Project Background
The deposit belongs to the medium and low-temperature hydrothermal gold deposit. Gold in the ore exists in the form of fine-grained inclusions in pyrite and arsenopyrite, and the traditional cyanide leaching rate is less than 70%. The customer is facing the following challenges:
- The gold recovery rate is low and there is serious waste of resources.
- Sulfides consume a large amount of sodium cyanide, and the cost of the chemical agent is high.
- Copper-containing impurities interfere with the leaching process, resulting in poor solution stability.
Techincal Solution
Regarding the characteristics of the ore, Henan Bailin Machinery has designed the “Pre-oxidation -CIL combined Process”. The core process is as follows:
01. Crushing and Grinding
- Raw ore is crushed to -25mm after two-stage closed circuit crushing process. The crushed ore is ground by ball mills to fineness of -0.074mm which is accounting for 85% after classification. It ensure the full dissociation of gold minerals.
02. Pre-oxidation treatment
- Add lime (pH=10.5) to adjust the alkaline environment of the pulp and inhibit the consumption of cyanide.
- Hydrogen peroxide (500g/t) was introduced as the oxidant to destroy the crystal structure of the sulfide and release the gold coating. The pre-oxidation time was 4 hours.
03. CIL Leaching and Adsorption
- Leaching conditions: 6-stage series leaching tank, sodium cyanide concentration 0.05%, activated carbon density 15g/L, leaching time 48 hours.
- Carbon management: Use high-quality coconut shell activated carbon (iodine value≥1000mg/g), and carbon countercurrent adsorption is carried out every 8 hours to ensure efficient loading of gold.
- Solution purification: Copper ions are removed by lead salt precipitation to maintain the copper content in the leachate below 50mg/L.
04. Desorption and electrolysis of gold-loaded carbon
- After the gold-loaded carbon is acid-pickled (5% HCl) to remove surface impurities, it enters the high-temperature and high-pressure desorption column (temperature 95℃, pressure 0.3MPa).
- The desorption liquid is used to recover gold by electrodeposition, with a current density of 300A/m², and the grade of the produced gold sludge reaches 92%.
Effect
- The recovery rate has significantly increased: The gold leaching rate has risen from 68% in the traditional process to 93.2%, and the total recovery rate has reached 91.5%.
- Cost optimization: The consumption of sodium cyanide per unit is reduced by 22%, and the cost of chemicals per ton of ore is decreased by 18%.
- Environmental benefits: Through solution recycling and copper ion recovery, the discharge of waste liquid is reduced by 30%.
