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How to Extract Gold From Ore: Beneficiation Methods and Machines
2022-03-18 Xinhai (396)
2022-03-18 Xinhai (396)
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Gold ore is generally divided into gravel ore and rock gold ore, among which gravel ore accounts for 20%. Gold extraction refers to the processes required to extract gold from ore. Due to the different types of ore, the nature of the ore is also different, so the beneficiation process needs to be customized.
Common gold ore beneficiation processes mainly include cyanidation, flotation, gravity separation and Amalgamation.
The cyanidation method is one of the main methods of gold ore beneficiation, which can be divided into two categories: agitation cyanidation and percolation cyanidation. Agitation cyanidation is mainly used for the treatment of flotation gold concentrate, or in the all-slime cyanidation, while percolation cyanidation is mainly used for the treatment of low-grade gold-bearing oxide ores.
Agitation cyanidation gold extraction process mainly includes two types:
One is the cyanidation-zinc replacement process (CCD method and CCF method) that recovers gold by replacing precipitation with zinc powder (wire) through continuous countercurrent washing.
The other is the non-filtering cyanide carbon slurry process (CIP method and CIL method) that uses activated carbon to directly absorb and recover gold from the cyanide pulp without filtering and washing.
a. Cyanidation-Zinc Replacement Process (CCD Method and CCF Method)
The cyanidation-zinc replacement process (CCD method and CCF method) is used to treat gold-bearing solution after leaching. The principle is to use zinc powder (wire) as a reducing agent to replace gold and silver from the leaching solution.
The process mainly include countercurrent washing solid-liquid separation, leaching solution purification, deoxidation and zinc powder (wire) replacement.
◆ Countercurrent washing solid-liquid separation: Separation of the gold/silver bearing solution after leaching (leaching solution) from the solid.
◆ Leaching solution purification: Remove the suspended matters in the gold/silver bearing solution (leaching solution), so that the gold-bearing solution entering the replacement operation reaches a clear and transparent state.
◆ Deoxidation: Remove the dissolved oxygen in the gold/silver bearing solution (leaching solution).
◆ Zinc powder (wire) replacement: Replace the precious metal in the gold/silver bearing solution (leaching solution) with zinc powder (wire) to form gold (silver) mud.
b. Carbon in Pulp/Leach Gold Extraction Process (CIP method and CIL method)
The carbon in pulp /leach gold extraction process (CIP method and CIL method) is to put activated carbon into the cyanide slurry, adsorb the dissolved gold on the activated carbon, and then extract the gold from the activated carbon.
This process mainly including leaching raw material preparation, agitation leaching and countercurrent carbon adsorption, gold-loaded carbon desorption, electrowinning, smelting ingot, carbon regeneration and other operations.
◆ Preparation of leaching raw materials: including physical crushing, grinding and classification. Generally, the particle size of the overflow after grinding and classification of the carbon in leach gold extraction process is mostly -200 mesh, accounting for 85-95%.
◆ Debris-removal operation: Sawdust, grass roots and other debris in the slurry can easily cause clogging of the pipe and screen and will absorb gold, so they must be removed before leaching.
If necessary, we need to concentrate the slurry and add descaling agent into it. Descaling agent can reduce the scaling on the surface of the activated carbon and the screen.
In general, two times of debris-removal operations are necessary in grinding process, respectively, in the first and the second stage grinding classification overflow. Intermediate frequency linear vibrating screens are widely used as debris-removal equipment, in the first debris-removal operation, spiral screen and drum screen are also can been seen, debris-removal sieve pit size should be as small as possible，but must ensure the slurry can flow through the sieve easily.
◆ Pre-leaching thickening operation: When the overflow concentration of grinding and classification is mostly 18-22%, it is not suitable for direct leaching, and the slurry must be thickened.
◆ Agitation leaching and countercurrent carbon adsorption: In the CIP process, leaching and adsorption are two independent operations. In the adsorption operation, the leaching process has been basically completed, and the size, number and operating conditions of the adsorption tank are determined by the adsorption parameters.
In the CIL process, the leaching and adsorption operations are carried out at the same time. Generally speaking, the leaching operation takes longer than the adsorption operation, so the size of the tank, aeration and dosing are determined by the leaching parameters. Since the 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 at the same time, 1-2 stages of pre-soaking are usually added before leaching and adsorption.
◆ Gold-loaded carbon desorption and electrowinning electrolysis: Gold-loaded carbon and slurry are lifted to a carbon separation screen (usually a linear vibrating screen) through an air lifter, and washed with clean water on the screen to separate the carbon from the slurry. The gold-loaded carbon enters the carbon storage tank, and the ore slurry and washing water enter the adsorption tank of the first stage.
At present, the commonly used gold-loaded carbon desorption method is high temperature and high pressure desorption method, that is, adding the anion that is easy to be adsorbed by activated carbon to the desorption system to replace Au(CN)2- to realize the desorption of gold and recover the liquid by the electrolysis method to obtain solid gold.
◆Smelting ingot：After pickling and removing impurities, the gold mud can be directly smelted to produce gold ingots. Using hydrometallurgy, the purity of gold ingots can reach more than 99.99%.
◆Carbon regeneration: After the activated carbon is adsorbed and desorbed, it needs to be regenerated to restore its good adsorption performance.Generally, we need to treat the desorbed activated carbon with acid pickling to remove accumulations such as carbonates firstly, then thermally activate the carbon to restore the adsorption activity of it to make it can be reused. The main equipment includes activated carbon regeneration kiln, water quench tank, fine carbon separation screen, etc.
c. Cyanidation-ion Exchange Resin Adsorption Method for Gold Extraction
The ion exchange resin adsorption method is basically similar to the leaching and adsorption process of the CIP/CIL method. The difference is that the carbon is replaced with ion exchange resin. This process includes operations such as gold-loaded resin desorption electrolysis, smelting ingot, and resin regeneration.
◆ Desorption and electrolysis of gold-loaded resin: The gold-loaded resin and pulp are lifted to the resin separation screen (usually a linear vibrating screen) through a pump or an air lifter, and washed with water on the screen to completely separate the resin from the pulp. Then the gold-loaded resin enters resin storage tank while ore pulp and washing water enter the adsorption tank of the first stage.
Afterwards, we feed the cleaned gold-loaded resin into the desorption column, add the desorption solution, and carry out 36 hours of cycle operation at a temperature of 40-60°C. The desorbed gold-bearing solution enters the electrolytic cell to get the gold mud by electrolysis method.
◆ Smelting ingots: After pickling and removing impurities, the gold mud can be directly smelted to produce gold ingots. Using hydrometallurgy, the purity of gold ingots can reach more than 99.99%.
◆ Resin regeneration: The desorbed resin needs to be regenerated to recover its good adsorption performance.
In addition, for some gold-bearing ores with complex ore properties, we can use the methods of roasting raw ore + all-slime cyanidation or bacterial leaching + all-slime cyanidation.
The percolation cyanidation method is also one of the cyanide leaching processes. Its principle is that the cyanide solution penetrates through the ore layer to leach the gold from the gold-bearing ore. It is suitable for alluvial and loose porous materials.
There are two kinds of percolation cyanidation methods: pool leaching and heap leaching.
After the cyanide leaching solution percolate and leach the gold out, we can then treat the gold-bearing solution with ion exchange resin, activated carbon adsorption or zinc powder (wire) replacement to get the gold mud.
a. Pool Leaching Process
The percolation leaching is generally carried out in the percolation leaching tank, which usually is a wooden tank, an iron tank or a cement tank. The bottom of the pool is horizontal or slightly inclined, round, rectangular or square.
The leaching tank is equipped with a false bottom made of a perforated acid-resistant plate. The false bottom is covered with filter cloth, and the filter cloth is covered with a grid with wooden or corrosion-resistant metal strips.
When leaching, we load the ore in the tank, and add the leaching reagent to the top of the tank. The leaching solution flows out from the lower part of the false bottom. The false bottom is used to filter and support the ore.
The penetration rate mainly depends on factors such as the height of the material, the porosity of the material, the degree of mud content, the viscosity of the leaching reagent, and the characteristics of the material itself.
b. Heap Leaching Process
The process of heap leaching is mainly to transfer the mined ore to a pre-prepared storage yard for pile, or directly pile on the waste rock or low-grade ore, the spray or infiltrate the cyanide leaching reagent, so that the reagent can pass through the ore and make the gold in it be leached.
After the leaching solution repeatedly circulated and sprays the ore pile, we can collect the leaching solution, and then using ion exchange resin, activated carbon adsorption or zinc replacement to get gold mud, the solution without gold can be returned to the heap leaching operation for recycling.
The heap leaching site generally is a gentle slope mountain (natural slope 5-15˚) close to the mine site and convenient for transportation. After removing the weeds and floating soil first, we should then compact the soil to build a foundation with a slope of about 5˚, with the two sides high and the middle slightly lower, which is convenient for the leaching solution to flow into the storage tank in a concentrated manner, and then cover the storage yard with a geomembrane to prevent leakage. Then we build a 0.4m soil ridge around the storage yard and use it as a waterproof ditch to prevent rainwater from flowing into the yard. Before piling up the ore, we can pile up the 0.3m thick lean ore first.
The heap leaching method has low production cost and can be put into production quickly, and the heap leaching scale can be large or small. After the ore is crushed to a certain size or granulated, it can be piled to get leached.
Flotation is a beneficiation method widely used in a plant for processing gold. It is often used to process gold-bearing sulfide minerals with high floatability. Float gold into copper and lead concentrates, and then extract gold from these concentrates. Therefore it's a relatively economical and reasonable process for gold ore containing ferrous metals in the original ore, which can realize the comprehensive utilization of multiple metals and enrich the gold in sulfide minerals as much as possible.
In order to increase the rate of return on investment, the beneficiation process combining flotation and other processes can sometimes achieve more impressive results for ores of different properties.
a. Flotation-Cyanide leaching of concentrate
This gold beneficiation method is often used to process gold ore containing gold-bearing quartz veins and gold-bearing golden iron ore veins. Generally, we use xanthate for a collector and terpineol for a foaming agent to float the weakly alkaline slurry in the flotation machine and obtain gold concentrate. Then the flotation concentrate is leached again by cyanide, which makes the gold dissolve by cyanide and the complex enter the solution, and then replaced with zinc powder to obtain gold mud, and finally the gold mud is smelted to obtain pure gold.
b. Flotation-Thiourea leaching of concentrate
For vein gold ore with high arsenic and sulfur or high carbon and argillaceous, we can use the flotation method to obtain gold-containing sulfide concentrate, and then leach the flotation concentrate with thiourea to recover gold.
The thiourea method for gold extraction is a new low-toxic gold extraction process which is improving day by day. The thiourea acid solution dissolves gold and silver at a high speed, low toxicity, and easy to regenerate. Antimony, arsenic, copper, sulfur and other mineral components are not sensitive to gold extraction by thiourea, but will affect it by cyanidation. Therefore, thiourea leaching can extract gold and silver from gold-bearing minerals that are difficult to treat by cyanidation. At the same time, the time of thiourea leaching is generally much shorter than cyanide leaching.
c. Flotation-Concentrate roasting-High acid washing-Cyanide leaching
For flotation concentrates containing high arsenic and sulfur, after flotating the cyanide tailings, sulfur, iron, arsenic and other impurities are enriched in the concentrate to become difficult to select high-sulfur and high-arsenic concentrates, and cannot be directly cyanided. In this situation, we can put the flotation gold concentrate in the process of oxidative roasting first to remove arsenic and sulfur, so that the structure of the calcine after roasting is loose, which is more conducive to the leaching of gold and silver. Subsequently, using high acid pretreatment and washing, most of the impurities are dissolved by acid and removed by washing, ensuring the cyanide leaching rate and effectively enriching the gold grade.
Gravity separation method is the process of using the difference in the density and particle size of minerals to create suitable loose stratification and separation conditions by means of the combined action of medium fluid and various mechanical forces, so as to obtain products with different densities or different particle sizes. Since most gold-bearing ores contain a certain amount of coarse-grained free gold (+0.1mm), it is difficult to recover by flotation and hydrometallurgy. Therefore, the gravity separation method is mostly used to select placer gold and vein gold before and after flotation and leaching to recover coarse-grained gold from monomer dissociation. Generally, the lower limit of the particle size of gold that can be recovered by the gravity separation method is 0.01 mm.
a. Gravity beneficiation process of placer/alluvial gold ore
◆ Jig for gold extraction
◆ Shaking table for gold extraction
◆ Chute for gold extraction
b. Vein gold gravity separation methods
◆ Gravity separation-Cyanide combined process
◆ Gravity separation-Flotation combined process
◆ Flotation-Gravity separation combined process
Amalgamation can be divided into inner and outer type according to processing methods. Amalgamation is commonly adopted to separate gold from heavy concentrates at placer gold mine. While at vein gold mine, it is generally regarded as a part of combined processing to coordinate with flotation, gravity concentration and cyaniding, which is mainly used for collecting coarse monomeric gold.
To protect the environment from pollution and keep the workers' health, amalgamation shall be restricted for use. It has been forbidden in some foreign countries, and it is not commonly used in our country except for some individual and local small-scale gold mine.
◆ The high-efficiency, low-consumption and fast desorption electrolysis system
◆ The double impeller leaching agitation tank
◆ Zinc powder displacement device
◆ Two-layer (three-layer) washing thickener
◆ Air lifter
◆ Carbon screeen
◆ Suction mechanical agitation flotation cell
◆ Air inflation mechanical agitation flotation cell
◆ Jig
◆ Shaking Table
◆ Spiral Chute
The above teaches you how to extract gold from ore. If you have additional questions or would like a complete solution for your gold processing plant, you can contact our online service.
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