Research on Pretreatment Technologies of Gold Concentrates before Cyanide Leaching

Cyanide leaching of Gold Concentrates is a classic process for gold extraction. However, due to the complex nature of the ores, Pretreatment is often required to improve the leaching efficiency. This article systematically combs through the pretreatment technologies before Cyanide Leaching, aiming to provide a reference for practical production.

I. Physical Pretreatment Technologies

1. Fine Grinding

The gold concentrates are ground to 325 mesh or finer through equipment such as ball mills to fully dissociate the gold minerals from the gangue. The practice in a certain gold mine shows that fine grinding can increase the exposure area of gold by 40%, and the leaching rate can be increased by 8-12%.

2. Screening and Impurity Removal

Equipment such as linear vibrating screens is used to remove impurities like wood chips and plastic fragments. The application case in a certain concentrator shows that after screening, the frequency of equipment blockage is reduced by 70%, and the adsorption loss of cyanide is reduced by 5%.

3. Flotation Reagent Removal

For flotation concentrates, a two-stage process of "regrinding - reagent removal" is adopted to effectively remove flotation reagents such as xanthate and No. 2 oil. Industrial data shows that after reagent removal, the consumption of Sodium Cyanide is reduced by 35%, and the adsorption rate of activated carbon is increased by 15%.

II. Chemical Pretreatment Technologies

1. Alkaline Pretreatment

Lime is added to adjust the pH to 10-11. so that harmful elements such as zinc, arsenic, and antimony form soluble salts. After its application in a certain arsenic-containing gold mine, the consumption of cyanide is reduced from 12 kg/t to 6.5 kg/t, and the leaching rate is increased by 9%.

2. Oxidation Pretreatment

• Air Oxidation

By aerating and stirring to oxidize the reducing substances, in a certain pyrrhotite-type gold mine, after pretreatment, the pulp potential is increased from -150 mV to +200 mV, and the cyanidation time is shortened by 40%.

• Addition of Oxidants

When the dosage of lead nitrate is 0.5 kg/t, the concentration of sulfide ions can be reduced by 60%, and the leaching rate is increased by 7%. In a certain copper-gold ore, the consumption of sodium cyanide is reduced by 40% after pretreatment with hydrogen peroxide.

3. Synergistic Leaching with Ammonia-Cyanide

Ammonia water (with a concentration of 1-3%) is added to the copper-containing gold concentrates to form stable ammonia complexes of copper. Industrial tests show that the copper leaching rate can be controlled below 5%, and the gold leaching rate is increased by 12%.

III. Biological Pretreatment Technologies

Microorganisms such as Thiobacillus ferrooxidans are used to decompose sulfide minerals. After 20 days of biological oxidation in a certain refractory gold mine, the decomposition rate of pyrite reaches 92%, and the gold leaching rate is increased from 35% to 88%. This technology has the advantage of environmental friendliness, but the treatment period is relatively long (15-30 days).

IV. Suggestions for Process Selection

The pretreatment process needs to be comprehensively selected according to the nature of the ore:

• For ores with high sulfur and high arsenic content, biological oxidation or roasting pretreatment should be preferentially adopted.

• For copper-containing gold concentrates, the ammonia-cyanide system is recommended.

• For flotation concentrates, reagent removal treatment needs to be strengthened.

• For conventional ores, a combined process of alkaline leaching and oxidant addition can be adopted.

Conclusion:

The rational application of pretreatment technologies can significantly improve the cyanide leaching effect. In the future, it is necessary to further study efficient and low-consumption combined pretreatment processes to promote the green development of gold extraction technologies.