With the development of gold smelting technology, the development and utilization of low-grade gold mines has attracted more and more attention.Heap leaching gold extraction process has become an effective method for processing low-grade gold-containing oxidized ores.Because its investment and production costs are lower than that of the cyanide method, it is used to treat low-grade gold-containing oxidized ores, waste stone piles and discarded gold-containing tailings. There are significant economic benefits. The following is a detailed introduction to common problems and key technologies in the production of gold heap leaching.

1. Ore structure and its physical and chemical properties

In general, if the ore structure is loose and the cracks are developed, its permeability is better, which is conducive to the penetration and diffusion of cyanide solution into the ore, so that the gold is fully dissolved. Therefore, its leaching speed is faster.

If the ore contains carbonaceous materials, it will prevent the solution from entering the ore particles wrapped in it, thereby seriously hindering the dissolution of gold, and the active carbon can adsorb the dissolved gold, causing the gold to be lost with the tailings.

If the ore contains non-precious metal compounds such as copper, lead, zinc, arsenic, iron, etc., it also affects the dissolution of gold. If the precious liquid is replaced with zinc, the effect is poor and the consumption of cyanide will be increased.

In addition, if the concentration of sulfur ions in the cyanide solution reaches 5×10-7.It will reduce the dissolution rate of gold, and flotation agents such as flavonoids and dithiophosphates will also reduce the dissolution rate of gold.

2. Ore particle size

The size of the ore particle size has a great impact on the leaching rate. In general, the smaller the particle size, the shorter the leaching time required, and the higher the leaching rate.

However, in production practice, if the fine-grained content is too high (meaning that the content of -0.074mm exceeds 35% or more), it will affect the leaching rate (generally reduced by about 3 to 5%).This is because too much fine-grained particles will cause the surface of the ore pile to form grooves and affect the penetration of the solution.

3. Clay content in raw ore

The amount of clay content in the raw ore has a significant impact on leaching.Studies have proved that when the clay is wetted by a cyanide solution, its volume will expand.Its volume increase rate is 25 to 30%.This will lead to a decrease in the porosity of the ore pile and the penetration rate of the solution.

For ores with high clay content, the solution penetration rate varies with the change of leaching time. When the 10th d is leached, the solution penetration rate reaches 6L/t ore·D.Afterwards, due to the expansion of clay minerals, the porosity of the ore pile decreases, so the solution penetration rate is reduced to 3.5~4L/t ore·D.

4. Effect of PH value on leaching

pH value During the leaching process, the cyanide solution must maintain a certain alkalinity to prevent the decomposition of cyanide.Therefore, the pH value should be controlled between 9.5 and 11. If it is too high, the dissolution rate of gold will be reduced accordingly. When the pH value reaches more than 12, a thin film will form on the surface of the ore, which affects the dissolution rate of gold and prolongs the leaching time.

Lime is used as a protective base. When the pH is >11.5, it has a significant inhibitory effect on the dissolution of gold.This is due to the formation of a calcium peroxide film on the surface of the ore at high pH values to prevent it from reacting with cyanide.