexes, and separating the heavy metal ion complexes from the acid-containing stream. 21. The process according to claim 20, wherein the dialkyldithiophosphate compound is in a diluted solution when it is added to the acid-containing stream. 22. The process according to claim 20 or 21, wherein the process is performed at a temperature from 0 ˚C to 120 ˚C. 23. The process according to any one of claims 20 to 22, wherein the process further comprises adding an effective amount of a reducing agent to the acid-containing stream, wherein said reducing agent is selected from the group consisting of sodium hypophosphite, hydrazine, iron (II) sulfate, iron powder, and mixtures thereof. 24. The process according to any one of claims 20 to 23, wherein the process further comprises adding an effective amount of an adsorbent to the acid-containing stream, wherein said adsorbent is selected from the group consisting of calcium sulfate, fluorosilicate, activated carbon, oxides or hydroxides of iron, aluminum, copper, or manganese, and mixtures thereof. 25. The process according to any one of claims 20 to 24, wherein the process further comprises filtering the acid-containing stream prior to adding the reagent. 26. The process according to the claims 20 to 25, wherein the acid-containing stream is a phosphoric acid containing stream. 27. The process according to claim 26, wherein the phosphoric acid containing stream has a concentration from 4 % to 70 % P2O5, preferably from 25 % to 60 % P2O5. 28. The process according to the claims 20 to 25, wherein the acid-containing stream is an acidic metal sulfate stream. 29. The process according to the claim 28, wherein the solution containing acidic metal sulfate has a pH from 0 to 6, preferably from 1 to 6. 30. The process according to any one of claims 20 to 29, wherein said heavy metal ions removed from the acid-containing stream are selected from the group consisting of titanium, chromium, cadmium, arsenic, mercury, copper, lead, and mixtures thereof. 31. The process according to claim 30, wherein the heavy metal ions removed are cadmium. 32. The process according to claim 30, wherein the heavy metal ions removed are arsenic.