Cyanide Gold Preparation

With the depletion of high-grade gold ore reserves, studying low to medium grade and difficult to treat gold ore and strengthening traditional gold ore beneficiation processes have become the mainstream trend in global gold selection. Gold mines have high mining value, and their beneficiation process is relatively complex, with different beneficiation methods. At present, common gold ore beneficiation processes mainly include cyanide method, flotation method, and gravity separation method.

Cyanidation is one of the main methods for gold ore beneficiation. Usually, cyanide methods can be divided into two categories: agitation cyanide and filtration cyanide. Stirring cyanide is mainly used for processing flotation gold concentrate or full mud cyanide; And cyanide infiltration mainly deals with low-grade gold containing oxidized ores.

Gold extraction process using stirring cyanide method

The stirring cyanide method for gold extraction mainly includes two types of gold extraction processes. One is the so-called cyanide zinc replacement process, which involves continuous countercurrent washing and the use of zinc powder (wire) to replace precipitation and recover gold; Another type is the unfiltered cyanide slurry process, which uses activated carbon to directly adsorb and recover gold from cyanide slurry without the need for filtration and washing.

1. Cyanide zinc replacement process

The cyanide zinc replacement process is used for the treatment of gold containing precious liquids after cyanide leaching. The principle is to use zinc powder (wire) as a reducing agent to replace gold and silver from the leaching solution, mainly including countercurrent washing solid-liquid separation, leaching solution purification, deoxidation, and zinc powder (wire) replacement operations.

Countercurrent washing solid-liquid separation: Separate the cyanide precious liquid (leachate) from the solid.

Leaching solution purification: Remove suspended solids from the precious liquid (leaching solution), so that the gold containing precious liquid entering the replacement operation reaches a clear and transparent state.

Deoxygenation: Removing dissolved oxygen from precious liquids (leachate).

Zinc powder (wire) replacement: Use zinc powder (wire) to replace the precious metals in the precious liquid (leaching solution), forming gold (silver) mud.

2. Carbon slurry gold extraction process

The charcoal slurry method for gold extraction is to put activated carbon into cyanide slurry, adsorb the dissolved gold onto the activated carbon, and then extract gold from the activated carbon. This mainly includes the preparation of leaching raw materials, stirring leaching and countercurrent carbon adsorption, desorption of gold loaded carbon, electrowinning electrolysis, smelting ingots, carbon regeneration, and other operations.

Preparation of Leaching Raw Materials

When using the carbon leaching method for gold extraction, the preparation of the leaching raw materials includes physical crushing and grinding classification. Usually, the fineness of the grinding and grading overflow in the coal leaching gold extraction process is around -200 mesh, accounting for 85-95%.

Chip removal operation

The sawdust and debris in the slurry can easily cause blockages in pipelines and screens, as well as adsorb gold from the slurry and mix it into the rich carbon. Therefore, before leaching, it must be removed. If necessary, it is necessary to concentrate the slurry and add descaling agents, which can also reduce scaling on the surface of activated carbon and sieve. Generally, two chip removal operations are required in the grinding process, one at the overflow point of the first and second stage grinding classification. Chip removal equipment often uses medium frequency linear vibrating screens. In the first chip removal operation, spiral screens and cylindrical screens can also be used. The mesh size of the chip removal screen should be as small as possible while ensuring that the screen surface does not run.

Pre immersion concentration operation

When the overflow concentration of grinding and grading is mostly 18-22%, direct leaching is not suitable and pulp thickening must be carried out. It is recommended to use a high-efficiency thickener with a small footprint and high concentration efficiency.

Stirring leaching and countercurrent carbon adsorption

Leaching and adsorption are two independent operations. In the adsorption operation, the leaching process has been basically completed, and the size, quantity, and operating conditions of the adsorption tanks are determined by the adsorption parameters. Generally speaking, leaching operations require longer time than adsorption operations, so the size, inflation, and dosing of the tank are determined by leaching parameters. Due to the fact that adsorption rate is a function of the concentration of dissolved gold in the solution, in order to increase the concentration of dissolved gold in the front adsorption tank and increase the leaching time, it is usually necessary to add 1-2 stages of pre leaching before simultaneous leaching and absorption.

Gold loaded carbon desorption and electrowinning electrolysis

The gold carrying carbon and slurry are lifted to the carbon separation screen (usually a linear vibrating screen) through a carbon extraction pump or air elevator. The screen is washed with clean water to separate the carbon and slurry. The gold carrying carbon enters the carbon storage tank, and the slurry and flushing water enter the first adsorption tank. At present, the commonly used desorption method for gold loaded carbon is the high-temperature and high-pressure desorption method, which involves adding anions that are easily adsorbed by activated carbon in the desorption system to replace Au (CN) 2- and achieve the desorption of gold; The precious liquid obtained from desorption of gold loaded carbon is recovered by ionization method to obtain solid gold.

Smelting ingots

After acid washing and impurity removal, the obtained gold mud can be directly smelted into gold ingots. By using wet metallurgy, the purity of gold ingots can reach over 99.99%.

Carbon regeneration

After adsorption and desorption, activated carbon needs to be regenerated to restore its good adsorption performance. Generally, the activated carbon after desorption is first washed with acid to remove carbonate and other accumulated substances. After several cycles of return to use, it needs to undergo thermal activation to restore the adsorption activity of the carbon, and then it can be recycled. The main equipment includes activated carbon regeneration kiln, water quenching tank, fine carbon separation screen, etc.

3. Gold extraction process using cyanide ion exchange resin adsorption method

The process flow of ion exchange resin adsorption is basically similar to that of carbon slurry leaching and adsorption, with the difference being that carbon is replaced with ion exchange resin, which includes operations such as gold loaded resin electrolysis, ingot smelting, resin regeneration, etc.

Analysis and electrolysis of gold loaded resin

The gold resin and slurry are pumped or air lifted to the resin separation screen (usually a linear vibrating screen), and washed with clean water on the screen to completely separate the resin and slurry. The gold resin enters the resin storage tank, and the slurry and flushing water enter the first adsorption tank.

Feed the cleaned gold loaded resin into the analysis column, add the analysis solution, and perform a 36 hour cycle operation at a temperature of 40-60 ° C. The analyzed precious solution enters the electrolytic cell and is recovered by ionization to obtain gold mud.

Smelting ingots

After acid washing and impurity removal, the obtained gold mud can be directly smelted into gold ingots. By using wet metallurgy, the purity of gold ingots can reach over 99.99%.

Resin regeneration

The resin after analysis needs to be regenerated to restore its good adsorption performance. Add sodium hydroxide solution, intermittently stir and soak for 12 hours, drain the soaking solution, wash with clean water until neutral, and then reuse.

In addition, for some gold containing ores with complex properties, raw ore roasting+full mud cyanide can be used; Methods such as bacterial leaching and full mud cyanidation.

Gold extraction by infiltration cyanide method

The infiltration cyanide method is also one of the cyanide leaching processes, which is based on the infiltration of cyanide solution through the ore layer to leach gold from gold bearing ores. It is suitable for sand mines and loose porous materials. The infiltration cyanide leaching method has two processes: pool leaching and heap leaching. The infiltration cyanide leaching solution is then treated with ion exchange resin, activated carbon adsorption, or zinc powder (wire) replacement.

Pool leaching gold selection process

Infiltration leaching is generally carried out in a filtration leaching tank, which usually uses a wooden tank, iron tank, or cement tank. The bottom of the pool is horizontal or slightly inclined, forming a circular, rectangular, or square shape. The pool is equipped with a false bottom made of perforated acid resistant plates, which is covered with filter cloth. The filter cloth is covered with a grid containing wooden or corrosion-resistant metal strips. During leaching, the ore is loaded into a pool, and a leaching agent is added above the pool. The leaching solution flows out from the lower part of the false bottom. False bottom is used for filtering and supporting ores.

The time required for leaching in a infiltration tank is not only determined by the dissolution rate of the solvent on minerals, but also closely related to the penetration rate of the solvent in the material layer. The infiltration rate mainly depends on factors such as loading height, material porosity, silt content, leaching agent viscosity, and the characteristics of the material itself.

Heap leaching gold selection process

Heap leaching mainly involves transporting the mined ore to a pre prepared yard for stacking, or directly stacking it on waste or low-grade ore. Cyanide leaching solution is sprayed or filtered to allow the solution to pass through the ore and produce a leaching effect. The leaching solution is circulated multiple times, repeatedly spraying the ore heap, then collecting the leaching solution, and then using ion exchange resin, activated carbon adsorption or zinc replacement. The lean solution is returned to the heap leaching operation for recycling.

The heap leaching site is generally selected as a gently sloping mountainous area close to the mining site and convenient for transportation (natural slope 5-15) ˚)， First, remove weeds and topsoil, then compact and build to a slope of 5 ˚ The left and right foundations, with a slightly lower height between the two sides, facilitate the concentrated flow of leachate into the storage tank. Geomembranes are laid on the storage yard to prevent leakage. Build a 0.4m soil embankment around the yard and create a waterproof ditch to prevent rainwater from entering the site. Before piling up ore, pile up large pieces of lean ore with a thickness of 0.3m.

The heap leaching method has low production costs, can be put into operation quickly, and the scale of heap leaching can be large or small. After crushing the ore to a certain particle size, heap leaching or granulation heap leaching is carried out.

Gold ore resources are extremely precious, and in order to select ores more reasonably, the gold ore beneficiation process is crucial. To select gold from gold ore in a more economical and environmentally friendly way, it is necessary to first conduct beneficiation tests, comprehensively analyze the properties of the ore, and obtain a scientific beneficiation test report to determine which gold ore beneficiation process to use. After considering the actual situation of the gold ore beneficiation plant, investment and other factors, the beneficiation plan should be determined to achieve the ideal investment return rate.