Hot Selling Gold Electrowinning and Desorption Device

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The Basic Principle for Desorption

After the active carbon has adsorbed the gold in the cyanide solution, the gold on the surface of the gold-loaded carbon in the cyaniding system and the one in the cyanide solution have established a reversible balance condition. And when the gold-loaded carbon desorbs, the similar balance condition also happens on it. When CN ¯ or OH ¯ is added to the desorption system, because these anions are more likely to be adsorbed by active carbon, and then they will replace the adsorbed Au(CN)2¯ out, the reversible balance for gold adsorption is destroyed, and forwards to the direction against gold adsorption. That is desorption for gold. Its desorbing process is as follows:

Desorption Mechanism for Gold

It can be regarded that desorption gold from coals is essentially as far as possible to destroy the balance of the active carbon adsorption, making the process to go against the direction of the adsorption gold. Thus increasing cyanide concentration, temperature, pressure or adding organic solvent all can help desorbing gold from the activated carbon.

However, increasing the cyanide concentration, the alkalinity and adding organic solvent will boost the production cost while increasing the temperature and pressure is more economic and remarkable.

When the pressure is increased to 0.5 MPa, the temperature can be up to 150 °C and the gold desorption speed under this circumstance is faster several times than that under ordinary pressure.

The Basic Principle for Electrolysis

The liquid acquired from desorbing gold-loaded carbon contains gold undoubtedly, and the gold can be retrieved through electrolysis. Because no other new materials mix into the electrolytic solution, a pure gold deposit can be obtained, and this will facilitate the process in next step. So, this method is used by most gold mine.

The gold exists in desorption liquid as (CN) 2 ¯. During the electrolysis process, the cathode separate out gold, silver and a small amount of copper and so on, together with hydrogen due to the water reduction. The oxygen separated out from the anode carries out the ion oxidation with hydrogen and creates carbon dioxide and nitrogen.

Main chemical reaction as follows:

The cathode reaction:

The anode reaction:

The main solution reaction:

Experimental research shows that: under normal conditions, the major processes during the gold electrolysis depends on the speed of Au(CN)2¯ diffusing to the cathode surface. The gold deposition rate is controlled only by mass transfer process, and its electrolytic efficiency can be indicated with the following formula:

Log(CO/C1)=KmtS/2.3F

In formula: Km=P/δ- mass transfer coefficient; P-discharge particles (Au (CN) 2 ¯) diffusion coefficient; δ-the thickness of diffused layer; CO-the original concentration of gold; Ct-the gold concentration after electrolysis; T-electrolytic time; S-cathode surface area.

It can make the electrolyte conductive rate advance if the electrolyte temperature is raised, which makes the gold cyanide ions or discharge particle (CN) Au 2 ¯ diffuse faster and reduce the dissolution of oxygen in electrolyte and competitive current reaction. Therefore, with the electrolyte temperature rising, the gold deposition speeds up and its deposition efficiency is also improved.