GROWING ROLE OF ION-EXCHANGE SORBENTS IN THE EXTRACTION OF NON-FERROUS, PRECIOUS AND RARE METALS

ABSTRACT

In recent years, the metallurgical industry has been developing at an accelerated pace in the world. There is a particular tendency towards the comprehensive processing of raw materials and waste from the metallurgical industry and the involvement of metallurgical waste in production. The output of pure and ultra-pure metals is increasing due to the introduction of technology for the selective extraction of useful components into a solution, precipitation or extraction of ultra-pure salts from them. This direction is developing very rapidly in the metallurgy of non-ferrous, noble and rare metals, since obtaining pure and ultra-pure metals at the final stage is very important. Recently, specially developed ion-exchange resins capable of selectively extracting metal from solutions and pulp have been widely used in the metallurgy of noble and rare metals [1].

One of the main tasks facing the country's economy is the mobilization of secondary resources, their more complete and comprehensive use. This task should be considered as an integral part of the global problem of environmental protection, since Almost 90% of the raw materials, annually renewed and extracted from the bowels of the planet, go to waste, polluting the biosphere. That is why our attention was focused on finding ways of complex use of natural resources, creation of effective composite chemical reagents - sorbents (ion exchange resins) with rational use of secondary raw materials, ensuring complete extraction of noble and rare metals from pulp.

Currently, ion exchange resin (composite chemical reagent - sorbent) is widely used in metallurgy of non-ferrous, noble and rare metals.

АННОТАЦИЯ

В последние годы в мире металлургическая промышленность развивается ускоренными темпами. Особенно идет тенденция к комплексной переработке сырья и отходов металлургической промышленности и вовлечению в производство отходов металлургической промышленности. Увеличивается выпуск чистых и особо чистых металлов за счет внедрения технологии селективного извлечения полезных компонентов в раствор, осаждения или извлечения из них особо чистых солей. Это направление очень быстрыми темпами развивается в металлургии цветных, благородных и редких металлов, так как получение в конечном этапе чистых и особо чистых металлов очень актуально. В последнее время для селективного извлечения металлов из растворов и пульпы в металлургии благородных и редких металлов широко применяются специально разработанные ионообменное смолы, способные селективно извлекать металл из растворов и пульпы [1].  Одной из основных задач, стоящих перед экономикой страны, является мобилизация вторичных ресурсов, их более полное и всестороннее использование. Эту задачу нужно рассматривать как составную часть глобальной проблемы охраны окружающей среды, т.к. почти 90% сырья, возобновляемого ежегодно и извлекаемого из недр планеты, идёт в отходы, загрязняющих биосферу. Именно поэтому наше внимание было направлено на поиски путей комплексного использования природных ресурсов, создания эффективных композиционных химических реагентов – сорбентов (ионообменные смолы) с рациональным использованием вторичного сырья, обеспечивающие полное извлечения благородных и редких металлов из пульпы.

В настоящее время ионообменная смола (композиционный химический реагент – сорбент) широко применяется в металлургии цветных, благородных и редких металлов. 

Keywords: ion exchange sorbent, anionite, pulp, precious metals, rare metals, gold, molybdenum, copper, macroporous structure, metallurgical industry, man-made waste.

Ключевые слова: ионообменный сорбент, анионит, пульпа, благородные металлы, редкие металлы, золота, молибден, медь, макропористая структура, металлургическая промышленности, техногенные отходы.

Research results and discussion. Analysis of existing sorbents for the extraction of precious metals.

Ionites are solid, practically insoluble substances or materials capable of ion exchange. Ionites can absorb positive or negative ions (cations or anions) from solutions of electrolytes (salts, acids, and alkalis), releasing an equivalent amount of other ions with a charge of the same sign into the solution instead of the absorbed ones. The molecular structure of an ionite can be represented as a spatial grid or lattice carrying fixed ions, the charge of which is compensated by oppositely charged mobile ions, the so-called counterions.

A distinction is made between polydisperse (Figure 1) granules (the particle size varies in the range of 0.3-1.2 mm) and monodisperse (Figure 2) granules (the particle size is usually 0.5-0.6 mm ± 0.05 mm).

Figure 1. Granules (the particle size varies in the range of 0.3-1.2 mm)

Figure 2. Granules (the particle size is usually 0.5-0.6 mm ± 0.05 mm).

Highly acidic sulfocationites are also obtained by sulfonating styrene copolymers with diisopropenylbenzene, which provides polymer matrices of an isoporous structure.

Copolymerization of methacrylic acid with divinylbenzene resulted in KB-1 cationite.

However, the resulting cationite has a low mechanical strength, and the suspension copolymerization process itself is difficult to control due to the solubility of methacrylic acid in the dispersed phase.

During copolymerization of the methyl ester of acrylic acid with divinylbenzene, the ether unitsare connected in the polymer in the "head-to-head"position. After their saponification, KB-2 cationite has the following structure:

Due to this arrangement of carboxyl groups, the cationite becomes selective with respect to divalent cations.

Polymerization-type anionites

 Anionites ofpolymerization type are obtained by copolymerization of initial monomers that contain ionic groups with dienes and polymeranalogical transformations of styrene copolymers with divinylbenzene or other copolymers that do not contain ionic groups.

Styrene and divinylbenzene are mainly used as raw materials in the productionof polymerization-type anionites.стирол и Copolymerization of styrene with divinylbenzenes occurs by the following reaction.

Сополимер The styrene copolymer with divinylbenzene is chloromethylated with monochlorodimethyl ether, which is obtained by the interaction of methyl alcohol, formalin and hydrogen chloride.

Highly basic anionites are obtained by reacting a chloromethylated styrene -divinylbenzene copolymer with tertiary amines, phosphines, and disulfide.

In recent years, the monomer 2 - methyl-5-vinylpyridine has been increasingly used for the synthesis of weakly-and strongly-basic anion compounds:

В качестве сшивающих агентов divinylpyridine, triethylene glycol dimethacrylate, and diisopropenylbenzene are also used as crosslinking agents in the preparation of anionites.

Depending on the application, polymerization-type anionites can be obtained on the basis of the gel and macroporous structures of the initial copolymer.

Highly basic anionites. Styrene-divinylbenzene copolymers are most widely used in the production of highly basic polymerization-type anionitesе применение находят сополимеры стирола с. Nitrogen-containing anionites obtained on their basis are characterized by high mechanical strength and chemical resistance. Ionic groups of anionite that are rigidly bound to the polymer molecular network, are usually represented by alkyl-substituted ammonium hydroxyl derivatives. Thus, these anionites are a peculiar group of high-molecular quaternary ammonium bases or their salts. Macromolecules of strongly basic anionites may contain a certain number of weakly basic groups.

Highly basic anionites can also be obtained by N-alkylation of vinylpyridine (or vinylquinoline) copolymers with divinyl monomers and copolymerization of onium salts with divinyl monomers.

In addition to the ion-exchange materials discussed above, there is a wide range of products, the method of obtaining which depends on the purpose of a particular polymer compound and the required properties.

The table below shows the grades of some ion-exchange resins.

Table 1.

Brands of ion-exchange resins

Composition and properties of ion-exchange sorbents. Ion exchange is widely used in the technology of chemical separation, extraction, removal, and concentration of non-ferrous metal ions. This is due to the spread of methods using various ion-exchange resins, which are indispensable in many areas of the chemical and metallurgical industries. Ion-exchange sorbents can be used to extract and enrich heavy, noble and rare metals from complex process solutions.

To separate, isolate and extractnon-ferrous, rare and precious metals from solutions of various compositions, sorption is performed using ion exchange resins; VP-14K, VP-10P, VP-1P, AM-2B, KB-4, KU-1. 

Anion exchanger was obtained by the method [2] of chemical modification of chlorinated polypropylene with polyethylenepolyamine. It was found that the chemical structure of the polypropylene macromolecule, which contains up to 15% double bonds, allows for both chemical and thermomechanical modification of the polymer. The kinetics of modified chlorinated polypropylene with polyethylenepolyamine and anion exchange extraction was studied, and it was found that the optimal conditions for carrying out the processes are a temperature of 100° C and a duration of 12 hours. The static exchange capacity (SEC) value of anionite was 4.6 mg-eq/g.

Recently, the developed and introduced (15) ionites based on a copolymer macroporous structure have become widespread. These ionites are characterized by high sorption properties, increased physical and chemical characteristics, and sorption-free schemes of complex ore processing can serve as a rational basis for transferring the experience gained to the hydrometallurgy of non-ferrous, rare and precious metals.

For sorption extraction of largepolymerized molecules, it is more appropriate to use ionites with a porous and macroporous structure. Macroporous ionites containing mainly open pores have a significant void volume, which makes their framework well accessible for the penetration of various ions. Macroporosity increases the volume surface, promotes rapid diffusion of ions and sorption of large molecules. A complex of studies performed under the scientific supervision of Academician B. N. Laskorin made it possible to establish the relationship between sorption properties, the structure of sorbents and the ionic state of metals in solution and to approach the implementation of targeted synthesis of ionites.

As a result of research work [3], the researchers developed medium-basic anion exchange resins VP-1p and VP-14K with a macroporous structure, synthesized on the basis of a copolymer of 2-methyl-5-vinylpyridine with divinylbenzene with the introduction of a pore-forming agent at the synthesis stage. Anionite has a high sorption capacity for metals, chemical resistance to alkalis and acids, and mechanical strength. The kinetics of tungsten absorption from autoclave-soda solutions of sodium tungstite was studied in the region of optimal pH values in the solutionвольфрамита. It is shown that the sorption equilibrium in the sorbent-solution system at various concentrations of tungsten in the initial solution (C_WO3- 40-100g/l) is established in 8 hours. The maximum tungsten absorption capacity reaches 1600 mg/g of the sorbent.

Researchers [4] developed VP-1Ap, VP-3Ap, VP-4Ap, VP-6Ap, and VP-8Ap anionite with a macroporous structure based on 2-methyl-5-vinylpyridine and a volume capacity of 5.2, 5.0, and 5.1 mg-eq/g for the CI^- - ion. Anionites differ in the structure of ammonium groups. The anion group VP-10Ap, VP-11Ap, and VP-12Ap with the same physical-chemical properties was obtained on the basis of 4-vinylpyridine with a macroporous structure and a volume capacity of 5.3, 5, 4, 5, 4 mg-eq/l. Anionites can be used to extract heavy metal ions from acidic environments.

Anionite [5] AMP-p- has a macroporous structure and is intended for use in hydrometallurgy (extraction, separation, concentration of elements for processing solutions and pulps by sorption), as well as in the processes of purification and neutralization of waste and recycled industrial solutions, water treatment, and analytical chemistry.

 A sorbent was obtained [6] for extracting gold ions by aminating chloromethylated porous styrene copolymers with divinylbenzene and polyethylene polyamine in a solvent, and the chloromethylated copolymer has a macro - and mesoporous structure with a predominance of mesopores with diameters of 3-10 nm.

A method was developed [7] for obtaining easily regenerated ionite for gold sorption from cyanide hydrometallurgical media. The copolymer is prepared by suspension polymerization of a mixture of monomers and a pore-forming agent selected from aliphatic carbons.

Researchers [8] B.N. developed anion exchanger AM-2B with a mixed base and macroporous structure. Anionite is used in hydrometallurgy for the extraction and concentration of various elements, in sorption processes from solutions and pulps, and wastewater treatment, industrial and chemical chemistry, etc., and also sorbs cyanide complexes of non-ferrous metals from ore pulps and solutions of complex salt composition, elution of absorbed complexes is effectively carried out by acidic thiourea solutions.

AM-2B anionite is a macroporous ion-exchange resin based on a styrene-divinylbenzene copolymer, containing strong and weakly basic functional groups in its structure. The presence of bifunctional active groups combined with a high exchange capacity and good exchange kinetics makes it possible to selectively extract gold cyanide anionic complexes. The macroporous structure and increased grain size of the working fraction give AM-2B anionite unique properties when used in hydrometallurgy to separate cyanide complexes of non-ferrous and precious metals during sorption from ore pulps of complex salt composition.

• It has high mechanical strength, chemical and osmotic resistance.
• It has high kinetics and selectivity of ion exchange.
• It is easily desorbed and restores its properties during regeneration.
• It is chemically resistant to alkalis, acids, and oxidizing agents.

Table 2.

Basic physical and chemical properties

Anionite is produced according to TU U 24.1-30168850-030:2006.

AM-2B anionite is similar in structure and properties to the following ionites: AN-18p (USSR), zerolite MRN (England), dauex MWA-1 (USA), duolite A-368, A-368Rg, A-369, A-303 (France), amberlight HE-124 (USA).

Researchers [9] developed new granular ionites based on acrylonitrile, divinylbenzene, and N, N'-methylene bis-acrylamide with a given structure and physicochemical properties. The operational capabilities of new granular cationites and weakly basic anionites capable of extracting metal ions and organic compounds from industrial wastewater and other sources due to their ion-exchange and complexing properties are shown.

The above-mentioned ionites can improve the technical and economic indicators of sorption extraction of precious metals from cyanide media.

Application of ion-exchange resins in the extraction of precious metals. Sorption of precious metals by ion-exchange resins can be carried out both from clarified cyanide solutions and directly from pulps during cyanidation. Cyanidation occupies a special place in the gold mining industry and is based on the ability of gold, as well as silver, to dissolve in weak solutions of alkaline cyanides by the reaction:

2Au + 4NaCN + 1/2O ₂ + H₂O = 2Na[Au(CN)₂] + 2NaOH

Gold and silver in cyanide solutions are in the form of complex anions [Au(CN)₂] -, [Ag(CN)₃] -, [Ag(CN)₃]₂-and [Ag(CN)₄]₃-. Therefore, for their sorption, obviously, anionites should be used. Sorption of precious metals from cyanide solutions by anionites can be represented by the following reactions:

where the dash denotes the anionite phase. In addition to gold and silver, a number of complex cyanide anions of base metals are usually present in working cyanide solutions: [Cu(CN)₂]^-, [Cu(CN)₃]₂^-, [Cu(CN)₄]₃^-, [Zn(CN)₃]^-, [Zn(CN)₄]₂^-, [Ni(CN)₄]₂^-, [Co(CN)₆]₄^-, [Fe(CN)₆]₄^- and others, as well as anions CN -, OH -, SCN -, S2-and others, which can also be sorbed by anionites in significant quantities by the reactions:

where n is the valence of the complex anion; m is the coordination number of the metal.

As a result of these reactions, some of the active groups of anionite are occupied by anions of impurities, which significantly reduces the capacity of the resin for precious metals.

The following types of anionites can be used for gold and silver sorption in the cyanide process: 1) strongly basic (domestic brands AM, AB-17, AMP) with functional groups in the form of quaternary ammonium =N+ or pyridine R-N bases with a high degree of dissociation in acidic and alkaline media (pK ≤ 2) and, therefore, showing active ion exchange properties in a wide range of pH values of the medium; 2) weakly basic (brands AN-18, AN-21, AN-31, etc.) with functional groups in the form of primary-_NH3⁺, secondary₂^=NH2+ and tertiary =NH+amino groups, weakly dissociating (pH ≥ 4 ... 9) in neutral and alkaline media; 3 ) anionites mixed basicity — polyfunctional (brands AM-2B, AP-2, AP-3, etc.) containing strong-base (=N+) and weak-base (- NH3+, =NH2+, =NH+) functional groups in various ratios and exhibiting the properties of strong and weak bases with varying ion exchange activity in the following conditions: depending on the pH value of the solution.

In 2000, the cyanide method was used for processing 90-95% of ores in the world, and the share of metal extracted by cyanidation was 80-85% [36].

AB-17 and AM anionites are a chloromethylated styrene copolymer with DBV aminated with trimethylamine N(CH3) 3, of the following structure:

According to I. N. Plaksin and M. S. Girdasov, when sorption from cyanide solutions obtained during leaching of ore from the Baleyekoye deposit (solution composition, mg/l: Au 4.8; Cu 13.6; Zn 28.9; Fe 9.8; Sb 2.9; As 1.8; Sc 185.0; NaSCN 23.6; NaCN 400.0; NaOH 200.0The volume capacity for gold was only 8.9 mg/g (due to the low selectivity of the anion), and the highly basic AB-17 anion in the Cl form. Highly basic anionites can be used for extracting gold and silver from cyanide solutions with a low content of impurities, as well as for cleaning waste water from gold extraction and processing plants from cyanide compounds. Weakly basic anionites with dimethylamine in the main composition sorb noble metal cyanide compounds more selectively, but their total capacity is less than that of strongly basic anionites due to the low dissociation of their active groups in alkaline media. Among domestic weakly basic anionites, AN-18 polymerization - type anionite aminated with N(CH3) dimethylamine showed the best results₃)₂2H and containing as ionic groups a tertiary amine =NH⁺. The capacity of AN-18 anionite in Cl^- and^OH forms during gold sorption from synthetic solutions containing free cyanide and alkali was 94.45 and 95.7 mg / ml, respectively, or about 190.0 mg/g (I. N. Plaksin, M. S. Girdasov). When gold is sorbed with AN-18 anion in OH form from process solutions of complex composition, its gold capacity is 25-50% higher than the capacity.

Among bifunctional anionites, AM-2B of macroporous structure is most widely used. This anionite contains a matrix in the form of a styrene-DVB copolymer treated with chloromethyl ether and aminated with a mixture of secondary and tertiary amines. The resin structure is as follows:

The DVB content is 10-12%. The number of strong-base and weak-base groups is the same - 50% each. Anion AM-2B has a fairly high mechanical strength, increased kinetic properties and is used in industrial cyanidation practice.

AP-2 anion is prepared using methylmethylenediamine as a diamine. The AP-2 structure is as follows:

It exhibits bifunctional properties due to the presence of two ionized groups with different ionization constants in diamines.

Along with the absolute advantages of the sorbents obtained by the methods described above, the experience of their industrial application has revealed a number of problems related to the complexity of regeneration, consisting of eight consecutive operations with a total duration of more than 200 hours, with the transition from alkaline cyanide to acidthiourea treatment, which negatively affects the strength of the sorbents, the release of toxic prussic acid gas, the need for its detoxification and organization of personnel protection measures, the use of expensive acid-resistant equipment and reagents (thiourea). However, the process of sorption of non-ferrous, rare and non-native metal ions from multicomponent solutions and pulps remains insufficiently studied.

In the metallurgical industry, especially in the production of non-ferrous, precious, refractory and rare metals, the main amount of metal is completely extracted using ion-exchange sorbents.

For the gold cyanide complex, a bifunctional macroporous anionic sorbent AM-2B based on styrene and divinylbenzene has been developed as an ion-exchange resin. It is sufficiently durable, easily regenerated, has high capacity and selectivity. The resin consumption is 10-20 g/t. The counterion in resin is the hydroxyl ion ОН ^- which is easily exchanged for the gold-cyanide complex.

The cyanide complex interacts with resin according to the ­following procedure

[Au(CN)₂]^- + ROH = R[Au(CN)₂] + OH^-;

where R is the ionite framework.

Gold recovery from solution is determined by its equilibrium concentration ­in solution. In addition to gold, free cyanide and cyanide complexes of other metals are collected on the resin.

ROH + CN^- = RCN + OH^-;

2ROH + [Zn(CN)₄]^2- = R₂[Zn(CN)₄]+2OH^-;

2ROH + [Cu(CN)₃]^2- = R₂[Cu(CN)₃]+2OH^-

4ROH + [Fe(CN)₆]^4- = R₂[Fe(CN)₆]+4OH^-;

The reactions carried out reduce the resin's gold capacity.  Cl^-, SO4_-, and S2O3 2 - anions are also collected on the resin.-, S2О32- 

For most anionites, the sorption order of complex metal ­anions is as follows:

[Au(CN)₂]^- > [Zn(CN)₄]² > [Ni(CN)₄]^2- >

> [Ag(cn)2]^- > [Cu(CN)₃]^2- > [Fe(CN)₆]^4-

The main factor determining the place of anion in this series is the value of the ion hydration energy: with its decrease, the anion affinity increases. The hydration energy depends on the charge and radius of the ion: as the charge decreases and the radius increases, it decreases. The affinity range of metal anions is the same as the sorption range.

When processing gold-bearing ores with a pH metal content (3-5g/t), the capacity of saturated ionite is in the range of 5-20mg/g. The pulp density in this process is 50-60% solid. The process is carried out at a cyanide concentration of 0.01-0.02 %, i.e. significantly lower than with other cyanide methods. The process is carried out at pH 10-11. As a sorbent, domestic enterprises use macroporous bifunctional anion AM-2B, which has an increased capacity and selectivity to the gold cyanide complex, is easily regenerated, and has high mechanical strength. Ionite consumption is 10-20 g per 1 ton of leached ore.

Conclusion. An analysis of the literature data shows that a large number of studies are currently being conducted on the development of ion-exchange sorbents and technological schemes for the sorption extraction of non-ferrous, precious and rare metals from multicomponent solutions and pulps in metallurgy. In the metallurgical industry, especially in the production of non-ferrous, precious, refractory and rare metals, the main amount of metal is completely extracted using ion-exchange sorbents.

References:

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7. Aksion-Rare and Precious Metals JSC (RU)
8. B. N. Laskorin, G. I. Sadornikov, L. N. Petrova et al., Gold-selective composites.  Journal of Applied Chemistry. 1974. vol. 47, No. 3, pp. 1747-1751.
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10. Open Joint-Stock Company "Leading Research Institute of Chemical Technology "(RU)
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