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Refractory gold ore refers to the ore that is difficult to extract gold directly through cyanidation leaching. This kind of gold ore usually needs to be pretreated and then leached to extract gold to obtain a better recovery rate. The commonly used pretreatment methods mainly include the following 6 types :
The roasting method is an earlier method used in the pretreatment of refractory gold ores. Usually, under high temperature conditions, air or oxygen-enriched roasting is used to decompose the sulfur and arsenic in the ore into SO2 and As2O3, so that the carbonaceous material is oxidized and deactivated. The loose and porous calcined sand is obtained, thereby exposing the gold in the ore, creating favorable conditions for the subsequent cyanidation gold leaching, and the produced SO2 and As2O3 can be comprehensively utilized through the flue gas recovery process.
The roasting method is especially suitable for refractory ores with sulfide-coated gold and carbonaceous "gold-robbing". According to different roasting conditions, it can be divided into oxidation roasting, calcium-added roasting, flash roasting, vacuum volatilization dearsenic roasting, microwave roasting and other methods.
Pressurized oxidation, also known as hot-pressed oxidation, is to add acid or alkali to oxidize and decompose arsenide and sulfide in refractory gold ore at a certain temperature (170-225°C) and pressure (total pressure 1-4MPa). A pretreatment method that exposes gold particles for subsequent cyanide leaching. In addition to the poor treatment effect on raw materials containing high organic carbon, the pressurized oxidation method has strong adaptability to various ores and concentrates, and has low sensitivity to material composition, regardless of the grade of sulfur and arsenic and harmful interference The process can adapt to the amount of impurity elements antimony and lead.
The method is a wet process with fast reaction speed and short pre-oxidation time. Through pressurized oxidation, the products after oxidation of pyrite and arsenopyrite are all soluble, the reaction is relatively thorough, and the recovery rate of gold is relatively high. High, the oxidation process does not produce flue gas pollution problems, and the waste residue produced exists in the form of relatively stable arsenate precipitation, with low environmental risk and an environmentally friendly process.
In order to significantly reduce the temperature and pressure of pressurized oxidation pretreatment, researchers have developed a nitric acid oxidation catalytic system, so that sulfide minerals can be rapidly oxidized and decomposed at lower temperatures and pressures.
Nitric acid is a strong oxidizing acid. Studies have shown that: under the condition of 75-85°C, use 150-200g/L nitric acid to decompose arsenic-containing flotation gold concentrate, and consume 100-300kg of nitric acid per ton of ore. Nitrate is denitrified at 350°C, and the consumption of nitric acid can be reduced by 1/2 to 2/3.
Oxygen is passed into the nitric acid medium or nitrate is used as a catalyst for air oxidation. The required conditions are temperature 100°C, pressure 400-800kPa, nitric acid is used as the carrier of oxygen to oxidize sulfide minerals, nitric acid is reduced to nitric oxide, and oxidized by oxygen Then it becomes nitric acid, which is equivalent to nitric acid as a catalyst, realizing the catalytic oxidation acid leaching of sulfide minerals.
When nitric acid catalytic oxidation is used for the pretreatment of arsenic-containing and sulfur-containing flotation gold concentrate, the process flow consists of five unit operations: pre-oxidation acid treatment, catalytic oxidation acid leaching, solid-liquid separation and washing, solution treatment and gold cyanide leaching composition.
The outstanding advantages of nitric acid oxidation pretreatment method are fast leaching speed (1-3h), air as oxidant, leaching agent (nitric acid) can be regenerated, and common structural materials such as stainless steel, polyvinyl chloride or glass steel can be used for reaction equipment.
The basic principle of alkali leaching pretreatment is to pre-inflate the alkaline pulp before cyanide leaching, so that some minerals that affect cyanide leaching, such as iron sulfide, arsenopyrite, stibnite and soluble sulfide, can be fully oxidized to reduce or eliminate Interference with the subsequent cyanidation process, for gold-bearing arsenopyrite minerals, alkaline leaching pretreatment oxidizes the surface to form arsenate compounds. Commonly used agents for alkaline leaching pretreatment include NaOH, KOH, Ca(OH)2 and ammonia water.
Chlorine oxidation method is an effective pretreatment method for carbonaceous refractory gold ore. It oxidizes carbon and organic compounds into carbon monoxide and carbon dioxide through chlorine gas, releases the wrapped fine gold particles, and eliminates the "robbing gold" effect of carbonaceous materials. The "robbing gold" effect of carbonaceous matter in fine-grained carbonaceous gold ore is mainly due to the fact that some cryptocrystalline graphite has a chemical structure similar to that of activated carbon for adsorbing gold. Chlorine or hypochlorite can oxidize the "robbing gold" functional groups on carbonaceous substances belonging to activated carbon and humic acid, or replace sulfur in organic carbon with chlorine, or combine on organic carbon in other ways, thereby passivating The adsorption of carbonaceous substances on gold cyanide complexes has been improved.
Bacterial oxidation pretreatment of arsenic-containing refractory gold ore is to use the ability of chemoautotrophic acidophilic microorganisms to oxidize sulfide ore, and sulfide minerals (such as arsenopyrite, pyrite, realgar, orpiment, marcasite) wrapped in fine gold particles , pyrrhotite, etc.) oxidative decomposition, so that the gold particles remain in the oxidized slag in a naked state, so as to facilitate more effective cyanidation or other methods of leaching gold, and also avoid harmful waste gas and other pretreatment processes. Disadvantages such as high energy consumption.
Bacterial oxidation is a complex process including chemical, electrochemical, and kinetic phenomena in the physiological growth of bacteria oxidizing Fe2+, elemental sulfur, etc., and the oxidation and decomposition of sulfide ores. It has both direct and indirect effects of bacteria.
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