The Impact of Slime Content on Gold Leaching Process and Corresponding Strategie

In gold cyanide leaching processes, the presence of slime (typically referring to fine-grained minerals with particle sizes less than 37 or 74 micrometers) is a double-edged sword. A suitable amount of slime helps expose gold particles and increases the reaction surface area, but excessive slime content can bring a series of challenging problems to the entire leaching process.

Impact on the Leaching Chemical Environment

Due to its large specific surface area, slime exhibits strong adsorption characteristics. During cyanide leaching, slime adsorbs a large amount of cyanide ions and dissolved oxygen from the solution, leading to a decrease in the effective leaching agent concentration and an increase in sodium cyanide consumption. More seriously, clay minerals and organic carbon in the slime, which are known to "steal gold," preferentially adsorb dissolved gold-cyanide complexes, causing gold loss and reducing the leaching rate. Studies have shown that when the activated carbon content in the slime exceeds 0.05%, the gold adsorption loss rate can be as high as 15%-30%.

Limitations on Solid-Liquid Separation and Washing

High slime content significantly deteriorates the settling and filtration performance of the slurry. Fine-grained minerals form a stable colloidal system in the slurry, resulting in extremely slow settling. Excessive solids content in the thickener overflow not only causes metal loss but also increases the burden on subsequent precious metal solution purification. In the countercurrent washing (CCD) process, slime clogs the filter cloth, reduces filtration efficiency, and makes it difficult to achieve the washing rate target, resulting in a large amount of soluble gold remaining in the tailings.

Impact on Process Flow and Equipment

Increased slime content increases slurry viscosity, requiring increased agitation power and accelerating wear on equipment such as mixing tanks, pipes, and pumps. In the carbon-in-pulp (CIL/CIP) process, slime easily clogs the micropores of activated carbon, contaminates the carbon surface, reduces gold loading capacity and adsorption rate, and can even lead to a more than doubling of the carbon regeneration frequency.

Countermeasures

For ores with high slime content, the following measures can be taken: First, pre-desliming can be performed by separating some slime during the grinding and classification stage using equipment such as hydrocyclones, reducing its impact on subsequent processes; second, the reagent formulation can be optimized by adding dispersants (such as water glass) to improve the rheological properties of the slurry and reduce the disordered adsorption of slime; third, pre-oxidation treatment can be used to destroy the activity of gold-trapping substances on the surface of the slime; fourth, high-shear mixing equipment can be selected to enhance the mass transfer process.

In summary, controlling the slime content is a key aspect of gold ore leaching process management. Process parameters need to be rationally formulated based on the ore properties to find the optimal balance between leaching rate and processing cost.