WO2023148365A1

WO2023148365A1 - A composition for reducing the amount of sodium hydroaluminosilicate desposits and a method for obtaining the composition

Info

Publication number: WO2023148365A1
Application number: PCT/EP2023/052774
Authority: WO
Inventors: Denys BOLHAR; Viktor GORDIIENKO; Yevgen OSTREYKO
Original assignee: Its Water Group Sa
Current assignee: Its Water Group Sa
Priority date: 2022-02-07
Filing date: 2023-02-06
Publication date: 2023-08-10
Anticipated expiration: 2024-08-07
Also published as: EP4476180A1; AU2023214799A1; BR112023019597A2

Abstract

The present invention relates to the mining industry, namely to the methods of obtaining materials and reagents that are used in the technological process of alumina production based on the Bayer method. The invention provides a composition and a method for obtaining more efficient composition, which would provide not only protection of heat exchanger surfaces of evaporators from precipitators from the spent liquor with high content of CO₃ ^2- and SO₄ ^2-, and solids (aluminium hydrate, red mud, etc.), but could also be used in the current technological flow of the Bayer process for washing heating surfaces on the go.

Description

A COMPOSITION FOR REDUCING THE AMOUNT OF SODIUM HYDROALUMINOSILICATE DESPOSITS AND A METHOD FOR OBTAINING

THE COMPOSITION

FIELD OF THE INVENTION

The present invention relates to the mining industry, namely to the methods of obtaining materials and reagents that are used in the technological process of alumina production based on the Bayer method.

BACKGROUND OF THE INVENTION

The world alumina production is based predominantly on the processing of high-quality bauxite. The process of obtaining AI2O3 with a relatively low content of SiCh includes the following stages: autoclave leaching using a caustic soda solution; separating the aluminate solution from the red mud; decomposition of aluminate solution to obtain a caustic solution known as “spent liquor” (C(Na2O) ~ 150 g/dm³) and aluminium hydroxide; calcination of A1(OH)₃.

As the weakly concentrated spent liquor is reheated on the heating surfaces, scale is formed, which is represented mainly in the form «Na2O-A12O3’(l,4-2)SiO2-xH2O and is defined as sodium hydroaluminosilicate (or SHAS). Over time, the scale formation leads to disruptions in the operation of evaporating equipment, namely: increased fuel and energy consumptions and costs; increased alkali consumption to support the caustic module of the circulating solution; reduced throughput of the devices. As a result, the overall throughput of evaporators is reduced, leading to a decrease in alumina production and increased costs.

The chemical composition of SHAS is not constant and changes under the influence of several factors: temperature, composition and concentration of spent liquor. In its composition, the sodium hydroaluminosilicate is comparable with a natural mineral called sodalite - 7(Na2O-A12O3’SiO2)-2NaAlO2-wH2O. The composition of SHAS released the from industrial solutions is much more diverse because in addition to the sodium aluminate, caustic soda and sodium silicate, it may also include sulphates, carbonate or sodium chloride, as well as other compounds depending on the raw materials. The formation of scale with anionic composition which includes ions Cl’, CCh²’ and SCU²’ indicates that the scale also has the presence of sodalite 3(Na2O-A12O3-2SiO2)-2NaCl, cancrinite 3(Na2O-A12O3-2SiO2)-Na2CO3 and nosean 3(Na2O-A12O3-2SiO2)-Na2SO4.

Currently, there are several common ways to restore and sustainably operate evaporating equipment. One of the most common methods is chemical and mechanical cleaning of heat exchange surfaces from scale [Schmidt, R. L., and Featherstone, R. H., 1969, Cleaning Evaporator Tubes, US Patent 3,443,992], However, besides the labour intensity and safety questions associated with this method, it does not prevent the problem but only deals with its consequences. In addition to the method mentioned, there is also an option to apply protective polymer coating on the surface of the heat exchange tubes. However, this method is not practical because any coating thick enough to maintain mechanical integrity would itself significantly reduce the heat transfer [Kazakov V., Potapov N. & Bobrov A. (1979) “Heating and evaporation of silica-containing aluminate liquors”, Tsvetnye Met., no.10, pp. 45-48.; Kazakov V. & Potapov N. (1982) “Use of an organosilicone inhibitor in the evaporation step of aluminate liquors”, Tsvetnye Met., no. 8, pp. 39-41],

A method that became widespread recently is one where a special chemical reagent is added, which is absorbed on the heating surface of the equipment and thus prevents it from scaling.

One of the most popular is reagent MAX HT™ produced by Cytec Industries Inc. [MAX HT™ Sodalite Scale Inhibitor: Plant Experience and Impact on the Process, by Donald Spitzer et. al., Pages 57-62, Light Metals 2008, (2008)], which is a substance consisting of silane functional groups: -Si(OR)3 - where R can be H, C1-C3 alkyl or Na - attached to a broad class of polymers. Using this material at a dose of 2CH40 ppm minimises scaling on the surface of the heat exchangers. The disadvantages of the reagent include the inability to modify the heating surface to give it hydrophobic properties.

Heitner et al., 2014, Hydrophobically modified polyamine scale inhibitors, US 9,365,442 B2, discloses that the developers add new properties to sodalite scaling inhibitors by introducing into the structure a wide range of hydrophobicity modifiers that are attached to a reactive secondary nitrogen atom contained in the polymerization reaction product - branched polyamine. The main disadvantage of this disclosure is considered to be the increased kinematic viscosity of the reagent, which increases due to the use of polymerisation products with a relatively high molecular weight during the synthesis of the final reagent. As a result, this leads to poor distribution of the reagent in aluminate solutions.

US14/151,368 discloses a composition that inhibits sodalite scaling, which has no disadvantage of kinematic viscosity. According to this patent document, the product of nonpolymerization reaction of a number of substances is used as an inhibitor, namely: low molecular weight binding amine; substances with one amine-reactive functional group and another silane-reactive functional group -Si(OR)3 - where R is H, C1-C12 alkyl, aryl, Na, K, Li or NH4; hydrophobic impurities with molecular weight of at least 500 Da from a group of halogenoalkanes C3-C22, phenol glycidyl and C3-C22 glycidyl ether, C3-C22 esters of sulphuric acid or a combination of these compounds. In addition to the advantage of decreasing kinematic viscosity, the authors argue that lower molecular weight provides faster diffusion of the inhibitor and the presence of more active inhibitory substances at the site of formation of SHAS crystals. One of the main disadvantages of this disclosure, as in previous cases, is the lack of efficiency of the reagent during the processing of low-quality bauxite.

RU2678269 discloses a method of obtaining a surfactant to reduce aluminosilicate deposits by adding a non-polymeric product to the spent liquor, obtained by reacting an amine- binding surfactant, selected from linear, branched, aliphatic or cycloaliphatic monoamines, diamines, triamines, butylamines, pentylamines, dodecyl-1,3- propanediamine and also glycidoxy alkyltrimethoxy silane.

However, it is known that in the processing of low-quality bauxite, limestone additions are used in technological processes that include a high share of impurities, which increases silicates, sulphates and carbonates in the spent liquor to values greater than 1.5 g/dm³ in terms of SiCh, 60 and 120 g/dm³, respectively. In addition, particles of aluminium hydrate and red mud residues may enter the technological streams, which in turn can act as centres of scale formation.

US 2014/071798 discloses a method of obtaining a composition of the inhibitor. It includes a surface promoter in the form of unmodified branched polyamine, bifunctional organosilane adhesion enhancer with reactive organic epoxide and hydrolysable inorganic methoxysilyl groups and glycidyl ether as a hydrophobic agent. In addition to the composition of the scale inhibitor, this patent document discloses in full the ways to reduce the possibility of sodalite formation, namely the pre-treatment of heating surfaces with specialized siliconate-type polymers. The main disadvantage of this method is the condition of using the composition on pre-descaled surfaces, which requires treating the surfaces of heat exchangers with a composition that inhibits the formation of solid sediments before the surface comes into contact with the spent liquor flow based on the Bayer process.

Consequently, there is still a need for a method that allows obtaining more efficient composition, which would provide not only protection of heat exchanger surfaces of evaporators from precipitators from the spent liquor with high content of CCh²' and SCU²', and solids (aluminium hydrate, red mud), but could also be used in the current technological flow of the Bayer process for washing heating surfaces on the go.

SUMMARY OF THE INVENTION

An aspect of the present invention provides a composition, for reducing the amount of sodium hydroaluminosilicate deposits on the surfaces of equipment used in the process of alumina production based on the Bayer method, consisting of (in wt. %)

• surface promoter: 7,0 18,0 %, wherein the surface promoter is a complex mixture of modified and unmodified branched polyamines,

• bifunctional organosilane adhesion promoter: 3,0 8,0 %,

• hydrophobic agent: 1,0 6,0 %, wherein the hydrophobic agent is glycidyl ester of synthetic saturated branched tertiary monocarboxylic acid,

• hydrotrope and dispersant agents: 1,0 10,0 %, wherein the hydrotrope and dispersant agents are non-ionic surfactants C4-C12 alkylpolyglucosides, and/or cationic surfactants Cio-Cis alkyldimethylaminoxides,

• chelating agent: 0,5 3,0 %, wherein the chelating agent is selected from the group comprising HEDP (1-Hydroxy Ethylidene-l,l-Diphosphonic Acid), DETMPA (Diethylene Triamine Penta Methylene Phosphonic Acid), and PAPEMP (Polyamino Polyether Methylene Phosphonic Acid),

• polar solvent: q.s. ad 100%.

Another aspect of the present invention provides a method of obtaining a composition for reducing the amount of sodium hydroaluminosilicate desposits on the surfaces of equipment used in the process of alumina production based on the Bayer method, wherein the method consists in mixing and dissolving in a polar solvent, while maintaining conditions of normal pressure and temperature, compounds selected from the group consisting of surface promoter, wherein the surface promoter is a complex mixture of modified and unmodified branched polyamines,

- bifunctional organosilane adhesion promoter,

- hydrophobic agent, wherein the hydrophobic agent is glycidyl ester of synthetic saturated branched tertiary monocarboxylic acid,

- hydrotrope and dispersant agents in the form of non-ionic surfactants C4-C12 alkylpolyglucosides, and/or cationic surfactants Cio-Cis alkyldimethylaminoxides,

- chelating agent, wherein the chelating agent is selected from the group comprising HEDP (1-Hydroxy Ethylidene-l,l-Diphosphonic Acid), DETMPA (Diethylene Triamine Penta Methylene Phosphonic Acid), and PAPEMP (Polyamino Polyether Methylene Phosphonic Acid), wherein said compounds are added at the following ratio, weight %: surface promoter: 7,0 18,0 % adhesion promoter: 3,0 8,0 %

- hydrophobic agent: 1,0 6,0 %

- hydrotrope and dispersant agents: 1,0 10,0 %

- chelating agent: 0,5 3,0 %

- polar solvent: q.s. ad 100%.

DETAILED DESCRIPTION OF THE INVENTION

All publications, patent applications, patents, and other references mentioned herein are incorporated by reference in their entirety. The publications and applications discussed herein are provided solely for their disclosure prior to the filing date of the present application. Nothing herein is to be construed as an admission that the present invention is not entitled to antedate such publication by virtue of prior invention. In addition, the materials, methods, and examples are illustrative only and are not intended to be limiting.

In the case of conflict, the present specification, including definitions, will control. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as is commonly understood by one of skill in art to which the subject matter herein belongs. As used herein, the following definitions are supplied in order to facilitate the understanding of the present invention. The term “comprise” is generally used in the sense of include, that is to say permitting the presence of one or more features or components. Also as used in the specification and claims, the language "comprising" can include analogous embodiments described in terms of "consisting of “ and/or "consisting essentially of’.

As used in the specification and claims, the singular form "a", "an" and "the" include plural references unless the context clearly dictates otherwise.

As used in the specification and claims, the term "and/or" used in a phrase such as "A and/or B" herein is intended to include "A and B", "A or B", "A", and "B".

As used herein, the term “at least one” means “one or more” and also encompasses the terms “at least two”, “at least three”, “at least four”, etc.

As used herein, the term "q.s. ad" refers to addition of a sufficient quantity of that material / compound to bring the final composition to the specified volume.

The present invention aims to develop more efficient composition and a method for obtaining thereof, which would provide not only protection of heat exchanger surfaces of evaporators from precipitators from the spent liquor with high content of CCh²' and SC ²', and solids (aluminium hydrate, red mud), but could also be used in the current technological flow of the Bayer process for washing heating surfaces on the go.

An aspect of the present invention provides a composition, for reducing the amount of sodium hydroaluminosilicate deposits on the surfaces of equipment used in the process of alumina production based on the Bayer method, comprising (in wt. %) or consisting of (in wt. %)

• surface promoter: 7,0 18,0 %, preferably 9,0 - 11,0 %, wherein the surface promoter is a complex mixture of modified and unmodified branched polyamines,

• bifunctional organosilane adhesion promoter: 3,0 8,0 %, preferably 4,0 - 6,0 %,

• hydrophobic agent: 1,0 6,0 %, preferably 2,0 to 4,0 %, wherein the hydrophobic agent is glycidyl ester of synthetic saturated branched tertiary monocarboxylic acid, • hydrotrope and dispersant agents: 1,0 10,0 %, preferably 5,0 - 8,0 %, wherein the hydrotrope and dispersant agents are non-ionic surfactants C4-C12 alkylpolyglucosides, and/or cationic surfactants Cio-Cis alkyldimethylaminoxides,

• chelating agent: 0,5 3,0 %, preferably 1,0 - 2,0 %, wherein the chelating agent is selected from the group comprising HEDP (1-Hydroxy Ethylidene-l,l-Diphosphonic Acid), DETMPA (Diethylene Triamine Penta Methylene Phosphonic Acid), and PAPEMP (Polyamino Polyether Methylene Phosphonic Acid), preferably the chelating agent is PAPEMP (Polyamino Polyether Methylene Phosphonic Acid),

• polar solvent: q.s. ad 100%.

In a preferred embodiment, the present invention provides a composition, for reducing the amount of sodium hydroaluminosilicate deposits on the surfaces of equipment used in the process of alumina production based on the Bayer method, consisting of (in wt. %)

• bifunctional organosilane adhesion promoter: 3,0 8,0 %, preferably 4,0 - 6,0 %

• hydrophobic agent: 1,0 6,0 %, preferably 2,0 - 4,0 %, wherein the hydrophobic agent is glycidyl ester of synthetic saturated branched tertiary monocarboxylic acid,

• hydrotrope and dispersant agents: 1,0 10,0 %, preferably 5,0 - 8,0 %, wherein the hydrotrope and dispersant agents are non-ionic surfactants C4-C12 alkylpolyglucosides, and/or cationic surfactants Cio-Cis alkyldimethylaminoxides,

• polar solvent: q.s. ad 100%.

According to an embodiment of the composition of the invention, the bifunctional organosilane adhesion promoter comprises or consists of reactive organic epoxide and hydrolysable inorganic methoxysilyl groups.

Another aspect of the present invention provides a method for obtaining the composition of the invention for reducing the amount of sodium hydroaluminosilicate deposits on the surfaces of equipment used in the process of alumina production based on the Bayer method, wherein the method comprises or consists in mixing and dissolving in a polar solvent, while maintaining conditions of normal pressure and temperature, compounds selected from the group comprising or consisting of surface promoter, wherein the surface promoter is a complex mixture of modified and unmodified branched polyamines,

- bifunctional organosilane adhesion promoter,

- chelating agent, wherein the chelating agent is selected from the group comprising HEDP (1-Hydroxy Ethylidene-l,l-Diphosphonic Acid), DETMPA (Diethylene Triamine Penta Methylene Phosphonic Acid), and PAPEMP (Polyamino Polyether Methylene Phosphonic Acid), preferably the chelating agent is PAPEMP (Polyamino Polyether Methylene Phosphonic Acid), wherein said compounds are added at the following ratio, weight %: surface promoter: 7,0 18,0 %, preferably 9,0 - 11,0 %, adhesion promoter: 3,0 8,0 %, preferably 4,0 - 6,0 %, hydrophobic agent: 1,0 6,0 %, preferably 2,0 - 4,0 %,

- hydrotrope and dispersant agents: 1,0 10,0 %, preferably 5,0 - 8,0 %,

- chelating agent: 0,5 3,0 %, preferably 1,0 - 2,0 %,

- polar solvent: q.s. ad 100%.

In a preferred embodiment, the present invention provides a method for obtaining the composition of the invention for reducing the amount of sodium hydroaluminosilicate deposits on the surfaces of equipment used in the process of alumina production based on the Bayer method, wherein the method consists in mixing and dissolving in a polar solvent, while maintaining conditions of normal pressure and temperature, compounds selected from the group consisting of surface promoter, wherein the surface promoter is a complex mixture of modified and unmodified branched polyamines,

- bifunctional organosilane adhesion promoter, - hydrophobic agent, wherein the hydrophobic agent is glycidyl ester of synthetic saturated branched tertiary monocarboxylic acid,

- chelating agent: wherein the chelating agent is selected from the group comprising HEDP (1-Hydroxy Ethylidene-l,l-Diphosphonic Acid), DETMPA (Diethylene Triamine Penta Methylene Phosphonic Acid), and PAPEMP (Polyamino Polyether Methylene Phosphonic Acid), preferably the chelating agent is PAPEMP (Polyamino Polyether Methylene Phosphonic Acid), wherein said compounds are added at the following ratio, weight %: surface promoter: 7,0 18,0 %, preferably 9,0 - 11,0 %, adhesion promoter: 3,0 8,0 %, preferably 4,0 - 6,0 %, hydrophobic agent: 1,0 6,0 %, preferably 2,0 - 4,0 %,

- hydrotrope and dispersant agents: 1,0 10,0 %, preferably 5,0 - 8,0 %,

- chelating agent: 0,5 3,0 %, preferably 1,0 - 2,0 %,

- polar solvent: q.s. ad 100%.

In an embodiment of the method of the invention, the mixture of surface promoter, adhesion promoter and hydrophobic agent is pre-thermostated (pre-heated) for 6 to 10 hours (i.e. during minimum 6 hours to maximum 10 hours) at 60°C to 80°C (temperature selected between 60° to 80°C), preferably for 8 hours at 70°C, before adding into said mixture hydrotrope and dispersant agents and chelating agent. The term "pre-thermostated" typically means "preheated" and refers to the mixture that is heated beforehand during desired time at desired temperature, wherein the desired temperature is regulated by a thermostat.

In another embodiment of the method of the invention, the mixture of surface promoter and adhesion promoter is pre-thermostated (pre-heated) for 10 to 14 hours (i.e. during minimum 10 hours to maximum 14 hours) at 40°C to 60°C (temperature selected between 40°C to 60°C), preferably for 12 hours at 50°C, before adding into said mixture hydrophobic agent, hydrotrope and dispersant agents, and chelating agent. The term "pre-thermostated" typically means "pre-heated" and refers to the mixture that is heated beforehand during desired time, at desired temperature, wherein the desired temperature is regulated by a thermostat. In some embodiments of the method of the invention, "surfaces of equipment" are surfaces inside of heat exchangers which are in contact with spent liquor.

In some embodiments of the composition of the invention and the method of the invention, the polar solvent is a solvent that contains partial positive or negative charges, such as water, aqueous solutions of alkalis and acids, etc., in which the interaction between the solvent and the dissolved component does not lead to chemical changes in the molecular particles of the latter. In some preferred embodiments, the polar solvent is selected from the group comprising water, dimethylformamide (DMF), dimelthylsulfoxide (DMSO), and isopropanol. Most preferably, the polar solvent is water.

In some other embodiments of the method of the invention, the conditions of normal pressure and temperature are typically 22°C to 25°C and 0,9 bar to 1,1 bar.

In some other embodiments of the composition of the invention and the method of the invention, the surface promoter is mixture of linear and branched modified and unmodified polyethyleneimine with molecular weight from 500 to 2 000 000 Da, such as polyethyleneimine (EPOMIN ™).

In some other embodiments of the composition of the invention and the method of the invention, the bifunctional organosilane adhesion promoter is selected from the group comprising 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropyltriethoxysilane, 2-(3,4- epoxycyclohexyl)ethyltriethoxysilane, [2-(3,4-epoxycyclohexy)ethyl]trimethoxysilane.

In some other embodiments of the composition of the invention and the method of the invention, the hydrophobic agent is glycidyl ester of synthetic saturated monocarboxylic acid of highly branched CIO isomers; preferably the hydrophobic agent is Cardura™ E10P. Cardura E10P monomer is the glycidyl ester of neodecanoic acid (Versatic™ Acid 10), a highly branched carboxylic acid containing 10 carbon atoms.

In some other embodiments of the composition of the invention and the method of the invention, the hydrotrope agent is selected from the group comprising C4-C12 alkylpolyglucosides, such as decyl octyl glycosides (example, Glucopon™ 100DK, Glucopon™ 225DK, Glucopon™ 215UP) and the dispersant agent is selected from the group comprising Cio-Cis alkyldimethylaminoxides, such as lauramine oxide, cocamidopropyl amine oxide (example, EMPIGEN® OB, EMPIGEN® OS/A). Preferably, the hydrotrope agent is C4-C12 alkylpolyglucoside. Preferably, the dispersant agent is Cio-Cis alkyldimethylaminoxide.

In some other embodiments of the composition of the invention and the method of the invention, the chelating agent is selected from the group comprising HEDP (1-Hydroxy Ethylidene-l,l-Diphosphonic Acid), DETMPA (Diethylene Triamine Penta Methylene Phosphonic Acid), and PAPEMP (Polyamino Polyether Methylene Phosphonic Acid).

The present invention provides a method of synthesis a composition for reducing sodium hydroaluminosilicate deposits on the surfaces of the Bayer process equipment (such as surfaces inside of heat exchangers which are in contact with spent liquor) in production alumina, which consists essentially of mixing and dissolving in a polar solvent of surface promoter, which is a complex mixture of modified and not modified branched polyamines, adhesion promoter, such as bifunctional organosilane with reactive organic epoxide and hydrolysable inorganic methoxysilyl groups, hydrophobic agent (hydrophobisier) such as glycidyl ester of synthetic saturated monocarboxylic acid, hydrotrope and dispersant agents such as non-ionic surfactants, from group C4-C12 alkylpolyglycosides, and cationic surfactants, from group Cio-Cis alkyldimethylaminoxides (alkyl dimethyl oxides with Cio-Cis compounds), and chelating agent such as polyamino polyether methylene phosphonic acid, in the following proportion of compounds, weight % (wt. %) (mass. %): surface promoter 7,0-48,0; adhesion promoter 3, 0^-8, 0; hydrophobic agent l,04>,0; hydrotrope and dispersant agents 1,0-40,0; chelating agent 0,543,0; polar solvent q.s. 100%. In an embodiment, the mixture of the surface promoter, adhesion promoter and hydrophobic agent is prethermostated for 8 hours at 70°C, before adding the hydrotrope and dispersant agents and a chelating agent. In another embodiment, the mixture of the surface promoter and adhesion promoter is pre-thermostated for 12 hours at 50°C, before the mixture of hydrotrope and dispersant agents, chelating agent and hydrophobic agent is added to them.

Distinctive features of the composition of the present invention and the method of the present invention are the use of surface promoter as complex mixture of modified and not modified branched polyamines and glycidyl ester of synthetic saturated monocarboxylic acid as hydrophobic agent (hydrophobisier). Also, the presence of new components - mixture of non- ionic surfactants from group C4-C12 alkylpolyglycosides, and cationic surfactants from group C10-C18 alkyldimethylaminoxides, which are used as hydrotrope and dispersant agents, as well as polyamino polyether methylene phosphonic acid used as chelating agent in following proportion of compounds, weight % (wt. %) (mass. %): surface promoter 7,0-48,0; adhesion enhancer 3, 0^-8, 0; hydrophobic agent 1, 045,0; hydrotrope and dispersant agents 1, 0-40, 0; chelating agent 0,543,0; polar solvent q.s. 100%. That is, a distinctive feature of the invention is that the composition and the method for obtaining the composition has a different set of suitable components (substances) in a specific ratio, which are mixed together in a certain sequence, and special processing. In an embodiment, the mixture of the surface promoter, adhesion enhancer and hydrophobic agent is pre-thermostated for 8 hours at 70°C, before adding the hydrotrope and dispersant agents and the chelating agent. In another embodiment, the mixture of the surface promoter and adhesion enhancer is pre-thermostated for 12 hours at 50°C, before the mixture of hydrotrope and dispersant agents, chelating agent and hydrophobic agent is added to them.

The technical result and advantage of the composition of the present invention and of the method of the present invention is that the resulting synthesised composition of the invention and specific ratios of components, provide the lowest required dosage of the reagent, in other words results in greater efficiency of inhibition of scaling, unattainable with similar methods of the prior art.

The ratio of components in the composition ensures the stability and efficiency of the process of evaporation of the spent liquor of the Bayer process in a significantly wider range of concentrations of pollutants.

The introduction of a mixture of hydrotrope and dispersant agents and chelating agent increases the degree of inhibition of SHAS at high concentrations of solids in the spent liquor, and the specified amount of 5%, 3% and 1% by weight respectively, provide the highest efficiency with a minimum amount of reagent consumption.

Experiments have shown that the introduction of 10% of the mixture hydrotrope and dispersant agents with the addition of a chelating agent to the composition inhibits the formation of SHAS by an average of 964)8% while reducing costs by 3 5%. At the same time, its introduction in smaller quantities does not ensure the achievement of such indicators, and its introduction in larger quantities practically does not increase this degree. The ratio of components in the composition (hydrotrope and dispersant agents, and chelating agents) ensures the stability and efficiency of the evaporation of the spent liquor in a much wider range of pollutant concentrations and facilitates the possibility of cleaning the heating surfaces process equipment in real time.

Thus, each individual feature and the set of features of the proposed composition is aimed at solving the problem of creating effective protection of heat exchange surfaces of evaporators in the technological processes of alumina production.

Comparative analysis of the present invention with the similar methods of the prior art allows to conclude that all of the key stated indicators are superior.

Those skilled in the art will appreciate that the invention described herein is susceptible to variations and modifications other than those specifically described. It is to be understood that the invention includes all such variations and modifications without departing from the spirit or essential characteristics thereof. The invention also includes all of the steps, features, compositions and compounds referred to or indicated in this specification, individually or collectively, and any and all combinations or any two or more of said steps or features. The present disclosure is therefore to be considered as in all aspects illustrated and not restrictive, the scope of the invention being indicated by the appended claims, and all changes which come within the meaning and range of equivalency are intended to be embraced therein.

The foregoing description will be more fully understood with reference to the following Examples. Such Examples, are, however, exemplary of methods of practising the present invention and are not intended to limit the application and the scope of the invention.

EXAMPLES

Examples of obtaining the composition and its application.

The composition was obtained as follows: The components were selected based on the inventors' knowledge, mixed and subjected to thermostating (a procedure, which involves maintaining a constant temperature for some time to increase the reaction rate). Then the selected components were added and mixed again, after which the total obtained new mixture was dissolved in a polar solvent (these are solvents that contain partial positive or negative charges, such as water, aqueous solutions of alkalis and acids, etc., in which the interaction between the solvent and the dissolved component does not lead to chemical changes in the molecular particles of the latter). The solvent was added after mixing all the components. Separately, for comparative tests, a composition was prepared according to a similar method of the prior art.

Example 1

The composition was obtained as follows. The mixture of the surface promoter, adhesion enhancer and hydrophobic agent was pre-thermostated for 8 hours at 70°C, after which a mixture of hydrotrope and dispersant agents and a chelating agent were added in and dissolved. The amount of additives was added so that the mixture of alkylpolyglucoside, alkyldimethylaminoxide and polyamino polyether methylene phosphonic acid was 5%, 3% and 1% by weight respectively. Afterwards, dissolution was performed. The resulting composition was added to spent liquor with dosage of 5-^20 ppm for the industrial production of alumina.

Example 2

The composition was obtained as follows. The mixture of the surface promoter and adhesion enhancer was pre-thermostated for 12 hours at 50°C, before the mixture of hydrotrope and dispersant agents, chelating agent was added to them. The amount of additives (hydrotrope and dispersant agents and chelating agent) was added so that the mixture of alkylpolyglucoside, alkyldimethylaminoxide and polyamino polyether methylene phosphonic acid was 5%, 3% and 1% by weight respectively. Then the hydrophobic agent was added in an amount corresponding to the content of glycidyl ester of synthetic saturated monocarboxylic acid - 1% by weight. This specific technological operation allows to modify the entire surface of the formed branched molecule. Afterwards, dissolution was performed. The resulting composition was added to spent liquor with dosage of 5-^20 ppm for the industrial production of alumina.

The efficiency of the obtained composition was evaluated by the results of industrial comparative tests in the technological process of alumina production based on the Bayer process, where the quantitative criterion was chosen to be an interval (duration) between cleaning evaporators, steam pressure and a heat transfer coefficient (HTC). The results of the composition obtained by the method of the present invention were compared to the prior art.

The results obtained are shown in the Table 1 below.

Table 1. The interval between cleaning based on the condition of adding the proposed composition to the spent liquor in the technological process of alumina production based on the Bayer process (dose 20 ppm).

* The test period was completed when steam pressure reached 4,5 bar or HTC lower 1450 kcal/(m²xhxs).

The tests showed that the use of the composition obtained by the invention allows to increase the interval between cleaning procedures from 120 to 165 days, increase production capacity by 7%, reduce the specific energy consumption for evaporation of excess water from the spent liquor by 9% and also increase the concentration of the mother liquor by Na?O by about 2,5%.

Based on the above, it is possible to conclude that the composition obtained by the method of the present invention can be used on known and widespread equipment in the mining industry using proven technologies and using materials that are not scarce or difficult to access.

Claims

1. A composition, for reducing the amount of sodium hydroaluminosilicate deposits on the surfaces of equipment used in the process of alumina production based on the Bayer method, consisting of (in wt. %)

• bifunctional organosilane adhesion promoter: 3,0 8,0 %,

• polar solvent: q.s. ad 100%.

2. The composition of claim 1, wherein the bifunctional organosilane adhesion promoter comprises reactive organic epoxide and hydrolysable inorganic methoxysilyl groups.

3. A method for obtaining a composition of claims 1-2, wherein the method consists in mixing and dissolving in a polar solvent, while maintaining conditions of normal pressure and temperature, of compounds selected from the group consisting of surface promoter, wherein the surface promoter is a complex mixture of modified and unmodified branched polyamines,

- bifunctional organosilane adhesion promoter,

- hydrotrope and dispersant agents in the form of non-ionic surfactants C4-C12 alkylpolyglucosides, and/or cationic surfactants Cio-Cis alkyldimethylaminoxides, - chelating agent, wherein the chelating agent is selected from the group comprising HEDP (1-Hydroxy Ethylidene-l,l-Diphosphonic Acid), DETMPA (Diethylene Triamine Penta Methylene Phosphonic Acid), and PAPEMP (Polyamino Polyether Methylene Phosphonic Acid), wherein said compounds are added at the following ratio, weight %: surface promoter: 7,0 18,0 % adhesion promoter: 3,0 8,0 %

- hydrophobic agent: 1,0 6,0 %

- hydrotrope and dispersant agents: 1,0 10,0 %

- chelating agent: 0,5 3,0 %

- polar solvent: q.s. ad 100%.

4. The method of claim 3, wherein the mixture of surface promoter, adhesion promoter and hydrophobic agent is pre-thermostated for 6 to 10 hours at 60°C to 80°C, preferably 8 hours at 70°C, before adding into said mixture hydrotrope and dispersant agents and chelating agent.

5. The method of claim 3, wherein the mixture of surface promoter and adhesion promoter is pre-thermostated for 10 to 14 hours at 40°C to 60°C, preferably 12 hours at 50°C, before adding into said mixture hydrophobic agent, hydrotrope and dispersant agents, and chelating agent.