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Click to add WeChatArsenic is a mineral element that is widely present in the earth's crust, but the presence of arsenic is almost always harmful, affecting the selection of other useful minerals, especially arsenic in gold ore. When the arsenic content reaches more than 0.1%, it is called arsenic gold ore, which is a typical difficult-to-process gold.
In order to effectively obtain gold minerals, effective arsenic removal is the key, so what are the gold extraction process methods for arsenic gold ore? At present, the available gold ore arsenic removal and gold extraction processes include: flotation method, oxidation roasting-cyanide leaching method, bacterial oxidation-cyanide leaching method, non-cyanide leaching method, etc. Let's learn about it together!
Flotation is used to select arsenic-containing gold ores, mainly for gold minerals that do not use arsenic sulfides as carriers. Gold-containing sulfide ores are separated from arsenopyrite by flotation. The key to high flotation efficiency is the selection of efficient gold collectors and effective arsenic inhibitors. Currently available gold collectors include mercapto anion type, thioesters and amino acids; arsenic inhibitors include lime combination inhibitors, strong oxidizing inhibitors, carbonate inhibitors, sulfur oxide inhibitors and organic inhibitors.
The roasting oxidation-cyanide leaching process is to roast the arsenic-containing gold ore under high temperature conditions, and use the action of air or oxygen to oxidize and decompose the arsenic sulfide wrapped in gold, so that the wrapped gold can be exposed, and then the gold is cyanide leached to improve the gold recovery rate. There are three methods for gold roasting: traditional roasting, solid arsenic roasting and two-stage roasting.
Traditional roasting gold extraction: The traditional rotary kiln roasting oxidation method is adopted. Under suitable process conditions, roasted sand with an arsenic content of only 0.109% can be obtained, and the arsenic volatilization rate reaches 98.85%. This process will produce a large amount of toxic gases such as SO2, As2O3 during the roasting process, which will damage the surrounding environment and require dust collection and purification equipment, but the cost is relatively high.
Solid arsenic roasting gold extraction:This method is also called alkali roasting. It is an improvement on the traditional roasting process. It not only retains the advantages of traditional roasting, but also effectively fixes harmful impurities such as sulfur and arsenic in the roasted sand (rather than volatilizing in the form of smoke) by adding alkali, and effectively avoids environmental pollution.
Two-stage roasting gold extraction:During the roasting process, the composition of the atmosphere affects the oxidation of arsenic minerals to a certain extent. If there is insufficient oxygen, the arsenic in the gold ore will volatilize in the form of As2O3; if there is sufficient oxygen, it will exist in the form of As2O5, and As2O5 can react with alkaline oxides to form non-volatile arsenates that remain in the roasted sand. If only one-stage roasting is used to treat gold concentrate with high arsenic content, the roasting temperature and oxygen content are difficult to control, and under-burning or over-burning often occurs. Two-stage roasting can effectively solve this problem. Among them, one stage uses a neutral or weakly oxidizing atmosphere to remove arsenic at a temperature of 400-600℃; the second stage uses an oxidizing atmosphere to remove arsenic at a temperature of 600-800℃. This can not only solve the problem of desulfurization and dearsenicization, but also convert the As2O3 produced during roasting into a powdery white arsenic product, which does not pollute the environment and can achieve the purpose of comprehensive utilization.
Bacterial oxidation of sulfide is a complex, bacterially catalyzed oxidation process that occurs at the mineral interface. Through bacterial oxidation of sulfides, minerals are desulfurized and dearsenicized, and crystals are destroyed, exposing the (ultra) fine gold wrapped in them, which is beneficial to the subsequent cyanide leaching of gold.
Common bacterial species for bacterial oxidation pretreatment include Thiobacillus ferrooxidans, Thiobacillus thiooxidans, and Microspirillum ferrooxidans. The chemical mechanisms of bacterial leaching mainly include direct action mechanism, indirect action mechanism, and composite action mechanism of bacteria.
During bacterial oxidation, arsenopyrite in arsenic gold ore is easily oxidized and decomposed, while realgar cannot be oxidized and decomposed by bacteria and will affect the activity of bacteria; during cyanidation leaching, arsenopyrite is very stable and does not undergo any side reactions, while realgar consumes cyanide and protective alkali, and the precipitate generated by the reaction forms a film on the surface of gold particles, hindering the cyanidation reaction of gold. Therefore, in the flotation enrichment operation of arsenic gold ore, realgar should be suppressed as much as possible.
For arsenic-containing difficult-to-treat gold ores, the current non-cyanide leaching process research is mainly leaching of thiosulfate and thiocyanate.
Thiosulfate leaching: An ammoniacal thiosulfate solution is used for leaching, which can effectively dissolve arsenic-containing minerals such as orpiment and realgar wrapped on the surface of gold particles, and gold can be effectively leached.
Thiocyanate leaching: is a type of halide containing -SCN. Compared with cyanide, it has the advantages of stable properties, low toxicity and low price.
The above is an introduction to the process of removing arsenic from arsenic-containing gold ore. In the actual gold extraction process, the arsenic characteristics and arsenic content of each gold ore are different, so the arsenic removal and gold extraction process methods used are also different. It is recommended to conduct mineral processing test analysis first and design a suitable arsenic-containing gold ore gold extraction process plan. At the same time, a set of gold extraction equipment can be regularly produced according to the process plan.
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