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1 physical pretreatment method
The only way to do this is through fine grinding, such as fine grinding to 100% < 28 um or ultra-fine grinding using a conventional mill to achieve a discharge size between 10 and 20 um. Commonly used ultra-fine grinding equipments include vibrating mills, agitating mills and jet mills. According to the required particle size and the energy input, the agitator mill is the most cost-effective, and it is mainly used for fine grinding of medium-difficult materials. The energy of the sorting is generally limited to the enrichment of high-grade materials rather than the entire feed. Currently used in Western Australia Carl Gori (Kolgoorle) close nyuk Leicester plant, which is used to deposit the gravity generated by the leached refractory pyrite re-grinding, so that the intake cycle People leaching.
2 Chemical oxidation pretreatment method
Several methods of wet oxidation can be used to oxidize metal sulfides, the most famous of which is pressurized oxidation. The high pressure oxidation process is discussed separately in another section, and this section will discuss the sorting at smaller external pressures. The nitrification/oxidation method, the Arteh/Cashman method, the activated oxidation method, the Kelvin acid method, and the slurry electrochemical method all use an acidic medium to destroy the matrix structure of the sulfide mineral to dissociate the gold. These methods do not use neutralization cyanidation leaching, but can be leached under acidic conditions using thiourea, chlorine, and bromine as leaching agents. However, the leach residue is still neutralized before it is discharged. Activated oxidation, nitrification/oxidation, and Arteh/Cashman processes have been studied on a pilot plant scale for oxidative conditions that are weaker than those in high pressure oxidation processes. Ultra-fine grinding is used in the activated oxidation method to obtain effective cleavage of the crystal lattice under mild conditions; nitrification oxidation method is oxidized by nitric acid; Arteh/Cashman's law is a hydrochloric acid pressure immersion filtration process, in which Ca is present in the solution . Kraft acid has been used as an oxidant on a laboratory scale (pressure: atmospheric pressure; temperature 60-80 ° C). A sorting study was conducted on metal sulfide ore. The electrochemical treatment of the arsenopyrite slurry is still only at the laboratory level.
3 roasting oxidation pretreatment method
The pretreatment of the heat can destroy the phase of the sulfide, thereby dissociating the gold. Calcination is the process of heating a sulfide to form an oxide under aerobic conditions; and high temperature pyrolysis is a process of heating a sulfide to convert it into a series of different reaction products under anaerobic conditions.
Roasting oxidation process features:
(1) The process is fast and adaptable, especially for ores containing organic carbon.
(2) By-products can be recycled and used to recover associated elements such as arsenic and sulfur.
(3) During the roasting process, it will cause “underburning†or “overburning†of the sulfide ore, which will affect the leaching rate of gold.
(4) The roasting process produces a large amount of harmful gases such as sulfur dioxide and arsenic trioxide, and the dust collecting system is complicated.
(5) The process conditions of the process are strictly controlled and the production and commissioning cycle is long.
(6) Due to the influence and restriction of the sulfuric acid market, the fluctuation of acid price directly affects the economic benefits of the process.
4 hot pressure oxidation pretreatment method
The hot-pressure oxidation method mainly uses high-temperature oxidation process in the autoclave by air or oxygen enrichment. The crystals of the sulfide ore and some gangue minerals are destroyed by means of heating and oxygenation, and the gold encapsulated by it is exposed to obtain cyanide. Leaching. The process can be carried out either in an acidic medium or in an alkaline medium; it can handle both raw ore concentrates and concentrates. The hot-pressure oxidation process has been successfully used in industrial production, and nearly 10 gold-plating plants using the process have been established in the United States, Canada, Brazil, and Papua New Guinea.
Characteristics of refractory gold ore hot pressing oxidation process:
(1) low of harmful impurity elements antimony, lead and other sensitivity.
(2) The process can directly treat raw ore, which is more effective for gold ore that is not easily floated and enriched.
(3) Due to the wet process, there is no smoke pollution problem.
(4) It is not good for materials with high organic carbon.
(5) The design and material requirements of the process equipment are very high, so the operation and maintenance level requirements are higher, and the capital construction investment cost is higher.
Hot-pressure oxidation is considered to be the most effective pretreatment process in Latin America. It is divided into acidic hot pressure oxidation and alkaline hot pressure oxidation. Acid hot-pressure oxidation is based on the mechanism that the sulfide minerals such as pyrite and arsenopyrite react with oxygen under high temperature and high pressure to change the mineral structure. The gold-coated sulfide is oxidized by a series of reactions under high temperature and high pressure in an acidic medium, and the gold mineral is exposed to achieve the purpose of cyanidation gold. The degree of oxidation of the sulfide depends on the temperature, pressure, oxygen flow and slurry concentration of the process. In 1985, the McLaughlin gold plant in the United States applied the pressurized autoclave to the ore for the first time. The plant uses three sets of pyrite-type gold ore with a sulfur content of 3% and a gold content of 5.8 g/t with a diameter of 4.2 m and a height of 1.6 m, and a treatment capacity of 2700 t/d. The ground slurry is first treated with an acid solution obtained by washing the oxidized pulp to decompose most of the carbonate in the material before entering the autoclave. Then, it is oxidized under the conditions of a temperature of 160 to 180, an oxygen partial pressure of 140 to 280 kPa, and a residence time of 90 minutes, and the sulfur oxidation rate is 85% or more. In order to reduce the amount of steam, it is required to recover heat from the slurry discharged from the autoclave. The autoclave casing is made of carbon steel, lined with lead plates and 2 layers of acid-resistant bricks. Each chamber is stirred with a blender of titanium shaft and ceramic blades. After the ore is treated, the cyanidation leaching rate of gold can reach more than 90%. Subsequently, the United States, Canada, Brazil and Papua New Guinea and other countries have established nearly 10 gold extraction plants using the process. The size of the acidic autoclave for processing raw ore is mostly above 1000t. For example, the GoldstrikeGetchel in the United States has a processing capacity of 2730t/d. Manufacturers of concentrates using this process are SaoRenton in Brazil, Porgora and Lihir in Papua New Guinea, and Campbell in Canada. Alkaline hot-pressure oxidation is the oxidative destruction of sulfide minerals formed by gold in a weakly corrosive alkaline system. The equipment has low requirements on materials. Its technical characteristics are suitable for the treatment of high carbonate content and low sulfide content. Difficult to handle gold ore.
5 Treatment of arsenic-containing refractory gold ore
(1) Arsenic removal by roasting oxidation
Arsenic in gold ore seriously affects the extraction of gold, so it is generally necessary to reduce arsenic. In high-arsenic and high-sulfur gold concentrates, because gold is encased by pyrite and arsenopyrite, the physicochemical properties of the high-arsenic and high-sulfur gold concentrates can usually be changed by roasting to destroy the original structure, thereby increasing the cyanide leaching rate of gold. The roasting oxidation method mainly includes rotary kiln roasting and boiling furnace roasting. The process is divided into one-stage roasting or two-stage roasting, and can also be divided into neutral roasting or oxygen-enriched roasting. Many scholars have studied roasting and arsenic removal techniques, such as Xiong Damin et al. The roasting of a high arsenic gold concentrate was carried out under the atmosphere. The results showed that the arsenic removal rate of the ore was 97.32%. The two-stage rotary kiln roasting process is used to remove arsenic from the arsenic concentrate in Huang, Hunan. The process is as follows: arsenic removal under anoxic conditions, the arsenic removal rate is 99.16%; then in aerobic Under the conditions of desulfurization, the final produced porous calcined cyanide leaching rate of up to 93%.
(2) Microbial oxidation for arsenic removal
Microbial arsenic removal pretreatment is a new process, especially suitable for the treatment of arsenic-containing carbonaceous gold ore. The method can oxidize arsenopyrite and pyrite in gold ore to soluble sulfuric acid, sulfate and arsenate. The related mechanism is: 1) Thermodynamically, arsenic can be oxidized by oxygen or ferric iron to pentavalent arsenic; 2) trivalent arsenic is stable during microbial oxidation, and arsenic can be added by adding an oxidant such as ozone. Oxidation.
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