RU2753352C1 - Method for recovering gold from solution containing impurities of platinum and base metals - Google Patents

Abstract

FIELD: precious metals hydrometallurgy.

SUBSTANCE: invention relates to the hydrometallurgy of precious metals, and in particular to a method for recovering gold from a solution containing impurities of platinum and base metals, and can be used to obtain gold in the form of a metal. The aforementioned gold-containing solution is treated with sodium hydroxide, sodium phosphate is introduced into the pulp and the impurity precipitate is separated by filtration. The filtrate is treated with a solution containing nitrite and sodium hydroxide in a molar ratio of NaNO₂ : NaOH=1:(1,4-2,1).

EFFECT: invention allows reducing the consumption of sodium nitrite, the release of nitrogen oxides into the gas phase and the content of nitrate ions in solutions after gold reduction, while the quality of gold corresponds to GOST 25058-89.

1 cl, 1 tbl, 1 ex

Description

The method relates to the hydrometallurgy of precious metals and can be used to obtain gold in the form of a metal.

There is a known method of recovering gold from a solution, including repeated evaporation of it in the presence of sodium chloride to remove most of the acid, treatment with sodium nitrite until there is no gas evolution, neutralization with sodium carbonate to a pH of about 8.5, separation of the precipitate and washing it in nitric acid (Beamish F.E. Analytical chemistry of noble metals. - Moscow: Mir, 1969. - vol. 2; p. 85).

The disadvantages are the duration of the evaporation process, the abundant release of nitrogen oxides into the gas phase, and the purity of the gold obtained is less than 99.99%.

There is a known method of separating gold from a chloride solution containing impurities of platinum and base metals, including processing the chloride solution with sodium hydroxide to pH 4.0-5.5, introducing sodium phosphate into the pulp in an amount of 15-20 kg / m3 solution, separating the sediment impurities, treating the filtrate with sodium nitrite until the redox potential in the solution reaches 450-550 mV relative to the silver chloride reference electrode, separating the gold precipitate and washing it in hydrochloric acid (Mamonov S.N., Ilyashevich V.D., Zolotoe A.F., Mikhnev A.D. ., RF Patent No. 2069498).

The disadvantage is the high consumption of sodium nitrite, the abundant release of nitrogen oxides into the gas phase, the formation of solutions containing a significant amount of nitrate ions.

This method is the closest in technical essence to the claimed one and is adopted as a prototype.

The technical result to be achieved by the alleged invention is the elimination of these disadvantages.

The specified technical result is achieved by the fact that in the known method for the recovery of gold from a solution containing impurities of platinum and base metals, including processing the solution with sodium hydroxide, introducing sodium phosphate into the pulp, separating the precipitate of impurities, treating the filtrate with sodium nitrite, separating the gold precipitate and washing it in acid - the filtrate is treated with a solution containing nitrite and sodium hydroxide in a molar ratio of NaNO ₂ : NaOH = 1: (1.4-2.1).

The essence of the method is as follows.

In the process of gold reduction with sodium nitrite, the following chemical reactions occur:

In this case, 2.1 kg of sodium nitrite is required to obtain 1 kg of gold, and 0.7 kg of NO ₂ in the gas phase and 1.3 kg of NaNO ₃ in solutions after reduction are formed.

According to the proposed method, the recovery of gold is carried out with a solution containing nitrite and sodium hydroxide according to reaction (3), according to which the consumption of sodium nitrite is reduced by 4 times and is 0.525 kg per 1 kg of gold, there is no gas evolution, and the content of NaNO ₃ in solutions after reduction decreases in 2 times up to 0.647 kg.

It has been experimentally established that the optimal molar ratio of nitrite and sodium hydroxide in a reducing agent solution, which reduces the consumption of sodium nitrite, the release of nitrogen oxides into the gas phase and the content of nitrate ions in solutions after reduction is NaNO ₂ : NaOH = 1: (1.4-2.1) ...

When the molar ratio of nitrite and sodium hydroxide in a solution is less than NaNO ₂ : NaOH = 1: 1.4, an increase in the consumption of sodium nitrite, the release of nitrogen oxides into the gas phase, and an increase in the content of nitrate ions in solutions after reduction are observed. When the molar ratio of nitrite and sodium hydroxide in the solution is more than NaNO ₂ : NaOH = 1: 2.1, the quality of the finished product decreases and an increase in the gold content in the solutions after reduction is observed.

Below is an example of the implementation of the method.

Example

5 L of a chloride solution with a concentration of gold 200 g / L, silver 150 mg / L, copper 15 g / L, palladium 1.2 g / L was poured into the reactor, sodium hydroxide solution was added until pH = 4.5 in the pulp, then 90 g was introduced into the pulp sodium phosphate and kept for 0.5 hour. The pulp was filtered off, the filtrate was divided into 5 parts. The first part of the filtrate was treated with a sodium nitrite solution (according to the prototype method) until the redox potential in the solution was 500 mV relative to the silver chloride reference electrode. The rest of the filtrate was treated with a solution containing nitrite and sodium hydroxide in different molar ratios (according to the claimed method) until the value of the redox potential in the solution is 500 mV relative to the silver chloride reference electrode. During processing, gas evolution was determined visually. Gold precipitates from each portion of the solution were separately filtered, washed sequentially with hydrochloric acid, and then with water, and analyzed for the content of impurities in accordance with GOST 25058-89 "Gold in powder". The solutions after gold reduction were analyzed for the content of gold and nitrate ions. The results of the experiments are shown in table 1.

As shown in the table below, the use of the proposed method can significantly reduce the consumption of sodium nitrite, the release of nitrogen oxides into the gas phase and the concentration of nitrate ions in solutions after gold reduction, while the gold quality is 99.99% and complies with GOST 25058-89.

Claims (1)

A method for recovering gold from a solution containing impurities of platinum and base metals, including processing the solution with sodium hydroxide, introducing sodium phosphate into the resulting pulp, separating the precipitate by filtration, processing the filtrate, separating the gold precipitate and washing it in acid, characterized in that the filtrate is processed a solution containing nitrite and sodium hydroxide in a molar ratio of NaNO ₂ : NaOH = 1: (1.4-2.1).