RU2460814C1 - Method for gold extraction from cyanide solutions with dissolved mercury contained in them - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: method for gold extraction from cyanide solutions with dissolved mercury contained in them, gold-bearing ores formed during leaching, involves sorption of gold and mercury on activated carbon with enrichment of activated carbon with gold and mercury. Then, gold desorption is performed with alkali-cyanide solution under autoclave conditions, gold electrolysis from strippants so that cathode deposit is obtained and its remelting is performed so that finished products are obtained in the form of raw base gold alloy. Prior to gold desorption the selective desorption of mercury is performed by treatment of saturated carbon with alkali-cyanide solution containing 15-20 g/l of sodium cyanide and 3-5 g/l of sodium hydroxide, at temperature of 18-20°C and atmospheric pressure during 10 hours.

EFFECT: simplifying the method due to mercury desorption in a separate cycle prior to gold desorption; improving selectivity of gold extraction and creation of possibility of safer conditions during processing of cathode deposits so that finished products are obtained.

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Description

The invention relates to the field of sorption technology for the extraction of gold from solutions obtained as a result of cyanide leaching of gold ore products.

In some gold-bearing ores, accompanying metals are present, in particular mercury, which reacts with sodium cyanide when gold is leached. Minerals, both sulfide and oxidized, interact with sodium cyanide to form cyanide complexes

Hg (CN) ₂ ⁰ , Hg (CN) ₃ ^1- and Hg (CN) ₄ ^2-

In sorption processes using activated carbon to process gold-containing cyanide solutions in the presence of dissolved mercury and a concentration of free cyanide ion in the range of 0.5-1.0 g / l, sorption of low-charged mercury complexes: neutral Hg (CN) ₂ ⁰ and singly charged Hg predominates (CN) ₃ ^1- having a stronger affinity for activated carbon than the multiply charged anion Hg (CN) ₄ ^2- .

It is also known that the neutral mercury complex Hg (CN) ₂₀ ⁰ during sorption noticeably competes directly with the singly charged gold anion Au (CN) ₂ ^1– for adsorption sites on the surface of activated carbon and even displaces a certain amount of already adsorbed gold from the saturated carbon phase [ GJMcDougall, RDHancock, MGNicol. - "The mechanism of the adsorption of gold cyanide on activated carbon." - Joumal of the South African Institute of Mining and Metallurgy, September 1980, p. 354-355].

When the concentration of the free cyanide ion is more than 1 g / L in the solution, multiply charged complex anions Hg (CN) ₄ ^{2– are formed} , weakly sorbed by activated carbon and poorly retained in the sorbent phase.

The prototype of our method of sorption extraction of gold from cyanide productive solutions of leaching of gold ores in the presence of dissolved mercury can be a process that includes:

- production of activated carbon saturated with gold, which also contains mercury;

- joint desorption of gold and mercury with an alkaline cyanide solution in autoclave conditions (elevated temperature 130-150 ° C and pressure 4-5 atm) to obtain a marketable desorbate containing both gold and mercury;

- the joint release of gold and mercury in the cathode precipitate during the electrolysis of a solution of commodity desorbate. The content in the cathode deposit is up to 50% gold and 3-6% mercury;

- removal of mercury from the cathode deposit by distillation (distillation) in special retort furnaces before smelting crude gold;

- smelting of mercury-free cathode deposits with fluxes to produce finished products in the form of a draft alloy of alloyed gold without mercury.

In this case, gold and mercury are jointly extracted from cyanide solutions to activated carbon almost completely. Separation of mercury from gold is possible only at the stage of distillation of mercury from cathode deposits in retort furnaces. ["Introduction to Evolution Design and Operation of Precious Metal Heap Leaching Projects." - Mining Engineering Inc., Colorado, 1988; Mining magazine, November 1987, p. 404-403].

The disadvantages of this method of extracting gold are:

- multi-stage process;

- release of mercury together with gold in many operations, which are a source of aerosol formation of mercury and increased toxicity in industrial premises;

- the difficulty of removing mercury from the process;

- low process efficiency.

The task to which the proposed method is directed is to prevent mercury from entering the main gold recovery cycle from saturated activated carbon, i.e. gold desorption processes to produce mercury-free merchandise desorbate; electrolysis of gold from commodity desorbate with the formation of a cathode precipitate that does not contain mercury; exclusion from the process of the operation of distillation of mercury from the cathode deposit; melting cathode gold with fluxes to produce finished products in the form of a draft alloy of alloyed gold without mercury.

To solve it, it is necessary to create conditions that ensure the removal of mercury from saturated activated carbon before gold desorption.

The technical result of the invention is to simplify the method by conducting selective desorption of mercury in a separate cycle before desorption of gold, increasing the selectivity of gold extraction and creating safer conditions for the processing of cathode deposits to produce finished products.

The technical result is achieved by the fact that in the method for extracting gold from cyanide solutions with dissolved mercury present in them, which are formed during the leaching of gold-bearing ores, including sorption of gold and mercury onto activated carbon with saturation of activated carbon with gold and mercury, desorption of gold with an alkaline cyanide solution in autoclave conditions, the electrolysis of gold from desorbates to obtain a cathode deposit and its remelting to obtain finished products in the form of a draft alloy of ligature gold, pre about before desorption of gold in autoclaved conditions, selective desorption of mercury is carried out by treating saturated activated carbon with an alkaline cyanide solution containing 15-20 g / l NaCN and 3-5 g / l NaOH at a temperature of 18-20 ° C and atmospheric pressure for 10 hours.

The method is as follows.

Example:

1. The initial saturated activated carbon containing 5.6 mg / l of gold and 7.5 mg / l of mercury was treated with an alkaline cyanide solution in a laboratory autoclave at a temperature of 130 ° C. In the joint desorption of gold and mercury, a commodity desorbate was obtained containing 238 mg / l of gold and 367 mg / l of mercury. The electrolysis of the desorbate (current strength is 1A, voltage is 3.4 V, the anode is graphite, and the cathode is stainless steel) leads to the formation of a cathode deposit containing 51.5% gold and 11.6% mercury.

The resulting product requires additional operations to remove mercury before the smelting of the cathode deposit and obtaining ligature gold.

2. The initial saturated activated carbon containing 5.6 mg / g of gold and 7.5 mg / g of mercury with a volume of 50 ml was placed in a laboratory desorption column and in the mode of supply of a desorption solution containing 20 g / l NaCN + 5 g / l NaOH , in dynamic conditions at a speed of 1 vol./about. coal · hour at a temperature of 18-20 ° C experiments were conducted on selective desorption of mercury. The duration of the desorption process is 10 hours. After the end of the desorption experiment, a weighed portion of activated carbon was washed from the reagents with a four-fold volume of water, dried, and analyzed for the residual mercury content in activated carbon after desorption.

Solutions of selective desorption of mercury from saturated activated carbon with a content of 0.2 mg / l of gold and 200-300 mg / l of mercury enter the operation of purification from mercury by precipitation of an insoluble precipitate of mercury sulfide (PR _Hgs = 4.1 · 10 ^-54 ), separating the precipitate from the solution by filtration. Solutions cleared of mercury are strengthened with NaCN and NaOH and returned to the process of selective desorption of mercury.

The experimental results are given in table 1-4.

Table 1 Effect of NaCN concentration in a stripping solution on the extraction of mercury from activated carbon Alkali concentration - 5 g / l NaOH Temperature - 20 ° С Duration - 10 hours. The concentration of NaCN, g / l The residual mercury content in coal, mg / g Desorption of mercury during desorption,% 10 0.1 98.67 fifteen 0.003 99.96 twenty 0.001 99,99 thirty 0.002 99.97 40 0.005 99.93

The most effective concentration of NaCN in the stripping solution is 15-20 g / L. The extraction of mercury from activated carbon during desorption was ~ 100%. Increasing the concentration of NaCN more than 20 g / l is impractical.

table 2 Effect of NaOH concentration in a stripping solution on the extraction of mercury from activated carbon NaCN concentration - 20 g / l Temperature - 20 ° С Duration - 10 hours. The concentration of NaOH, g / l The residual mercury content in coal, mg / g Desorption of mercury during desorption,% 2 0.05 99.30 3 0.01 99.90 5 0.005 99.93

The data in Table 2 show that mercury extraction during desorption above 99.5% is achieved at an alkali concentration of 3-5 g / l NaOH.

Table 3 Temperature dependence of mercury recovery during desorption from activated carbon NaCN concentration - 20 g / l NaOH concentration - 5 g / l Duration - 10 hours. Desorption process temperature, ° С The residual mercury content in coal, mg / g Desorption of mercury during desorption,% fifteen 0.01 99.90 twenty 0.001 99,99 thirty 0.3 96.00

From the data given in Table 3, it follows that the maximum mercury recovery of ~ 100% was achieved at a temperature of 20 ° C. An increase in temperature to 30 ° C leads to a sharp decrease in the degree of extraction of mercury during desorption.

Table 4 Effect of desorption duration on mercury recovery from activated carbon NaCN concentration - 20 g / l NaOH concentration - 5 g / l Temperature - 20 ° С Duration of desorption, hour The residual mercury content in coal, mg / g Desorption of mercury during desorption,% four 0.5 93.30 6 0.2 97.30 8 0.006 99.92 10 0.001 99,99

The results shown in Table 4 indicate that, ceteris paribus, the maximum extraction of mercury from activated carbon ~ 100% is achieved with a desorption process of 10 hours.

Thus, it has been experimentally proven that the method for extracting gold from cyanide solutions with dissolved mercury present in them, when the selective desorption of mercury is performed prior to gold desorption, subject to the following parameters:

- temperature 18-20 ° C at atmospheric pressure;

- the concentration of NaCN is 15-20 g / l;

- concentration of NaOH - 3-5 g / l;

- the duration of the process is 10 hours, has several advantages:

1. Significantly increases the degree of selective gold recovery by eliminating mercury competition.

2. The process is greatly simplified by eliminating the complex and time-consuming operations of separating gold and mercury, since the latter is completely removed before gold desorption.

Claims (1)

A method for extracting gold from cyanide solutions with dissolved mercury present in them, formed during the leaching of gold-bearing ores, including sorption of gold and mercury on activated carbon with saturation of activated carbon with gold and mercury, desorption of gold with an alkaline cyanide solution in autoclave conditions, electrolysis of gold from desorbates with obtaining a cathode deposit and its melting to obtain the finished product in the form of a rough alloy of ligature gold, characterized in that before the desorption of ash and selectively carried out by treatment with mercury desorption saturated carbon alkaline cyanide solution containing 15-20 g / l of sodium cyanide and 5.3 g / l of sodium hydroxide at a temperature of 18-20 ° C and atmospheric pressure for 10 hours.