DD160397A3 - PROCESS FOR PRODUCING PURE GOLD - Google Patents

Abstract

The invention relates to a process for the chemical refining of gold from aqueous solutions. The object and the object of the invention are the development of a method by means of which can be obtained from aqueous solutions of tetrachloroauric acid with metallic impurities gold with high quality and material yield with minimal binding of circulating agents, minimal time, labor and technical effort and low demand excipients. The pure gold representation can be made of gold with metallic trace impurities, but also from heavily contaminated gold. According to the invention, this is achieved by passing a starting solution of tetrachloroauric acid over a prepared cation exchange resin loaded with 0.1 to 1 molar hydrochloric acid at a temperature of 20 to 30 ° C., then purifying out the gold solution with dilute hydrochloric acid and the solution present in the solution Gold is reduced by the addition of reducing agents or electrolytically to the elemental gold.

Description

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Title of the invention

Process for the production of pure gold

Field of application of the invention

The invention relates to a process for the chemical refining of gold from aqueous solutions with metallic impurities by ion exchange.

Characteristic of the known technical solutions

It is known that the enrichment and coarse separation of gold can be realized relatively easily. The removal of trace impurities, however, is very difficult according to electrochemical and physicochemical requirements. For the preparation of gold with a purity of 99.999%, extraction, electrolysis and reprecipitation processes as well as ion exchange methods are already known and also in use.

For example, extraction processes are used to recover gold from its solutions and for refining.

DE-AS 2 031 432 describes a process for the qualitative recovery of gold from aqueous solutions.

The extraction of the gold takes place mainly in the form of the iodide or bromide complex. For extraction

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is ether, "for example, diisopropyl ether, is used. Due to the lower reactivity of iodine and bromine, the the £ ~ AuCl ^ / can" .entspsgehende complex manufacture difficult because much longer reaction times are required.

In addition, "in the extraction process a variety of steps such as dissolution of the gold, conversion into the desired complex, extraction with an organic solvent, separation of the organic phase and evaporation of the solvent, transfer of the dissolved gold into the metal and distillation of the solvents and extractants necessary» prerequisites For such extraction methods, work must be carried out in explosion-proof installations and rooms, and because of the large number of work steps required, they are very labor-intensive and thus also cause higher losses of precious metals.

To obtain gold of the desired purity, electrolysis processes are also known (Gmelin, Verlag Chemie, Weinheim 1954, pp. 338-343). In order to represent pure gold electrolytically, the adherence to low PotentialuntercMed necessary is the result of this little gold is obtained in the unit time Since the refining gold is used as the anode, much material is bound. The technical effort for the extraction of pure gold by these methods, based on the required electrical equipment, is very large.

By repeated reprecipitation (Gmelin, Verlag Chemie, Weinheim 1954, p 346) also a Raffinationsef.fekt can be achieved. For this purpose, the gold is dissolved and precipitated again after filtration of the sparingly soluble constituents. Both processes, loosening and felling occur alternately until the desired effect is achieved. Become impurities of silver and silicon

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separated as silver chloride or as silica. Several days are required to deposit the precipitation. Thus, the reprecipitation procedure is also very time consuming. Failure to meet the given time will result in high silver and silicon gold being recovered. A further disadvantage of this method is that special care must be taken when cleaning the chemicals.

From Metallwissenschaft and Technik, Issue 4, 1978, pp. To 342, the refining of metals by ion exchange is known. However, this is largely limited to the use of anion exchangers that irreversibly bind the gold. For the preparation of the gold, the resin must therefore subsequently ashed and the gold from the ash to be recovered. In addition to the gold, portions of the platinum metals are irreversibly bound, which can not be eluted with hydrochloric acid. The disadvantage of ion exchange methods is that the recovered gold contains carbon and platinum metals and thus this method is only suitable for a coarse separation of the gold from other metals. This requires a further refining of the gold by additional dissolving and falling over. In DE-AS 2 340 157 a combination of PaVLlungs- and ion exchange method has already been proposed. Gold and the contaminating metals are converted into the nitrosochlorides after dissolution in aqua regia. The unelelmetals are then separated by means of cation exchanger. The cation exchange resin has a strong reducing effect owing to its functional structure / The conversion into the nitrosochloride complexes causes a stabilization of the gold complex. It is thereby possible to subsequently pass the gold complex over the ion exchanger without decomposition. Purely nitric acid solutions are used in this process. Hachteilig here is that these nitric acid solutions

ό D

-. ", And the gold complexes in the form of nitrosochlorides

". 'Prevent quantitative precipitation of the gold, as the _V V Nitrosochloride with the respective reducing agent

react, d. H. the solution is "loaded with large amounts of salt or acid because of the need to work with a strong excess of reducing agent." In addition, such solutions must be highly diluted: the overall yield is about $ 60, refining to 99.97% gold. Yield and purity of the gold are considered to be totally unsatisfactory. In some other refining processes already known, the principle of incomplete precipitation is used to obtain material of a desired high purity precipitated and reintroduced into the starting material, thus binding high circulating agents and increasing the absolute rate of loss «,

The disadvantages of already known methods therefore consist mainly in the fact that they require a great technical and high material expenditure

are time-consuming, require a considerable manual use at high circulation costs, cause due to a ^ variety of necessary work steps for the purpose of increasing the purity of the gold increased metal losses and require additional auxiliaries for further refining.

Object of the invention

The aim of the invention is the development of a process for the production of pure gold wit high quality and material yield _s which in comparison to already known methods is little time and labor-consuming, requires little technical effort and low need for Hilfssstöffen'

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and minimum circulating agent binds,

, Explanation of the essence of the invention

The technical object of the invention to be solved is to obtain gold with a purity of 99.999 % quantitatively from aqueous solutions of tetrachloroauric acid with metallic impurities by means of ion exchange.

The impurities in the Gk) Id, the elements Ag, Cu, Fe ₅ Pb, Sn, Ga, Bi, Sb, Si, Pt, Ir, Pd, Rh, Mg, Mn, Gr, Ni, Co, Zn, Al and Y. his.

The process according to the invention envisages using gold to be refined in the form of tetrachloroauric acid, the base metals and precious metal impurities contained in the gold take the form which is stable at the applied ρ value.

To produce the tetrachloroauric acid, gold in the form of sponge, sheet or wire is dissolved in chlorine and hydrochloric acid, the excess hydrochloric acid and the chlorine are evaporated off and a solution is prepared having a gold content of 0.1-0.5 m. The cation exchange resin to be used becomes

prepared by appropriately swelling new resin in the water, regenerating with 5-6M hydrochloric acid, rinsing with water until neutral, and loading with 0.1-1M hydrochloric acid to prevent reduction of the gold by the resin. For the chosen ρ region, which is used to stabilize the gold complex, the impurities are present in the following form:

1, Cu, Ni, Co, Zn, Mn, Cd and Y form simple salts,

2, cationic complexes are preferably formed by Ti, Cr and Al

(Ti / Ti07 ²⁺ , Cr / Cr (H ₂ O) ₄ Cl

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3. Form anionic hexa- or tetrahalogeno complexes

", Ga ³⁺ ZGaCl ^ J",

Sn ⁴⁺ -ZSnCl ₆ J ² ", Pb ²⁺ -ZPbC _{4 6}

Ag ⁺ -ZAgCl ₄ J ³ ".

Of the latter, Sn and Sb form sparingly soluble oxychlorides in the weakly acidic region, Ag precipitates as poorly soluble silver chloride, lead as lead chloride, Bi also forms sparingly soluble oxychloride, and Si is partly present as a colloidal silicate.

4. Common complexes form the platinum metals and tin, The following compounds may occur: ZPtSn ^ Cl ,. c J j

The subsequent to the loading of the resin refining the GoIdIösung \, by passing it at a temperature of 20-30 ⁰ C over the ion exchanger. The gold solution in the ion exchanger, gold is present as an anion and is not bound, is rinsed out with dilute hydrochloric acid.

Despite the different chemical behavior of the individual impurities, formation of anionic complexes and sparingly soluble compounds and joint compound formation, it has surprisingly been found that the abovementioned elements can be satisfactorily depleted in one process step, that is to say they are no longer spectrally analytic detectable.

The impurities bound to the resin are then eluted with 5-6 m hydrochloric acid.

After rinsing the ion exchanger with water and dilute hydrochloric acid, the resin can be reused for refining.

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The gold in the solution is reduced to elemental gold by the addition of reducing agents such as sulphurous acid, hydrogen and hydrazine sulphate or by electrolytic processes.

The traces of gold in the hydrochloric acid used to wash out the gold solution from the resin are also precipitated with known reducing agents. The capacity of the resin depends on the concentration of the gold solution, on the purity of the starting material, ζ. B · 99.96% pure gold and highly contaminated gold, as well as the concentration of hydrochloric acids used to treat the resin. The capacity decreases with increasing hydrochloric acid and increasing gold concentration.

embodiment

The invention will be explained in more detail with some examples.

As a starting material Golä with a purity of 99.96% and 0.04 $ impurities with a temperature of 20 to 30 ⁰ C is used.

example 1

250 ml of a 0.2-mH / ~ AuC! ^ - solution are over 20 ml of cation exchange resin (Wofatit KPS or Wofatit KS 10), which was previously loaded with 0.1-m hydrochloric acid. The R / ~ cation exchange resin contained in the A \ iQL _A J-Tsoe solution is displaced with 0.1 M hydrochloric acid and treating the permeated and displaced hydrochloric acid gold solution with gaseous sulfur dioxide. The reduced gold is washed with distilled water and dried. A spectral analysis revealed that the elements Ag, Cu, Fe, Pb, Sn, Ga, Bi, Sb, Si, Pt, Ir, Rh, Mg, Mn / cr, Hi, P <3, Zn, Al and Y under the required detection limit.

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Example 2

55 ml of a 1, OmH / ~AcCl _4- J solution was added to 20 ml of cation exchange resin loaded with 0.1 M hydrochloric acid. The remaining in the ion exchanger H / "" AuCl, _7 solution is displaced with 0.1-M hydrochloric acid. The complexed gold in the interspersed gold solution and in the hydrochloric acid is reduced by introducing sulfur dioxide. The concentration of all impurities was below the detection limit.

Example 3

500 g of gold were dissolved in hydrochloric acid and chlorine. After evaporation of the excess acid and chlorine, a 0.4 M hydrochloric acid gold solution was prepared. 1 liter of cation exchange resin (KPS or KS 10) was charged with 0.2 M hydrochloric acid, and the solution of tetrachloroauric acid was added to the resin at a rate of 4 L / hr. The hydrochloric acid solution in the column is rinsed out with 0.2 M hydrochloric acid and the gold ions are electrolytically reduced. The elements present in the reduced gold were all below the detection limit.

Example 4

500 g of gold were dissolved in hydrochloric acid and chlorine and a 0.4-m hydrochloric acid gold solution prepared. The ion exchange resin (KPS or KS 10) was charged with 1 M hydrochloric acid. The hydrochloric acid solution was poured over the resin, the gold-containing solutions combined and the gold electrodeposited. After refining, 14 ppm of silver and 8 ppm of silicon were detected by spectral analysis in the gold, which proves that with increasing hydrochloric acid concentration, the impurities are no longer firmly bonded,

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Example *?

200 g of gold are dissolved in hydrochloric acid and chlorine. The hydrochloric acid solution is mixed with 20 g of nickel in the form of nickel chloride, since nickel breaks through all the impurities first. "A 0.4-m hydrochloric acid solution of gold was prepared 0.2 M hydrochloric acid-loaded resin KPS or KS 10. In the reduced gold, no nickel could be detected by spectral analysis.

The proposed method according to the invention is characterized by various advantages compared to previously known solutions. It is essential that by means of this new process with low manual labor and with reduction of precious metal losses, gold with a purity of 99.999% from aqueous solution. can be produced with metallic trace impurities, but also from heavily contaminated gold solutions. At the same time, occupational health and safety is improved by reducing the use of aggressive chemicals. Further advantages of the new method are the minimal outlay on equipment, the reduced amount of auxiliary material and electrical energy as well as a faster throughput and the reduction of circulation costs and the gold stock.

Claims (3)

Erfindunpsanapruch 1. A process for the production of pure gold from aqueous solutions with metallic impurities, wherein the gold to be refined in the form of tetrachloroauric acid is used and passed through an ion exchanger, characterized in that the neutral cation exchange resin before passing the gold to be refined solution with 0.1 to 1 -m hydrochloric acid is loaded. 2. The method according to item 1, characterized in that the gold solution contained in the ion exchanger rinsed out with dilute hydrochloric acid and the gold in the solution is reduced by the addition of reducing agents or electrolytically to $ oil. 3. The method according to item 1, characterized in that the base metals present as cations are eluted with 5 to 6-m hydrochloric acid.