Skarn-type gold deposits are surface oxide ores and are heavily weathered. The ore contains a certain amount of copper oxide, the ore is acidic, and a large amount of alkali and sodium cyanide are consumed during cyanidation. The leaching process of low pH value and low concentration NaCN solution was adopted on site. This not only reduces the consumption of NaCN and alkali, but also improves the adsorption rate of activated carbon and the economic index of gold recovery.
Since skarn-type gold ore contains copper oxide and is acidic, the consumption of alkali and NaCN is very high if the general process conditions are used. Therefore, it is advisable to use a low-concentration NaCN solution for leaching at a lower pH value, so a column leaching test was performed under this condition.
Test conditions: The -60mm ore sample was first treated with 6kg/t lime to increase the pH of the pulp to 8.5, and then leached with 0.05%~0.02% NaCN solution. After 9 days leaching, the NaOH consumption was 647g/t , NaCN consumption was 556g/t. When the raw ore grade was 2.97g/t, the tailings grade was 0.25g/t, and the gold leaching rate reached 91.58%.
The results of the column leaching test show that the use of low-concentration NaCN solution leaching can not only significantly reduce the consumption of chemicals, but also improve the leaching rate.
The permanent yard heap leaching method is adopted. The raw ore is directly put into the pile without being crushed. The particle size of the ore is less than 300mm and the pile height is 4m.
After the leaching is completed, continue to build piles on the tailings for leaching. A total of three layers of ore are piled up.
The pH of the leaching solution is 9, the concentration of NaCN is 0.05%~0.02%, the leaching time is 80~120d. The highest grade of gold in the pregnant solution is 1.73mg/L, generally it is 0.4-0.8mg/L. And the grade of gold in the adsorption tailing solution is 0.01~ 0.1 mg/L. The highest grade of gold in gold-loaded carbon is 16.79kg/t, and generally it is about 12kg/t.
The capacity of the mine is 30,000t of ore annually, the average raw ore grade is 1.37g/t, the leaching rate is 73.7%, the lime consumption is 10.7kg/t, the NaOH consumption is 1.34kg/t, the NaCN consumption is 479g/t, and the power consumption is 1.76kW·h/ t.
The pH of the solution discharged from the ore heap is between 7 and 8, the low pH is beneficial to activated carbon adsorption. Therefore, the adsorption rate of activated carbon increases, and the grade of gold-loaded carbon also increases. Moreover, the low-grade adsorption tailings are beneficial to the leaching and washing of the ore heap.
