Wechat QR code
Wechat QR code
15311826613
Click to add WeChatFollowing the previous two articles on gold ore dressing and gold pretreatment, this article continues to introduce gold ore leaching technology. Gold ore leaching is an important means of gold selection. For fine-grained gold ores that are difficult to recover by gravity separation, flotation and other methods; or gold ores that have destroyed gold inclusions through pretreatment such as roasting, pressure oxidation, and biological oxidation; low-grade and simple gold ores can be further extracted by leaching to improve the comprehensive utilization rate of gold mines. The gold leaching process is to dissolve gold from the ore through a specific leaching agent to form a gold-containing solution, thereby separating gold from other impurities.
There are three main methods for common gold ore leaching processes, namely, full mud cyanidation, non-cyanide leaching and pressure oxidation. Let's take a look at these gold leaching processes and processes.
The full mud cyanidation method is a method of grinding the gold ore to fully expose the gold minerals, and then leaching with cyanide solution. It has high leaching efficiency, relatively simple process and convenient operation, but cyanide is highly toxic. During the leaching process, if cyanide leaks or is improperly handled, it will cause serious pollution to the soil, water and air, and endanger human health.
This gold mine processing technology is suitable for a variety of gold ores, especially fine-grained impregnated gold ores. Its process flow mainly includes the following steps:
Crushing: The raw ore after mining is first fed into the crusher for crushing. Its particle size is adjusted according to demand and is divided into coarse crushing, medium crushing and fine crushing. Among them, jaw crushers and cone crushers are mostly used for coarse crushing and medium crushing, mainly to crush large pieces of ore into smaller particles, and the general particle size is controlled at about a few centimeters; hammer crushers are mainly used for fine crushing.
Grinding: The crushed ore enters the ball mill and is further ground to a suitable particle size. It is usually required that the ore particle size reaches -200 mesh and accounts for 60%-90% to fully dissociate the gold minerals. The equipment usually uses a grid-type ball mill for coarse grinding and an overflow ball mill for fine grinding.
The ground slurry enters the stirring tank, and an appropriate amount of water is added to adjust the slurry concentration, which is generally controlled at 30%-50%. At the same time, lime and other adjusting agents are added to adjust the pH value of the slurry to 10-11 to create an alkaline environment conducive to cyanide leaching and inhibit the dissolution of other impurities.
Cyanide agents such as sodium cyanide (NaCN) or potassium cyanide (KCN) are added to the adjusted slurry. Under sufficient stirring conditions, cyanide reacts chemically with gold to form a water-soluble gold-cyanide complex. The leaching process is usually carried out in multiple stirring tanks in series, and the leaching time is generally 24-48 hours to ensure that the gold is fully dissolved.
The leached pulp is separated into solid and liquid by thickeners, filters and other equipment to obtain gold-containing precious liquid and leaching residue. The thickener uses the principle of gravity sedimentation to make the solid particles in the pulp settle to the bottom, and the supernatant is the gold-containing precious liquid; the filter further filters the bottom flow of the thickener to improve the effect of solid-liquid separation.
The methods for recovering gold from gold-containing precious liquid mainly include zinc powder replacement method and activated carbon adsorption method.
Zinc powder replacement: zinc powder is added to the precious liquid, zinc and gold cyanide complex undergo replacement reaction, gold is reduced to metallic gold and precipitated, and gold mud is obtained by filtration. The gold mud is then smelted and other processes to obtain crude gold.
Activated carbon adsorption method: activated carbon is added to the precious liquid, the gold cyanide complex is adsorbed by activated carbon, and then gold is recovered from the activated carbon through processes such as desorption and electrolysis.
The gold leaching residue needs to be properly treated as tailings to reduce pollution to the environment. Usually, the method of stockpiling or reuse is adopted. For tailings containing cyanide, detoxification treatment is required, such as using acidification method, hydrogen peroxide method, etc. to decompose cyanide into harmless substances.
Non-cyanide leaching method is a leaching method developed to reduce environmental pollution, and thiourea leaching method is a typical representative. In addition to thiourea leaching method, there are also thiosulfate leaching method, halide leaching method, etc. The common feature of these methods is that cyanide is not used, thereby reducing the harm to the environment.
Thiosulfate leaching method uses thiosulfate to form a complex with gold in an alkaline medium to achieve gold dissolution. This method has the advantages of fast leaching speed and environmental friendliness. Halide leaching method uses halides (such as chloride, bromide, etc.) to dissolve gold under certain conditions. The development of non-cyanide leaching method provides more options for gold leaching and helps promote the sustainable development of the gold mining industry.
Common non-cyanide leaching agents include thiourea, thiosulfate, halogen, etc. The following process flow is introduced using thiourea leaching as an example:
Similar to the full mud cyanidation method, the raw ore is crushed and ground to fully dissociate the gold minerals. The grinding particle size depends on the properties of the ore, and generally requires -200 mesh to account for 70%-90%.
The ground slurry enters the stirring tank, and an appropriate amount of water is added to adjust the slurry concentration, which is generally controlled at 20%-40%. At the same time, sulfuric acid and other adjusting agents are added to adjust the pH value of the slurry to 1.5-2.5 to create an acidic leaching environment.
Thiourea and oxidants (such as hydrogen peroxide, ferrous sulfate, etc.) are added to the adjusted slurry. Under stirring conditions, thiourea reacts chemically with gold to form a water-soluble gold-thiourea complex. The leaching time is generally 4-8 hours, and the leaching temperature is controlled at 30-50℃ to improve the leaching efficiency.
The leached pulp is separated into solid and liquid by filtering and other methods to obtain gold-containing precious liquid and leaching residue.
The main methods for recovering gold from gold-containing precious liquid include ion exchange method, electrolysis method, etc.
Ion exchange method: use ion exchange resin to adsorb gold thiourea complex, then desorb gold from the resin by desorbent, and then further process to obtain gold products.
Electrolysis method: pass the gold-containing precious liquid through the electrolytic cell, and under the action of direct current, the gold ions are reduced to metallic gold on the cathode.
The leaching residue also needs to be properly treated, and can be comprehensively utilized or stored according to its composition and properties. Since the waste residue generated during thiourea leaching is relatively less toxic, it is relatively easy to handle.
The pressure oxidation method is a method of oxidative leaching under high pressure conditions. In a high-pressure environment, the solubility of oxygen increases, the reaction rate accelerates, and the gold recovery rate can be effectively improved. The pressure oxidation method is suitable for treating difficult-to-treat gold ores containing sulfur and arsenic. Through high-pressure oxidation, sulfides and arsenides can be oxidized and decomposed to expose gold and increase the leaching rate of gold.
The pressure oxidation method has high leaching efficiency and strong adaptability. It can treat some complex gold ores that are difficult to treat by traditional leaching methods, expanding the scope of utilization of gold resources. However, the pressure oxidation method requires special high-pressure equipment, with high investment costs, high maintenance and operation requirements for equipment, and a high-temperature and high-pressure environment will be generated during the high-pressure oxidation process, which poses certain safety risks.
The pressure oxidation method is mainly used to treat difficult-to-treat gold ores containing sulfur and arsenic. Its process flow is as follows:
The raw ore is crushed and ground to make the ore particle size reach a suitable range, generally -200 mesh accounts for 80%-95%, to ensure that the ore can fully react during the pressure oxidation process.
The ground slurry enters the stirring tank, and an appropriate amount of water is added to adjust the slurry concentration, which is generally controlled at 15%-35%. At the same time, according to the properties of the ore, add appropriate amounts of additives, such as sulfuric acid, catalysts, etc., to promote the oxidation reaction.
Pump the adjusted slurry into the autoclave, pass oxygen or air, and under high temperature (180-250℃) and high pressure (1-5MPa) conditions, the sulfides (such as pyrite, arsenopyrite, etc.) and arsenides in the ore are oxidized and decomposed to produce sulfates, arsenates and other substances, and the gold wrapped in them is released. The oxidation reaction time is generally 1-3 hours.
The oxidized slurry is discharged from the autoclave and enters the flash tank. The temperature and pressure are reduced by flash evaporation, so that the steam in the slurry evaporates rapidly and part of the heat is recovered at the same time.
The slurry after flash evaporation enters the neutralization tank, and neutralizers such as lime are added to adjust the pH value of the slurry to a suitable range (generally 6-8) to neutralize excess acid and precipitate metal ions such as iron and aluminum. Then, the soluble salts and impurities in the slurry are washed away by multi-stage countercurrent washing to obtain relatively pure oxide slag.
After the oxide slag is slurried, the gold is leached by conventional cyanide leaching or non-cyanide leaching methods. The subsequent solid-liquid separation, gold recovery and tailings treatment steps are similar to the full mud cyanide method or non-cyanide leaching method.
The above introduces three gold leaching technologies and processes. The gold leaching process is a key step in the gold selection operation, which is of great significance in improving the gold recovery rate and realizing efficient resource utilization. Different gold leaching processes can adapt to various types of gold mines. Whether it is an oxide ore, a sulfide ore or a complex polymetallic ore, a suitable leaching method can be found.
Consultation
153-1182-6613
Consult
Message
