Cyanide leaching is one of the main methods for extracting gold from gold ore. For the treatment of gold-containing ores by cyanide leaching, the recovery rate of cyanide leaching mainly depends on the effect of the leaching operation. How to adopt reasonable leaching technology and equipment and how to choose reasonable leaching conditions while maintaining the overall cost of the concentrator and improving the technical and economic benefits of the concentrator need to be determined by gold leaching tests. The test items selected for the gold leaching test are roughly the same as those affecting gold leaching. Let us introduce ten tests for gold leaching below.

1. Grinding Fineness Test

The dissociation of gold monomers or the exposure of the gold surface is a necessary condition for cyanide leaching or new non-toxic leaching. Therefore, appropriately increasing the grinding fineness can increase the leaching rate. However, over-grinding increases the grinding cost and the possibility of leachable impurities entering the leaching solution, resulting in the loss of cyanide or gold leaching agent and dissolved gold. A grinding fineness test must be carried out first to select the appropriate grinding fineness.

ball mill

2. Pretreatment Agent Selection Test

Gold ore leaching requires a pretreatment agent selection test. It is usually necessary to compare the commonly used calcium peroxide, sodium hypochlorite, sodium peroxide, hydrogen peroxide, citric acid, lead nitrate, and other pretreatment agents with the normal situation without pretreatment agents. The purpose is to determine whether pretreatment operations are required.

Calcium peroxide, sodium hypochlorite, and sodium peroxide are very stable and widely used multifunctional inorganic peroxides and have the characteristics of long-term oxygen release. They can slowly release oxygen in the leaching slurry for a long time, which is conducive to improving the leaching rate of gold.

Hydrogen peroxide and citric acid provide sufficient oxygen during the leaching process and are the main reagents for generating oxygen. Lead ions (appropriate amount) of lead nitrate can destroy the passivation film of gold during the cyanide leaching process, accelerate the dissolution rate of gold, reduce the cyanide time, and increase the leaching rate of gold.

3. Amount of Protective Alkali Lime Test

To protect the stability of sodium cyanide solution or non-toxic gold leaching agent and reduce the chemical loss of gold leaching agent, an appropriate amount of alkali must be added during leaching to maintain a certain alkalinity of the ore pulp. Within a certain range of alkalinity, as the alkali concentration increases, the gold leaching rate remains unchanged, and the amount of gold leaching agent decreases accordingly. If the alkalinity is too high, the dissolution and leaching rate of gold will decrease instead. Therefore, it is necessary to determine the appropriate amount of protective alkali and the pH value of the ore pulp. Lime with a wide source and low price is usually used as the leaching protective alkali in experiments and production. To determine its specific usage and guide actual production.

4. Amount of Gold-leaching Agent Test

In the gold leaching process, the amount of gold leaching agent and the gold leaching rate are proportional within a certain range, but when the amount of gold leaching agent is too high, it not only increases the production cost but also the gold leaching rate does not change much. Therefore, based on the grinding fineness test, to further reduce the amount of gold leaching agent and production reagent cost, a gold leaching agent dosage test was carried out to determine the appropriate dosage.

5. Leaching Time Test

To achieve a high leaching rate during the leaching process, the leaching time can be extended to allow the gold particles to fully dissolve to increase the gold leaching rate. As the leaching time increases, the gold leaching rate gradually increases and finally reaches a stable value. However, if the leaching time is too long, other impurities in the slurry will continue to dissolve and accumulate, hindering the dissolution of gold. To determine the appropriate leaching time, a leaching time test is conducted.

Leaching Time Test

6. Slurry Concentration Test

During leaching, the slurry concentration will directly affect the leaching rate and speed of gold. The higher the concentration, the greater the viscosity of the slurry, the poorer the fluidity, and the lower the leaching rate and rate of gold. When the slurry concentration is too low, although the leaching rate and rate of gold are high, the equipment volume and equipment investment will increase, and the amount of leaching agents and other reagents will increase proportionally, which will increase the production cost accordingly. In order to determine the appropriate leaching slurry concentration, a leaching slurry concentration test is carried out.

7. Activated Carbon Pretreatment Test

For carbon leaching, hard and wear-resistant activated carbon must be used to prevent fine carbon from entering the leaching residue due to wear during the stirring and leaching process, causing gold loss and reducing the gold recovery rate. The test generally uses coconut shell activated carbon with a particle size range of 6 to 40 meshes. The activated carbon pretreatment conditions are water: carbon = 5:1, stirring for 4 hours, and stirring speed 1700 rpm. The activated carbon after stirring for 4 hours is sieved with 6-mesh and 16-mesh sieves. Remove the fine carbon under the sieve. That is, activated carbon with a particle size of 6 to 16 mesh is selected for carbon leaching and carbon adsorption tests.

8. Bottom Carbon Density Test

In the gold ore leaching test, it is generally determined to use coconut shell activated carbon with a particle size of 6-16 mesh to adsorb and recover the dissolved gold leached. After producing gold-loaded carbon, mature activated carbon is used for analysis and electrolysis of finished gold. The density of the bottom carbon directly affects the carbon adsorption rate. In order to select the appropriate bottom carbon density, a bottom carbon density test will be carried out.

gold leaching

9. Carbon Adsorption Time Test

In order to determine the appropriate carbon leaching (carbon adsorption) time and reduce the wear of gold-carrying carbon, after determining the total leaching time, it is necessary to conduct pre-leaching and carbon leaching (carbon adsorption) time tests.

10. Carbon Leaching Process Comprehensive Condition Parallel Test

In order to verify the stability of the carbon leaching test and the repeatability of test results, it is necessary to conduct a comprehensive condition parallel test of the whole process of carbon leaching test, that is, after determining the above 9 detailed condition tests, it is necessary to conduct a comprehensive verification test of the best conditions for each condition test.