How to Reduce Sodium Cyanide Consumption of Gold Cyanidation Plants?

At present, most gold processing plants use sodium cyanide as the gold extraction chemical. The gold cyanidation method is welcomed by many gold mine owners all over the world because of its simple process and high recovery rate. Before we have talked about how is sodium cyanide consumed during gold cyanidation process, this article will show you how to reduce the consumption of sodium cyanide.

1. Strengthen the Inflation and Improve the Oxygen Supply Quality

Increasing aeration and increasing oxygen supply can reduce unnecessary consumption of liquid cyanide. At present, most gold cyanidation plants use low pressure (0.2mpa) oil-free air compressor for air supply, and the air supply volume is between 0.5-1.0m3/min tank. In order to improve the quality of the air supply, you set a small hole hood at the end of the air supply pipe to generate a large number of small diameter bubbles, or install a check valve to prevent backwardation.

2. Strictly Control the Copper Grade of Raw Ore

Copper consumes a large proportion of cyanide in the leaching process. For example, a gold cyanidation plant has a copper grade of 0.548% in raw ore, and the mother liquor of the first leaching contains 1161mg/L copper, which consumes 37.6% of the annual cyanide consumption. Due to the high copper content of the dissolving solution, in order to maintain the gold leaching activity of the solution, the sodium cyanide concentration in the slurry must be increased accordingly, which further increases the consumption of sodium cyanide. Therefore, controlling the copper content of the raw ore can not only reduce the sodium cyanide consumed by dissolving copper, but also greatly reduce the sodium cyanide concentration in the leaching solution.

In order to reduce the grade of copper, you can pretreat it by flotation or other methods, and then leaching gold after copper is separated.

3. Control the Ratio of CN- and O2 Concentration in the Slurry

During the gold leaching process, air and sodium cyanide must be added to ensure the leaching of gold. The diffusion rate of gold in the solution depends not only on the concentration of CN– and O2 in the solution, but also on the concentration of CN– per unit gold surface, the concentration of dissolved O2, the surface area of gold particles and the thickness of the electric double layer.

CN–/O2=4x(Dissolved oxygen diffusion coefficient/sodium cyanide diffusion coefficient)
=4×(2.76×10-5cm/s ÷1.83×10-5cm/s)=4×1.5=6

This ratio is called the limit dissolved ion concentration value of dissolved gold.

For different types of ore, its value can be adjusted in the range of 4.6 to 7.4 to determine the best benefit ratio. If excessive sodium cyanide or air is added during the leaching process, it will not increase the leaching rate of gold and cause waste. Therefore, in the gold leaching process, it is often necessary to analyze and control the free cyanide and the oxygen content in the solution to keep the ratio of the two at about 6.

4. Establish the Dosage Balance of Cyanide

Sodium cyanide is the main consumption agent of gold cyanidation process. Therefore, the balance of sodium cyanide dosage should be frequently studied. The so-called cyanide balance refers to the balance between the cyanide discharged from the leaching solution and the actual consumption of sodium cyanide, which is related to the process technical indicators, economic costs, environmental treatment and other costs.

In addition to the formation of various complexes and compounds, the loss of sodium cyanide also includes the adsorption of clay sludge, the adsorption of mineral particles and the escape of a very small amount of hydrogen cyanide. The former consumption should account for about 90%. If it is lower than this value, it should be attributed to the quality of sodium cyanide, raw ore components, and water balance, or the measurement in operation, or “dropping, leaking, bubbling and leaking”.

5. Control Reasonable Calcium Oxide (CaO) Concentration

In the process of oxidative gold extraction, lime must be added.And it is very important to maintain a proper calcium oxide concentration. Its main functions are:

• CaO can increase the pH value of the leach solution, reduces the concentration of HCN produced and reduces the volatilization of HCN gas.
• Due to the addition of Ca2+ in the solution, the leaching rate of copper significantly decreased, preventing the formation of Fe (CNS) 4, and the concentration of CNS-ions in the solution decreased. Ca2+ prevents the combination of CN- with Cu and S, thus effectively reducing the consumption of cyanide.

After repeated trials, experts believe that it is reasonable to add calcium oxide 12 g/kg.

Wrap Up

The above are 5 ways to reduce the amount of sodium cyanide in gold cyanidation plants. In actual production, the amount of various elements can be appropriately adjusted according to the actual situation to reduce the consumption of sodium cyanide, save costs, and reduce the harm of cyanide wastewater to the environment.

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