V.V. Smolyaninov, G.V. Shekhvatova

Research and Production Company “Gamma”, Pushchino, Institutskaya st., 4, Moscow region, Russia, 142290

Gold leaching by polythionates

Biological leaching of gold degrades sulfides, and gold particles become accessible for such leaching agents as cyanides, thiourea, thiosulfates and others. Today, leaching by cyanides represents the main procedure of gold extraction from ores both in traditional technology and in hydrometallurgy. We proposed to apply organic base polythionates as new chemical compounds for eluting a gold-containig complex from a sorbing agent.

According to evaluations of the “Infomine” research group [1], sodium cyanide consumption in the Russia gold-extractive industry is of 250 to 300 tons per ton of native gold, and in 2009 it was as high as 33.3 thousand tons. It is to remind that hydrocyanic acid, the main component of the process, represents one of the most powerful and fast-acting poisons with general toxic effects, its lethal dose is about 0.05 g. Altogether, the gold-extractive industry of Russia consumes 80,000 tons of chemical agents.

The world is intensively searching for processes of using thiosulfates as leaching agents for gold recovery. Depending on the composition of ores and leaching solutions, the gold recovery ratio is 50-96%. The resulting very tough thiosulfate complex is recovered from the pulp by sorbtion on ion-exchangers and by sorbing agent separation, the gold-thiosulfate complex being eluted by polythionates (see US Patent No. 6344068) [2] that are produced with the use of iodine, bromine, hydrogen peroxide as oxidants. Minor residual amounts of iodine and bromine cause very high corrosion of production equipment.

The patent application PCT/AU 2007/00070 of 22.05.2007 [3] discloses that salt mixtures elute the thiosulfate-gold complex from ion-exchangers with higher efficiency but the concentrations are minimum if the mixture contains a trithionate.

We propose to use salt mixtures (mainly thiosulfates) as leaching agents and organic salts of polythionic acids for eluting from an ion-exchange sorbing agent. For the first time in scientific literature, organic bases polythionates were used as an independent group of chemical compounds amongst salts of polythionic acids and of organic bases, mainly onium bases [4]. The term of organic base polythionates exists in Internet since 2010 under the form of two RU Patents No. 2385959 and No. 2404948 [5,6]. According to our last mentioned patent, the

method of obtaining organic base polythionates does not have any analogs or prototypes.

The reaction of forming triethylammonium tetrathionate with the use of triethylamine, SO₂ and H₂S was first described in chemical literature (Smolyaninov reaction).

Replacing chemical agents used in leaching by cyanides with those used in thiosulfate leaching gives much lower cost and higher security of the process, the production equipment being used for its whole predetermined life.

Production waste represents sulfur-containing nontoxic compounds similar to mineral fertilizers.

It was proposed to use polythionates as efficient gold eluting agents from an anion exchanger, after leaching with a thiosulfate [2,3]. Thiosulfate leaching of gold represents a potentially attractive alternative to a respective cyanation process, at least for three types of auriferous ores. Firstly, in auriferous ores containing an organic carbon material, the recovery of gold by thiosulfate leaching is generally significantly higher due to the insensibility of the thiosulfate complex of gold to the preg robbing. In the second place, gold/copper containing ores often are not convenient for the cyanation process due to high cyanide consumption by copper in the ore, which leads to an unacceptably high cost. Thiosulfate does not easily react with copper minerals, and the lower reagent cost and the lower sulfate consumption compared to cyanides lead to a lower cost in such a situation. And finally, there are some layers of auriferous ore that cannot be treated by cyanation for being in a delicate environment. The thiosulfate leaching reduces the load onto environment since the chemical reagents used in this process are already used in agriculture.

We proposed to apply organic base polythionates for eluting a gold-containing complex from a sorbing agent [4,5].

Method of gold recovery from sulfide auriferous ores [5]. The invention relates to the method of gold recovery from powdered sulfide auriferous ores after their unlocking by bacterial leaching or by oxidation roasting, or by autoclave oxidation. The method comprises leaching with a solution of a mixture of sodium and ammonium hydrosulfite and thiosulfate, by sorption of the thiosulfate-gold complex on a highly basic anion exchanger and by isolation of the highly basic anion exchanger, the sorption being carried out 2-10 hours after the leaching. Then the thiosulfate-gold complex is eluted with a solution of organic and inorganic base polythionates with concentration of 0.2 to 10%. Gold is isolated from the gold-containing eluate by a decomposition reaction or by an electrochemical method. In this case, the decomposition reaction is performed with such metals as magnesium, zinc or iron, or with sulfides. Then the highly basic anion exchanger is regenerated with a solution of a mixture of sodium and ammonium sulfite and sulfate. After the highly basic anion exchanger regeneration, it is transferred to the process of the thiosulfate-gold complex sorption. The technical advantage resides in a faster leaching, a higher gold yield and a lower consumption of the leaching agent.

Method of obtaining organic base polythionates [6]. The invention relates to a method of obtaining organic base polythionates used as fungicides, leveling agents in electrochemical machining of magnesium alloys, for machining stainless and high-alloy steels, for biological hydrometallurgy processes. It is impossible to obtain polythionates well soluble in water, by known processes, since for a successful process run, it is necessary for the organic base to have at least one aliphatic radical with the carbon atom number of at least 7. It is propose a method of obtaining organic base polythionates, in which the organic base solution in an organic solvent is treated with sulfurous gas and later by hydrogen sulfide. After separating precipitated sulfur and distilling off the organic solvent, the organic base polythionate is recovered. No limitations exist for the organic base structure in this case.

In the general formula, the reaction to form organic base polythionates (Smolyaninov reaction) can be given as follows:

2 R₁R₂R₃N + 3 SO₂(gas) + H₂S(gas) → (R₁R₂R₃N)₂H₂S₄O₆ ,

where R₁R₂R₃ are hydrocarbon radicals, С₁ –С₁₈ ;

N represents both ammonium and other onium bases.

In a particular case, while using triethylaimines

2(C₂H₅)₃N + 3SO₂ + H₂S = [(C₂H₅)₃N]₂ . H₂S₄O₆,

the reaction gives colorless oily liquid very similar to glycerol.

Since the structure of the polythionic acid depends on the base structure, the number of sulfur atoms can be different, i.e. 3,5,6, etc.

In scientific and technical literature, this equation is given for the first time.

REFERENCES

1. Ogrel L. (2010). Tendency and specifity of chemical reagents using by gold mining enterprises of Russia. “Zoloto I Tekhnologii”, No. 3(10), pp.. 46-49.

2. C.Fleming et al. Process for recovering gold from thiosulfate leach solutions and slurries with ion exchange resin. US patent No. 6344068, February 2002.

3. J.Matthew. Process for recovering metals from resins. International Application No. PCT/AU2007/00070, 22.05.2007.

4. Smolyaninov V.V., “Electrophoresis and Thin-Layer Chromatography of Organic Base Polythionates”, J. Chromatography, 53 (1970) 337-343.

5. Smolyaninov V.V., Shekhvatova G.V., Smagin V.A. “Method for recovering gold from sulfide auriferous ores”, RU Patent No. 2385959, priority of 28.10.2008, published 10.04.2010, Bulletin No. 10.

6. Smolyaninov V.V., Shekhvatova G.V., Smagin V.A. “Method of obtaining organic base polythionates”, RU Patent No. 2404948, priority of 12.09.2008, published 27.11.2010, Bulletin No. 33.