RU2149909C1 - Method of gold recovery from gold-containing materials - Google Patents

Abstract

FIELD: gold hydrometallurgy. SUBSTANCE: method is used in recovery of gold from wastes, secondary materials and electronic scrap with the help of aqua regia. In treatment of gold-containing materials in pickling baths, formed gas-air mixture is subjected to successive passage through alkaline liquor, layer of steel chips in scrubber sprayed with circulating water, and then to catalytic final cleaning. As a result, air is cleaned from hydrogen chloride to maximum allowable concentration and from nitrogen oxides to their residual content not exceeding 0.003 vol.%. EFFECT: provided prolonged efficient operation of cleaning equipment. 2 cl, 1 ex

Description

 The invention relates to hydrometallurgy of gold and can be used to extract gold from waste, recycled materials, electronic scrap by acid methods, in particular aqua regia.

 With the development of the electronic industry, the use of precious metals increases and, accordingly, the amount of waste containing them, in particular scrap, defective electronic devices, parts of dismantled military equipment, etc. increases, and enterprises for the processing of such raw materials are located directly in the area of electronic industry plants, that is, in the city.

 In this regard, the issue of neutralizing gas emissions from such enterprises is an acute issue, since when processing raw materials with aqua regia, an air-gas mixture containing hydrogen chloride and nitrogen oxides is formed.

 Known methods of gas purification are aimed at purifying air from oxides of sulfur, carbon, nitrogen, or mixtures thereof, however, with a simultaneous content of nitrogen oxides and hydrogen chloride, such a mixture is difficult to neutralize.

 Therefore, in the processes of acid dissolution of gold-containing materials, where a significant amount of gas is released, sprays, sublimates, and mists of solutions containing precious metals are formed, most often only metals are captured by passing the gas phase through a filter material - glass wool, which is then processed (Metallurgy of precious metals. Under Edited by L. V. Chugaev. M., Metallurgy, 1987, pp. 340-341). An air-gas mixture containing acidic components is dispersed in air.

 A known method of purification of exhaust gases generated during the etching of metals in baths with nitric acid from nitrogen oxides. A part of the gases is trapped in water, and air purification is carried out by mixing with water fog and passing through a sorbent - silica gel treated with urea (Auth. Sv. USSR 1824748, B 01 D 53/34, 1996).

 The disadvantages of this method are the preference for its use for the processing of gas mixtures highly oxidized by nitrogen oxides, the need for periodic complex operations of applying carbamide to silica gel, and the limited purification of gas-air mixtures at low temperatures.

 The closest analogue in technical essence and the achieved result is a method for extracting gold from gold-containing materials, including processing the starting materials with a solution containing hydrochloric acid to obtain a gold-containing solution and a gas-air mixture, which is passed through a scrubber irrigated with circulating water. Gold hydrochloride salts are periodically extracted from irrigation water. With this purification of the gas-air mixture, partial absorption of hydrogen chloride is achieved (Baymakov Yu. V., Zhurin A.I. Electrolysis in hydrometallurgy. M., Metallurgy, 1977, pp. 112-114).

 The disadvantages of this method are the incompleteness of purification of air from hydrogen chloride, the inability to use it for the effective purification of a gas-air mixture of complex composition.

 The technical result, which the applicant seeks to achieve in his invention, is to increase the degree and complexity of purification of exhaust gases when processing gold-containing materials with a mixture of hydrochloric and nitric acids (aqua regia).

To achieve this result in a method for extracting gold from gold-containing materials, including treating the starting material with a solution containing hydrochloric acid to obtain a gold-containing solution and a gas-air mixture, passing it through a scrubber irrigated with circulating water, according to the invention, the gas-air mixture is preliminarily passed through an alkaline solution, further transmission is conducted through a scrubber containing steel chips, at a speed of 0.1-0.5 m / s, irrigation with water is carried out at a density of irrigation 0.8-1 m ³ / (m ² • h), followed by catalytic treatment of the remaining gases. In this case, steel chips of fraction (3-4) • 1 • 0.25 mm are used.

 The essence of the method is as follows.

 When processing gold-containing materials with aqua regia, a gas mixture is formed containing oxide and nitrogen dioxide, hydrogen chloride, and gold-containing aerosols. Until recently, only gold was recovered from gas-air mixtures, as described above, and acid gases were discarded without treatment. Since the enterprises for processing secondary raw materials containing precious metals are located in populated areas, the problems of air pollution are becoming more acute.

 The complex composition of gases in ventilation emissions does not allow for deep purification by known methods, since the presence of hydrogen chloride even in low concentrations poisons the catalyst for neutralizing nitrogen oxides. Passing a gas-air mixture through an alkaline solution allows you to extract gold, absorb the bulk of hydrogen chloride, part of nitrogen oxides. However, purification of exhaust gases to MPC by HCl in this way is not possible due, in particular, to the difficulty of forming and uniform distribution in the volume of the alkaline solution of fine-sized gas-air bubbles of the same size sparged through the thickness of the bubble, the existence of heavily trapped fog with droplet-liquid HCl inside different sized bubbles. In the presence of HCl, effective catalytic purification of nitrogen oxides is not provided, the catalyst is poisoned, and its service life is significantly reduced.

To increase the efficiency of cleaning the gas-air mixture due to its complexity and completeness, the gas-air mixture that has undergone alkaline cleaning is subjected to passing through a scrubber filled with steel shavings at a speed of 0.1-0.5 m / s during irrigation of the scrubber with circulating water, which is conducted with intensity 0.8-1 m ³ / (m ² • hour).

 Hydrogen chloride, which is in the gas-air mixture after alkaline treatment, interacts with the base of steel chips - metallic iron, forming iron chlorides, which are washed off the surface of the chips with irrigation water. The transmission rate of the gas-air mixture, equal to 0.1-0.5 m / s, is due to the rate of interaction of hydrogen chloride with iron, which determines the completeness of purification of the gas-air mixture, as well as the volume of equipment required.

The high solubility of iron chloride in water contributes to the rapid renewal of the surface of the chips. The density of irrigation with water, equal to 0.8-1 m ³ / (m ² • hour), is sufficient to completely wash off the resulting iron chlorides. Increasing the flow of irrigation water leads to unproductive expenditure of energy on the circulation of the fluid.

The content of hydrogen chloride in the gas-air mixture passing through the scrubber is not more than 2 mg / m ³ , which is sufficient for the subsequent effective catalytic purification of air from nitrogen oxides.

Example
Scrap electronic devices - gold-containing contacts are subjected to tsar-vodka dissolution in pickling baths equipped with exhaust ventilation. In the process of dissolution, a gold-containing solution and a gas-air mixture (ventilation emissions) of the composition are formed, g / m ³ : 0.35 NO, 8.0 NO ₂ , 0.4 HCl, and also 18 vol.% O ₂ . Ventilation emissions of this composition are subjected to preliminary cleaning in a bubbler absorber filled with an alkaline solution. The air-gas mixture after this purification step contains in g / m ³ up to 0.2 NO, up to 2.0 NO ₂ and up to 0.05 hydrogen chloride. This mixture with a speed of 0.3 m / s is fed from below into a scrubber filled with steel chips fraction (3-4) • 1 • 0.25 mm.

 Shavings of this fraction are obtained by turning a steel blank with subsequent crushing, sieving and selection of a fraction (3-4) • 1 • 0.25 mm. The use of this fraction creates optimal hydraulic resistance to the gas-air flow, not exceeding 100 mm of water column.

The chips are irrigated continuously from above with water with an irrigation density of 0.9 m ³ / (m ² • h), the resulting solution circulates in the system for 2-3 years without replacement with its periodic replenishment with water.

The content of hydrogen chloride in the gas stream leaving the scrubber is 1.9 mg / m ³ .

 The neutralization of nitrogen oxides is achieved by their low-temperature selective catalytic reduction in the presence of ammonia, which provides a degree of purification from nitrogen oxides at the level of 98-97.5%.

 As a result, air containing hydrogen chloride impurities at the level of its maximum permissible concentration and nitrogen oxides in an amount not exceeding 0.003 vol.% Is released into the atmosphere.

 Thus, the proposed method allows for deep neutralization of toxic gases of complex composition with a low concentration contained in the vent emissions of acid baths of dissolving gold-containing materials, to increase the service life of the catalyst for the neutralization of nitrogen oxides from several days to a year, thereby reducing the consumption of precious metals (when using catalysts containing them), reduce the cost of the process of purification of the gas-air mixture, recover HCl to obtain a concentrated solution of chlorine iron, which provides the possibility of involving the latter in economic turnover, to reduce environmental pollution.

Claims (2)

1. A method of extracting gold from gold-containing materials, comprising treating the starting material with a solution containing hydrochloric acid to obtain a gold-containing solution and a gas-air mixture, passing it through a scrubber irrigated with circulating water, characterized in that the gas-air mixture is preliminarily passed through an alkaline solution, further passing led through the scrubber, comprising a steel shavings, at a rate of 0.1 - 0.5 m / s, irrigation water, irrigation is conducted at a density of 0.8 - 1 m ³ / m ² • h, with subsequent katalitiche Coy remaining cleaning gases.  2. The method according to claim 1, characterized in that the steel shavings are used in the form of a fraction (3 - 4) • 1 • 0.25 mm.