Although the applicability of heap leaching for gold extraction is not as good as that of flotation and cyanidation, many small-scale concentrators still use heap leaching when processing low-grade gold ores. If the effect of heap leaching for gold extraction is not satisfactory, then you should look for the reasons from the following five factors:
The influence of leaching solution on the effect of heap leaching is not small, which is mainly reflected in pH value, fluidity and oxygen content.
(1) pH value of leaching solution
The stability of pH value of leaching solution is crucial to the leaching process, because the change of pH value will affect the reaction activity of gold and cyanide. Among them, NaCN concentration is the key. If the NaCN concentration is too high, it will lead to an uncoordinated ratio of NaCN and oxygen, causing partial hydrolysis of NaCN, resulting in an increase in the pH value of the spray liquid, which in turn affects the leaching rate of gold.
(2) Fluidity of leaching solution
The porosity of the ore and the fluidity of the leaching solution directly affect the effect of heap leaching. High porosity and good permeability can accelerate the leaching rate of cyanide solution and improve the recovery rate of gold.
(3) Oxygen content of leaching solution
Oxygen plays an extremely important role in the leaching process. The use of oxidants is an important technical measure to improve the heap leaching of gold ore. For example, peroxides of barium, strontium and calcium can release oxygen into the solution, thereby promoting the leaching of gold.
(1) Occurrence state of gold in ore
The occurrence state of gold, such as the proportion of intergranular gold, encapsulated gold and fissure gold, will affect the heap leaching effect.
(2) Oxidation degree of ore
When the oxidation degree of ore is high, gold minerals exist in the form of natural gold, which is more suitable for heap leaching. For example, the gold particles of a certain gold mine are fine and the oxidation degree of the ore is high. It is not suitable to use gravity separation, but heap leaching is more suitable.
(3) Ore permeability
Ores with loose structure have better permeability, which is conducive to the penetration and diffusion of leaching solution, so that gold and leaching solution are fully in contact, accelerating the dissolution of gold. On the contrary, ores with dense structures or high clay content will hinder the contact reaction between the leaching solution and gold, resulting in low leaching rate.
(4) Influence of associated minerals
If the gold ore contains other associated minerals that consume cyanide and oxygen, the leaching rate of gold will be reduced. For example, the total amount of sulfides does not exceed 1%, and there is a trace amount of natural gold. The presence of these sulfides may affect the heap leaching effect.
Spraying and dripping are two different liquid distribution methods in the heap leaching process. Uniform liquid distribution is one of the key factors to improve the gold leaching rate. Drip technology is suitable for heap leaching production under natural conditions of drought, high temperature, strong wind and lack of water. Drip equipment investment is less than spraying, the solution evaporation is low, the peak period of gold leaching is advanced, the leaching time is shortened, and the leaching rate is improved.
In the heap leaching process of gold, the choice of spraying method determines the uniformity and efficiency of the contact between the leaching solution and the ore. Common spraying methods include dripping, spraying and circulating spraying. The appropriate spraying method can ensure that the leaching solution evenly penetrates the entire ore pile and improves the leaching rate of gold. In addition, factors such as spray intensity, spray time, and spray particle size will directly affect the coverage of the reagent and the reaction speed of the ore. Therefore, continuous optimization of the spray process can effectively improve the overall effect and economic benefits of the cyanidation process.
The impact of climate factors on the heap leaching effect is mainly reflected in temperature and weather. Temperature has a significant effect on the rate and effect of cyanidation reaction. Higher temperature can accelerate the dissolution of gold and increase the leaching rate of gold, but the temperature should not be too high, otherwise side reactions will occur and affect the recovery rate of gold. Meteorological factors such as precipitation, humidity, and wind speed will affect the heap leaching process. Higher humidity and more precipitation will lead to an increase in the moisture content of the heap leaching ore body, affecting the concentration and permeability of the leaching solution. Wind speed mainly affects the supply of oxygen. Therefore, reasonable control of environmental conditions is crucial to improving the recovery rate of heap leaching gold.
The effect of heap leaching gold extraction is mainly affected by the above five aspects. In actual production, we should focus on the operation of these five aspects. Once problems are found, they need to be adjusted in time to ensure the smooth leaching of gold and the final gold recovery rate.
