RU2395600C2 - Procedure for extracting arsenic from water solutions - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention refers to hydro-metallurgy of non-ferrous metals, particularly to procedures of extracting arsenic from solutions and can be implemented for extracting arsenic from sewage of metallurgical, chemical and other branches of industry and also at production of metals from secondary raw materials. The procedure for extracting arsenic from solutions containing a row of metals consists in sedimentation of arsenic in form of arsenate by adding compounds of iron. For sedimentation there are used compounds of iron modified with cation surface active substance (SAS) of nano-crystals of akaganeite β-Fe³⁺O(OH) in the nano-structure range within limits from 2.12 to 2.34 nm and at pH 6-8. Arsenates are settled from solutions of arcenic ions concentration equal to 0.5-1.0 mg/l. Crystals of akaganeite modified with cation surface active substance are produced by means of sorption of cation surface active substance - hexyldecyl trimethyl ammonia bromide (HDTMBr) on akaganeite, osmosis on a membrane M 45 and sublimation drying at room temperature.

EFFECT: reduced expenditures and raised efficiency of arsenic extraction.

3 cl, 3 dwg, 1 tbl

Description

The invention relates to hydrometallurgy of non-ferrous metals, in particular to methods for extracting arsenic from solutions, and can be used to extract arsenic from wastewater of metallurgical, chemical and other industries, as well as in the production of metals from secondary raw materials. To extract As from dilute solutions, iron hydroxides were used, which were used as β-FeO (OH) acaganeite nanocrystals modified with a cationic surfactant.

Known methods for removing arsenic from dusts of lead-zinc production into non-toxic arsenic sulfide by sulfidization of the material with elemental sulfur, leaching with sodium sulfide, and from the solution arsenic is precipitated as sulfides with sulfuric acid at pH 2 by known methods [1-2]. A known method of removing arsenic, in which precipitate of Fe (OH) _{3 is} used to separate As from a solution, is formed as a result of oxidation by oxygen under pressure of Fe ^{2+ ions} contained in the solution or added as FeSO ₄ . The degree of coprecipitation of As compounds at pH 3.5–4.6 reaches 99.5% and depends on the ratio of Fe ³⁺ / As [3].

To extract arsenic anions, the most common is their deposition by coagulation with aluminum and iron salts. Arsenic (V) oxyanions were removed from dilute aqueous solutions by sorption on fine particles of synthetic goethite FeO (OH) and iron hydroxides [4].

The closest in technical essence and the achieved result to the proposed is a method for processing arsenic dusts and sublimates, including their leaching and separation from solutions of arsenates, an addition of ferric salt is introduced into the starting material, and leaching is carried out with a solution containing 280-300 g / l sodium chloride and 0.5-1.0 g / l hydrochloric acid at 85-100 ° C, pH 0.8-1.2 and sparging with air, and the deposition of iron arsenates is carried out at pH 2.2-2.8 [4].

The technical result of the invention is an increase in the degree of extraction of arsenic from solutions, it is proposed to use a precipitate of acaganeite modified with a surfactant, withdrawal of arsenic to a low toxic form of iron arsenate, which does not require the construction of a special expensive disposal facility. The advantage of the proposed method is that it is suitable for low concentrations of extracted ions of 5-10 mg / l, when particles cannot be effectively isolated by existing methods.

The invention is illustrated by drawings, where figure 1 presents the results of a comparison of experimental absorption data with theoretical curves for the equation of kinetics of the first order; figure 2 shows the effect of pH on the removal (R%) of As (the concentration of the modified acaganeite sorbent is 0.5 g / l, the initial concentration of As (III) is 10 mg / l, the contact time is 24 hours and the temperature is 298 K) and figure 3 shows the sorption isotherms of arsenates on Ak and Ak _m under various experimental conditions: a sample of modified acaganeite 0.5 g / l, temperature 25 ° C, contact time 24 hours

A method is proposed for extracting arsenic from solutions containing a number of metals, including the precipitation of arsenic in the form of arsenates by adding an iron compound by using β-Fe ³⁺ O (OH) nanocrystals of acaganeite nanocrystals modified as cationic iron compounds in the range of 2 , 12 to 2.34 nm at an ionic strength of 0.1 KNO ₃ and at pH 4.5. Modified Akaganeit Ak _{m was} prepared after sorption of a cationic surfactant - hexyldecyl trimethyl ammonium bromide (GDTMBr) on acaganite.

Used acaganeite (AK) nanocrystals with a surface area of 299-300 m ² / g and a maximum sorption capacity of 100-120 mg As (V) per g of acaganeite are obtained by precipitation of iron (III) chloride with ammonium carbonate, osmosis on an M 45 membrane and freeze-drying at room temperature.

Ak _{m is} effective in removing arsenic arsenates from aqueous solutions. The maximum sorption of arsenic arsenates was established 328.3 mg / g in a wide pH range, which is significantly higher than for all known sorbents.

The synthesis of modified Akaganite Ak _{m was} carried out as follows. 100 ml of a 0.01 M cationic surfactant solution was added to 200 ml flasks. Each solution contained 1.0 g of Ak, and the pH was adjusted to 11.

The solution was stirred in a bath at a temperature of 25-1 ° C for 24 hours with a shaker until the sorption equilibrium (GDTMBr) was reached. The suspension liquid was separated on a 0.45 μm membrane and then the sorbent was sent to freeze-drying. The adsorption data of GDTMBr on acaganeite corresponds to the Freundlich equation of the type: Q _eq = K _F · C _eq ^{1 / n} , where Q _eq is the amount of GDTMBr sorbed per unit weight of the solid sorbent (Ak), C _eq is the concentration of solute in solution at equilibrium, and K _F and 1 / n are constants showing adsorption capacity and adsorption intensity, respectively.

The value of these constants is presented in the table.

Table The equilibrium parameters for Akaganite Ak and Akaganite Ak _m for various experimental conditions Material pH (-) Langmuir constants Freundlich constants R ² (-) Qmax (mg / g) K _L (L mg / L) R ² (-) K _F (mg / g) 1 / n (-) GDTMVr on Ak 0,994 765.0 0.003 0,998 0.7 7,376 As (III) on Ak four 0.939 75.9 0.217 0.965 21.6 2,837 As (III) on Ak 7 0,994 135.2 0,063 0.989 12.7 1,686 As (III) on Akm 7 0,990 328.3 0,042 0.986 18.9 1,424 As (III) on Akm four 0.866 169.6 0.104 0.766 33.8 2,510

Sorption of HDTMBr is described by the Langmuir isotherm with a correlation coefficient (R ² ) above 0.99, and the maximum adsorption (Qmax) was 765 mg / g.

The values of Qmax and K _{L are} also presented in the table. To obtain solutions of arsenic (III), arsenic trioxide of 99.8% purity was used. Solutions with an ionic strength of 0.1 M were used. A portion of modified Akaganite Ak _m weighing 0.5 g / l was placed in a series of flasks with arsenic solutions, varying the initial concentration of As (III) from 0 to 300 mg / l. PH adjustment was carried out with 0.1 M Hcl or 0.1 M NaOH. The residual concentration was determined after membrane filtration on a 0.45 μm membrane. The solutions were stirred with a shaker for 24 hours at 25 ° C until equilibrium was reached. Preliminary experiments found that after 24 hours there was no change in the amount of sorption of arsenic. Figure 1 presents the results.

It was found that the maximum sorption capacity was 328.3 mg of As (III) per g of acaganeite, which is higher compared to other sorbents.

Arsenite precipitation is carried out with the ratio of Fe / As acaganeite iron to arsenic ions equal to 0.5-1.0.

We studied the effect of pH on the removal (R%) of As (the concentration of modified acaganeite sorbent is 0.5 g / L, the initial concentration of As (III) is 10 mg / L, the contact time is 24 hours, and the temperature is 298 K).

Figure 2 presents the results.

As follows from figure 2, the maximum sorption is observed in the range of pH from 6 to 8, the best results are obtained at pH 7.

The removal of As (III) on modified acaganeite was always higher than on unmodified acaganeite (see Fig. 3).

The proposed solution meets the criteria of industrial applicability, novelty and inventive step.

The technical result is to reduce costs and increase the efficiency of wastewater treatment from cations of heavy metals and arsenates.

The source of information

1. Auto 789619 USSR. The method of removing arsenic from dusts of lead-zinc production. Publ. 10/23/80, bull. Number 39.

2. Auto 990841 USSR, C22B 7/02. A method of removing arsenic from lead and zinc dusts, publ. 01/23/1983, bull. Number 3.

3. Japanese application. Taka Shiro, Kudo Tomoshi, Kibayashi Yasushi, Cl. 10A 22, (C22B 3/00 No. 54-82307). The method of removing arsenic from sulfate solutions. Publ. 06/30/79.

4. Auto 914647, USSR, M Cl ³ C22B 7/02. A method of processing arsenic-containing converter dusts and sublimates. Publ. 03/23/1982. Bull. No. 11 (prototype).

Claims (3)

1. The method of extraction of arsenic from solutions containing a number of metals, including the deposition of arsenic in the form of arsenate by adding an iron compound, characterized in that the deposition is carried out using iron compounds modified with cationic surface-active substance (surfactant) acaganeite (β-Fe ^{+ 3} O (OH) in the nanostructured range from 2.12 to 2.34 nm and at a pH of 6-8. 2. The method according to claim 1, characterized in that the deposition of arsenates is carried out from solutions with an arsenic ion concentration of 0.5-1.0 mg / L. 3. The method according to claim 1, characterized in that acaganeite crystals modified with a cationic surfactant with a surface area of 299-300 m ² / g and a maximum sorption capacity of arsenic ions of 328.3 mg As (III) / per gram of acaganeite are obtained by sorption of a cationic surfactant - hexyldecyl trimethyl ammonium bromide (HDTMBr) on acaganeite, osmosis on the M 45 membrane and freeze-drying at room temperature.

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