RU1741473C - Method for deoxidizing gold-containing cyanide solutions - Google Patents

Abstract

FIELD: noble metal hydrometallurgy. SUBSTANCE: this method prescribes feeding solution containing 6.5 mg/l oxygen into electrolyzer cathode space isolated from anode space by ion-exchange membrane, maintaining cathode current density at 5.0 A/sq. m and current strength at 0.5 A, cathode space solution flow rate at 5,0 А/m² l/h. Deoxidizing degree is 96.1 %. Oxygen flow yield is 77.1 %. Used solution oxygen concentration: 0.25 mg/l. EFFECT: oxygen flow yield increased 35 to 40 times; intensified process.

Description

 The invention relates to hydrometallurgy of precious metals and can be used to deoxygenate gold-containing cyanide solutions before the deposition of precious metals by cementation.

 In cyanide solutions entering the precipitation of noble metals, a certain amount of dissolved oxygen is always present. Possessing a high oxidizing potential, oxygen is reduced during the cementation of precious metals by metallic zinc. As a result, a significant part of zinc metal is consumed uselessly during cementation, and the process itself is destabilized. Therefore, in practice, cyanide solutions are subjected to deoxygenation before precipitation of noble metals from them.

 A known method of deoxygenation of solutions (electrolytes) by electroreduction of dissolved oxygen at the cathode of the electrolyzer (electrochemical cell) in the process of passing a constant electric current through the solution circulating in the cell.

 The disadvantages of this method include the fact that the laws governing the rate of oxygen electroreduction are valid only for cells with a special electrode geometry with short-time switching and others in which the thickness of the oxygen diffusion layer near the electrode surface and electrolyte convection are constant. In this regard, the calculation of the rate of circulation of the electrolyte according to known patterns in industrial electrolyzers leads to errors that impede the implementation of the process. In addition, in the known method, along with electroreduction at the cathode of dissolved oxygen, oxygen is simultaneously released at the anode and, as a result, the solution is not oxygenated.

 Closest to the technical nature of the proposed is a method of deoxygenation of gold-containing cyanide solutions, including electrochemical reduction of oxygen in the cathode space of a membrane electrolyzer.

 In the known method, ion-exchange membranes prevent the oxygen released at the anode from penetrating into the cathode space. As a result, it is possible to deoxygenate the solutions by treating them in the cathode space of the membrane electrolyzer. The disadvantages also include the low efficiency of the process due to the low current efficiency of oxygen.

 The purpose of the invention is to increase the efficiency of the process by increasing the current efficiency of oxygen.

где V_p - скорость пропускания раствора, л/ч;
1,25 - коэффициент запаса;
l - сила тока на электролизере, А;
с - исходная концентрация кислорода в растворе, мг/л;
α = 300, электрохимический эквивалент кислорода, мг/А ˙ ч.This is achieved by the fact that in the method of deoxygenation of gold-containing cyanide solutions, mainly poor in gold content, including processing solutions in the cathode space of the membrane electrolyzer, the treatment is carried out at a cathode current density of 2-10 A / m ² and passing the initial solution at a speed determined by the formula
V _p = 1.25 ^-1

where V _p is the transmission rate of the solution, l / h;
1.25 - safety factor;
l is the current strength on the cell, A;
C is the initial concentration of oxygen in solution, mg / l;
α = 300, electrochemical equivalent of oxygen, mg / A ˙ h.

The method is as follows. An initial, for example, gold-containing cyanide solution with a gold concentration of 1-3 mg / l is fed through the cathode space of the membrane electrolyzer and at the same time a constant electric current is passed through the solution at a cathode current density of 2-10 A / m ² .

+2OH^- (2)
Выделяющийся в виде мелких пузырьков водород, длительное время удерживаясь в растворе, предотвращает насыщение его атмосферным кислородом.Under the influence of electric current in the solution being treated, the reaction of electrochemical reduction of oxygen
O ₂ + 2H ₂ O + 4e __ → 4OH ^- (1)
which provides deoxygenation of the solution, and then the water recovery reaction
2H ₂ O + 2e-H

+ 2OH ^- (2)
Hydrogen released in the form of small bubbles, being kept in solution for a long time, prevents its saturation with atmospheric oxygen.

+4H⁺ (3)
Однако насыщения обрабатываемого раствора выделяющимся кислородом не происходит, так как ионообменная мембрана препятствует проникновению кислорода в катодное пространство. Удельнообъемную скорость пропуска обрабатываемого раствора через катодное пространство регулируют в зависимости от силы тока на электролизере (катодной плотности тока) и исходной концентрации кислорода в растворе по формуле
V_p= 1,25^-1·I·

где 1,25 - коэффициент запаса;
l - сила тока на электролизере, А;
с - исходная концентрация кислорода в обрабатываемом растворе, мг/л;
α - электрохимический эквивалент кислорода, 300 мг/А˙ ч.At the same time, in the anode space of the electrolyzer in the anolyte, a 10% solution of sodium sulfate is the reaction of electrolytic decomposition of water with the release of gaseous oxygen
2H ₂ O-4e __ → O

+ 4H ⁺ (3)
However, saturation of the treated solution with released oxygen does not occur, since the ion-exchange membrane prevents the penetration of oxygen into the cathode space. The specific volumetric flow rate of the treated solution through the cathode space is regulated depending on the current strength on the electrolyzer (cathodic current density) and the initial oxygen concentration in the solution according to the formula
V _p = 1.25 ^-1

where 1.25 is the safety factor;
l is the current strength on the cell, A;
C is the initial concentration of oxygen in the treated solution, mg / l;
α is the electrochemical equivalent of oxygen, 300 mg / Ah.

The proposed method is tested in laboratory conditions for deoxygenation of poor gold-bearing cyanide solutions in a diaphragm electrolyzer with a working surface of cathodes of 10 dm ² .

 The cathode space of the electrolyzer in the form of six cathode chambers with cathode blocks made of a titanium sheet and having a highly developed surface is separated from the anode compartment located along the longitudinal walls of the cathode chambers by an MK-40L cation exchange membrane.

. Одновременно через обрабатываемый раствор пропускали постоянный электрический ток при напряжении 6 В и силе тока 0,1-1,1 А (при катодной плотности тока 1,0-11,0 А/м²).The treated solution with a volume of 1 dm ³ with an initial oxygen concentration of 6.5 mg / L was fed into the electrolyzer through a fitting in the lower part of the first cathode chamber, sequentially passed from one chamber to another in a sinusoid and was released from the electrolyzer through a fitting in the upper part of the last cathode chamber. The flow rate of the solution through the cathode space of the electrolyzer was regulated according to the formula V _p = 1.25 ^-1 · I ·

. At the same time, a constant electric current was passed through the treated solution at a voltage of 6 V and a current strength of 0.1-1.1 A (at a cathodic current density of 1.0-11.0 A / m ² ).

 After passing through the solution of 0.003 A · h of the amount of electricity, the oxygen concentration in the solution was less than 0.3 mg / L.

It was experimentally established that the implementation of the method is most effective when a constant electric current of a cathode density of 2-10 A / m ^{2 is} passed through the solution, since at the same time the solution passes through the cathode space of the membrane electrolyzer to achieve an oxygen current output of more than 80%.

The implementation of the method at a current density of less than 2 A / m ^{2 is} possible (the degree of deoxygenation is 95.4%, the current efficiency is 78.5%), but it is impractical, since the flow rate of the solution through the cathode space is halved.

At a current density of more than 10 A / m ² , a hydrogen evolution reaction is simultaneously taking place, as a result, the current efficiency decreases, and the oxygen concentration in the solution increases and gold and silver can be deposited on the cathode.

 The invention improves the efficiency of the process of deoxygenation of solutions.

Claims (1)

METHOD FOR DESCRIPTION OF GOLD-CONTAINING CYANIDE SOLUTIONS, mainly poor in gold content, including processing solutions in the cathode space of a membrane electrolyzer, characterized in that, in order to increase the efficiency of the process by increasing the current efficiency of oxygen, the treatment is carried out at a cathode current density of 2-10 l / m ² and the transmission of the initial solution at a speed determined by the formula
V _p = 1.25 ^-1

where V _p - the transmission rate of the solution, l / h;
1.25 - safety factor;
l is the current strength on the electrolyzer, A;
C is the initial concentration of oxygen in solution, mg / l;
α = 300, electrochemical equivalent of oxygen, mg / A · h.