January 27, 2021

Research status of leaching technology for refractory gold ore

In recent years, as the world economy, China's gold reserve has reached 1054 tons. At present, China's gold resources are 1.5 to 20,000 tons, and the reserves of gold are 4634 tons, including 2,786 tons of rock gold, 593 tons of sand gold, and 1,255 tons of associated gold. The proven reserves rank seventh in the world. However, about 1,000 tons of these proven gold resources are refractory gold mines, accounting for nearly a quarter of the total.

The refractory gold ore refers to a gold ore that has not been effectively leached by conventional cyanidation after the ore has been finely ground. The gold in this type of gold ore cannot be contacted with cyanide solution due to physical encapsulation or combination of chemicals, resulting in a low leaching rate. The refractory gold ore is divided into three types: (1) non-sulfide gangue wrapped gold, the gold particles in this ore are too small to be dissociated by grinding, and the gold particles are difficult to contact with cyanide; (2) gold wrapped in pyrite and arsenopyrite sulphide minerals and the like, the gold particles are finely ground nor can package contacting the leachate; (3) a carbonaceous gold ore, while leaching of gold, gold cyanide complex and an organic ore is activated The charcoal is "jacked" from the solution.

First, the pretreatment of difficult leaching ore

The leaching rate of most of the refractory ore directly under stirring and leaching with sodium cyanide is about 10% to 20%, and the leaching rate is low. The researchers have greatly improved the leaching rate of refractory gold ore by pre-treating the raw materials. Specific methods include oxidative roasting, hot pressing oxidation, biological oxidation, and nitric acid catalytic oxidation.

(a) roasting

Calcination can decompose sulfides, arsenic and antimony volatilize in an oxidized state, inactivate carbonaceous materials, and microscopically finely form gold enrichment. The process has the advantages of strong adaptability, low operating cost and good comprehensive recovery effect. The disadvantage is that it is easy to cause over-burning and under-burning, and the generated SO 2 and As 2 O 3 will pollute the environment.

Commonly used roasting methods in production include two-stage roasting, solid-sulfur solid-arc roasting, and pellet coating roasting.

The two-stage roasting process uses two roasting furnaces, the first stage is low-temperature roasting, and the temperature is 450-500 ° C, which is mainly used for removing arsenic. The second stage is high temperature oxidation, the temperature is 600 ~ 650 ° C to remove sulfur; solid sulfur solid arsenic roasting is the addition of fixative to make the arsenic in the ore sample to form sulfate and arsenate, the process does not emit toxic gases, but also The wrapped gold is fully exposed. Fixing agents used are calcium oxide, calcium hydroxide, sodium carbonate, sodium hydroxide, magnesium oxide, magnesium carbonate and the like; Pellet firing pellet is arsenic sulfur concentrate and a binder formed on a surface covered by a A coating layer composed of an arsenic sulfur fixative, As 2 O 3 and SO 2 gas generated during calcination are wrapped with calcium arsenate and calcium sulfate formed by a fixing agent to prevent outward diffusion and pollute the environment.

(2) Hot pressing oxidation method

The hot pressure oxidation method is divided into acidic hot pressure oxidation and alkaline hot pressure oxidation. Alkaline hot pressure oxidation is only suitable for refractory gold ore with high carbonate content and low sulfide content (<20%). Acidic hot pressure oxidation is a series of reactions of pyrites such as pyrite and arsenopyrite with oxygen in an acidic medium under high temperature and high pressure conditions. The gold encapsulated after the change of mineral structure is exposed, which is favorable for cyanidation gold.

The hot pressure oxidation process is a wet process, smokeless gas pollution. The oxidation products of pyrite and arsenopyrite are all soluble, so gold particles can be dissociated regardless of size, and the recovery rate of gold is high. After many hot-dip leaching of refractory gold concentrate, the leaching rate is over 98%. .

(3) Biological oxidation pretreatment

The basic principle of the biological oxidation pretreatment process is to decompose the metal sulfide minerals by the action of biological enzymes to dissociate the gold minerals. Biological oxidation is generally classified into tank oxidation and heap oxidation. The advantage of this process is that it does not generate harmful gases such as SO 2 and As 2 O 3 , has low investment, low cost, is safe and clean, and is easy to operate.

The experiment proves that the gold leaching rate of a high-sulfur and high-arsenic gold concentrate can be increased from 15.02% to 94.17% in the conventional leaching process by the bacterial oxidative cyanidation process, and the leaching effect is obvious.

(4) Nitric acid catalytic oxidation pretreatment

The oxidation effect of nitric acid on pyrite, arsenopyrite and non-ferrous metal sulfides is very obvious. The catalytic oxidation of nitric acid is divided into HMC method, Arseno method, Redox method and nitrox method. However, heating and pressurization are required in the process of nitric acid oxidation, so the process is not industrialized.

In the test, a high-arsenic refractory gold ore was treated by nitric acid oxidation leaching-carbon slurry cyanide-cyanide flotation flotation. The recovery rate of gold increased from 34% in direct cyanidation to 94% to 96%.

(5) Microwave roasting pretreatment

Microwaves can selectively heat minerals. When the thermal stress generated between useful minerals and gangue minerals increases sufficiently, cracks are formed at their interfaces, promoting the dissociation of useful minerals. The advantage of this process is that the calcination time is only about fifteen minutes and the temperature is low, avoiding the generation of SO 2 and As 2 O 3 . The experiment proves that the leaching rate of gold in the refractory gold concentrate after microwave treatment can be increased from 30% to over 90% when untreated.

(6) Other pretreatment processes

Li Shaoqing and other researchers at Chang'an University pretreated with an alkali mixture before cyanide leaching a high- copper , high-arsenic, high-sulfur gold ore, and added the activator SMD during the cyanidation process. The leaching rate reached 97.8. % is better than the leaching rate of conventional cyanidation (48% to 54%). However, this method is too targeted, and the amount of sodium cyanide is large, which needs to be widely applied and needs further study (9) .

Second, the strengthening of cyanide leaching

(1) Multi-stage leaching

The multi-stage leaching means that the solution saturated with the impurity ions is discharged after each leaching, and the cyanide leaching is performed again by adding water or a solution containing less impurity ions, and the number of leaching stages depends on the leaching index. This process is mainly used to treat refractory gold ore containing cyanide soluble impurities.

(2) Charcoal leaching method

The carbon leaching method refers to the simultaneous completion of cyanide leaching of gold and adsorption of ions on activated carbon in the same tank. At the same time as cyanidation gold, an excessive amount of activated carbon is added to the leachate to compete with the carbonaceous material for adsorption to reduce or eliminate the harmful effects of the carbonaceous material, so it is difficult to treat the presence of substances capable of adsorbing gold in the ore. Dip gold ore.

(3) Pressurized cyanidation

Pressurized cyanide is a means of enhancing the kinetics of the leaching process, which increases the reaction temperature and activates the mineral lattice to facilitate the leaching process. This process is particularly suitable for the treatment of refractory gold ores containing bismuth. Yan Yanjun's process of pressure cyanide leaching and extraction of gold from ore, increasing the O 2 content of the leaching solution by changing the pressure of the leaching process, the leaching time was shortened from 24h to 45min; the gold leaching rate reached 93.2%, which was lower than the unpressurized It increased by 19.6%.

(4) Stirring strengthening

Stirring strengthening is to strengthen the immersion gold process by changing the stirring conditions, and to improve the leaching rate of gold. Commonly used stirring methods include vigorous stirring, shaking stirring, pulse stirring, and the like. Experiments have shown that the leaching rate of a certain gold ore can be increased from 73.45% to 90.5% by means of oscillating stirring.

Third, non-cyanide method

Because cyanide is highly toxic, researchers have been conducting research on non-cyanide leaching. Currently common methods include thiourea method, thiosulfate method, halogenation method, ammonium polysulfide method and organic nitrile method. These methods have the common advantages of low environmental pollution and short leaching time, which is about one-third of the reaction time of the cyanidation reaction. However, each method has disadvantages, the thiourea method and the thiosulfate method leaching agent are used in a large amount, and the production cost is high; the selectivity of the halogenation method is poor; the stability of the ammonium polysulfide is poor, and the total recovery of gold from the leachate is difficult; the organic nitrile Volatile, some toxic. These shortcomings lead to the application of non-cyanide method in industry, and most of them are in the experimental research stage.

Fourth, the conclusion

In the three methods of gold extraction from refractory gold ore: pretreatment method, enhanced cyanidation method and non-cyanide method, pretreatment is a commonly used method. The roasting process is polluted and the biooxidation method takes a long time, so the chemistry Oxidation is the most valuable application. Enhanced leaching is very effective in the treatment of some medium-difficult gold ore. In the industry, carbon leaching has been used to treat carbonaceous clay- like gold ore and multi-stage leaching to treat copper-bearing gold ore. Non-cyanide leaching technology will become a development trend of gold extraction due to its low pollution.

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