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Click to add WeChatmy country's gold ore resources are mainly composed of placer gold, rock gold and associated gold. Among them, the associated gold has a large proportion, and there are many types of gold ores and deposits. Most of the associated gold is generated in sulfide ores such as chalcopyrite, bornite and arsenopyrite. It is difficult to select this type of gold ore, and it is difficult to obtain a more ideal gold recovery rate using conventional beneficiation methods. Therefore, the beneficiation conditions can be improved through gold ore pretreatment methods to increase the gold recovery rate.
At present, the oxidation method is often used for the pretreatment of refractory gold ores, mainly including pressure oxidation method, bacterial oxidation method, roasting oxidation method and chemical oxidation method.
This method uses pressurized oxidation acid leaching or alkaline leaching to pretreat gold ore. Before operation, harmful impurities (such as sulfur, arsenic, antimony, etc.) in the gold ore must be removed to achieve a state where gold particles are completely exposed, and then the gold is recovered by cyanidation.
This method is not as sensitive to the sulfur content of the raw materials as natural roasting. In order to achieve the required sulfur content, it often leads to a decrease in the gold recovery rate of the beneficiation. However, this method is basically carried out in an acidic medium. However, in recent years, the application of tubular heat exchange reactors and catalysts has enabled the process to be carried out quickly at low pressure or even normal pressure.
Bacteria can oxidize and leach elements such as S, As, and Fe. Therefore, the use of bacterial oxidation can effectively expose the encapsulated gold, which is convenient for subsequent cyanidation gold extraction operations. The process is to carry out bacterial oxidation leaching in a stirring tank. In addition to continuously blowing air into the slurry, it is also necessary to add an appropriate amount of bacterial nutrients to ensure that the bacteria reproduce continuously. It is particularly important to keep the pH value of the slurry leached by bacteria strong acidity. This method has low cost, low energy consumption, light environmental pollution and good leaching effect.
This method is an early and mature gold pretreatment method. For low sulfide, arsenic, carbon, fine-grained gold ores with poor floatability, direct roasting can be used. This method can not only improve the recovery rate of gold, but also make full use of As and S in calcium-magnesium solidified ores, and can also achieve environmental protection and self-cleaning effects.
The process is: two-stage roasting, in which the first stage of boiling roasting is used to treat Cu or complex gold concentrate containing multiple metals. In the subsequent operation, the roasted sand can be used for acid leaching to extract copper and the final leaching residue can be sold as iron cement, and the flue gas produced can be purified to produce sulfuric acid; the second stage of boiling roasting is used to treat difficult-to-leach gold concentrate mainly containing high As and S. The difficulty of this method lies in the treatment after arsenic recovery and the pollution to the atmosphere.
This method is to oxidize the sulfide minerals in the gold ore with a strong oxidant, thereby exposing the gold from it. There are several chemical oxidation methods for pretreatment of gold, including chlorination method, nitric acid method and electrochemistry.
Chlorination oxidation method: Chlorine is used as an oxidant to oxidize difficult-to-treat gold ore. This method has an inhibitory effect on carbonaceous materials and a passivating effect on gold. Since liquid chlorine and chlorine gas easily form hypochlorous acid after dissolving in water, and hypochlorous acid is a strong oxidizing substance, it can oxidize carbonaceous materials and sulfide minerals in difficult-to-treat gold ores.
Nitric acid oxidation method: uses HNO3 as an oxidant. Under certain conditions of slurry, oxygen concentration and temperature, nitric acid can quickly combine with minerals containing Fe and S, thereby exposing gold in a cyanide environment. The purpose of pressurizing this process is usually to prevent the oxidation process from producing elemental sulfur.
Electrochemical oxidation method: In the slurry system containing conductive media such as sulfuric acid, hydrochloric acid and nitric acid, under the conditions of current 0.75~1A and voltage 6~6V, pyrite and arsenic iron ore are oxidized into easily soluble iron sulfate and iron arsenate through electrode reaction. At the same time, the porosity of the gold ore can be increased by 2~6 times. This technology has low environmental damage, high oxidation efficiency, and a very safe operation process.
In addition to the above four oxidation methods for pre-treating gold, there are also potassium permanganate method, dichromate method and Carrot acid method. However, no matter which pre-treatment method is used, it must be determined according to the properties of the gold ore and cannot be selected blindly. Therefore, it is recommended to conduct mineral processing tests. Through experimental analysis, designing suitable and reasonable gold ore pre-treatment methods and gold ore beneficiation process plans is the key to obtaining high recovery rates.
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