I. Overview of microbial oxidation leaching
(1) Microbial leaching process
The process of microbial leaching is simple and easy to operate, and the leaching agent can act on the boundary area of ​​the grain. Therefore , the recovery rate of gold is high, generally more than 90% or even more than 95%, and the investment is small, does not pollute the environment, but the organism The oxidation reaction rate is slow, and the leaching time is long, generally 4 to 6 days. For the same processing capacity, the bacteria is oxidized, and the volume of the leaching equipment is large, so the power consumption of the agitator is also large.
(2) Mechanism of microbial oxidation of sulfide ore
Called microbial oxidation or bacterial oxidation process is based on certain bacteria (e.g., iron oxide thiooxidans) has the ability to turn the mineral sulfur and developed. Bacteria of pre-oxidized using Thiobacillus sp vulcanization mineral, mineral arsenide oxidative decomposition, destruction of the lattice, so that the wrapped metal sulfide minerals from these solutions out of favor after leaching, but also to achieve desulfurization The purpose of arsenic removal. Biological pre-oxidation is a promising and effective treatment method for pyrite and arsenic pyrite-type refractory gold ore.
The conditions of the presence of nutrients such as nitrogen, phosphorus and potassium in the acidic medium (pH 1-3), temperature (30 to 40 ° C, preferably 33 to 35 ° C), air (for O 2 , CO 2 ) Next, sulfur in sulfide, arsenide (pyrite, arsenopyrite, etc.) is oxidized to sulfuric acid (S 6+ ), iron is oxidized to high-sulfur sulfate (Fe 3+ ), arsenic is oxidized or arsenic acid (As 5 + ) Dissociate the wrapped gold.
(3) Principle flow chart of bioleaching method:
The principle flow of the bioleaching method is shown in Figure 1.
In the bioleaching, the iron, sulfur and arsenic of the sulfide are oxidized and dissolved, and soluble sulfuric acid, high-sulfur sulfate and arsenic acid, gold and silver are dissociated. At the same time, a part of the oxidized iron and arsenic precipitates with iron arsenate, yellow potassium iron, vanadium, etc., as the oxidation reaction progresses, the temperature of the slurry increases, so the serpentine tube in the tank passes cold water to maintain the temperature of 30-40 °C. At the same time, the pH of the slurry is lowered, and lime is added as needed to control the pH between 1.5 and 2.
(4) Treatment of leached products
The slurry after bioleaching is subjected to solid-liquid separation, which is generally concentrated and washed with a thickener. The bottom stream of the thickener contains gold, silver, unoxidized sulfide, gangue and a part of iron arsenate, jarosite, and silver samarium. After precipitation, the mixture was neutralized with lime to a pH of 10.5 and filtered to remove cyanide leaching.
Neutralization of concentrator overflow:
The bioleaching solution contains dissolved arsenic, iron, sulfur and a small amount of other metals, the most toxic of which is dissolved arsenic, which must be precipitated as a stable compound before being discharged together with the tailings. According to research, when there is an excess of Fe 3+ in the solution and Fe 3+ : As 5+ exceeds 3 to 3.5:1, and the pH is between 2 and 9, the arsenic precipitates with stable iron arsenate and no longer dissolves.
The concentrator overflows with limestone and lime to carry out two-stage neutralization and neutralization reaction to precipitate iron arsenic, sulfate and the like with gypsum , stable iron arsenate, jarosite and metal hydroxide. After the tailings are concentrated by the thickener, the underflow is discharged to the tailings dam, and the overflow can be recycled.
(V) The amount of 30t/d arsenic gold minerals Au30g/t, As6%±, technical indicators for biooxidation leaching and investment cost estimation
The production cycle is 4 to 6 days, the production cost is 380 yuan/t, the investment cost is 8.4 million, and the gold recovery rate is 90% to 95%.
Second, roasting cyanidation
(1) Roasting is an ancient and effective method for treating sulfur, arsenic, carbon refractory gold ore and concentrate
The purpose of roasting is to dissociate or expose the encapsulated gold in the form of microscopic and sub-fine particles from sulfide minerals and deuterated minerals, so that harmful impurities such as arsenic, sulfur and antimony are volatilized in the oxidation state to produce Porous calcine facilitates the contact of cyanide leachate with gold to increase the recovery of gold, which is oxidized or passivated during calcination and loses activity.
The calcination is carried out in a calciner having a boiling furnace, a multi-hearth furnace and a rotary kiln. Boiling furnaces are commonly used to treat pre-oxidative roasting of large quantities of pyrite, arsenopyrite and telluride concentrates.
(2) Main chemical reactions during roasting
1. Calcination of gold in gold concentrate
Au 2 Te+O 2 =2Au+TeO 2
2. Calcination of carbonaceous ore
C+O 2 =CO 2 ↑
3. Oxidation roasting of sulfur concentrate
Calcination reaction of pyrite
Pyrite roasting temperature is generally between 500 and 750 ° C
Hematite is formed by the following reaction when pyrite is calcined in a roaster with a strong oxidizing atmosphere (excess air).
4FeS 2 +11O 2 =2Fe 2 O 3 +8SO 2
When the pyrite is calcined in a weakly oxidizing atmosphere (restricted air feed), black magnetite ore is produced.
3FeS 2 +8O 2 =Fe 3 O 4 +6SO 2
4. Arsenic gold ore and fine mineral roasting
For the treatment of arsenic-containing ore, usually two-stage roasting is carried out. The first-stage roasting is carried out at a lower temperature (generally 450-575 ° C) and insufficient oxygen content to remove arsenic, and arsenic is removed by volatilization of arsenic trioxide. Cool, collect and sell.
Calcination produces low arsenic calcine, which is mainly composed of magnetite, and its reaction is:
12FeAsS+29O 2 =4Fe 3 O 4 +6As 2 O 3 +12SO 2
3FeS+SO 2 =Fe 3 O 4 +6SO 2
2As 2 S 3 +9O 2 =2As 2 O 3 +6SO 2
Most of the residual arsenic in the calcine is various iron arsenate.
Fe 2 O 3 +As 2 O 3 +O 2 =2FeASO 4
The reaction does not proceed too much in the first stage because Fe 2 O 3 is produced very little. If the temperature exceeds 500 ° C in this stage, the As 2 O 3 vapor pressure can reach 1 atm, and part of As 2 O 3 is due to the furnace oxidant ( The action of Fe 2 O 3 , SO 2 , etc., which is easily reducible in the air, is converted into As 2 O 5 with low volatility, and elevated temperature and an excessively strong oxidizing atmosphere promote the formation of As 2 O 5 . When a metal oxide is present in the charge, the resulting As 2 O 5 will react with the metal oxide (CaO, CuO, FeO, PbO) to form an arsenate.
As 2 O 3 +O 2 =As 2 O 5
As 2 O 5 +3CaO=Ca 3 (AsO4) 2
As 2 O 5 +3FeO=Fe 3 (AsO4) 2
As 2 O 5 +2PbO=Pb 2 (AsO4) 2
The produced arsenate is very stable, and arsenate is the main state of residual arsenic in the calcine, and this peroxidation of arsenic is disadvantageous to cyanidation.
In order to improve the arsenic removal rate, it is necessary to control the calcination temperature, the oxygen content in the furnace, the furnace gas discharge rate and other factors, and even a small amount of reducing agent (such as carbon powder) can be added to promote the conversion of As 2 O 5 (pentavalent arsenic) into As. 2 O 3 (trivalent arsenic) is volatilized to reduce the arsenic content in the calcine.
The second stage is calcined at a higher temperature (generally 600-700 ° C) and excess oxygen, the main purpose is to completely decompose the pyrite, so that the sulfur is further removed in the form of SO 2 , which is mainly composed of magnetite. The calcine is oxidized to hematite.
The main reactions are as follows:
2FeS 2 +11O 2 =2Fe 2 O 3 +8SO 2
4Fe 3 O 4 +O 2 =6Fe 2 O 3
FeAsS+3O 2 =FeAsO 4 +SO 2
Under strong oxidizing atmosphere, the iron arsenate produced by roasting of arsenic pyrite is unfavorable for cyanidation. When FeNaO 4 is cyanide immersion gold, the extraction of gold is inhibited. The ideal calcination is 70%-80%. The hematite and the dark brown calcine of 20% to 30% of the magnetite, the gold cyanide leaching rate is higher.
Sulfide and carbon are exothermic in the calcination process. If the concentrate contains 18% to 20% sulfide sulfur and is fed with a slurry containing about 70% solids, the calcination can be autothermally burned without the need for fuel.
Arsenic ore or concentrate often contains various gangue minerals such as quartz , calcite , dolomite, magnesite , gypsum, etc. The following reactions occur during roasting:
The above-mentioned MgO and CaO reacted with SO 2 in the furnace gas to form CaSO 4 or MgSO 4 to reduce the SO 2 content in the furnace gas, but the formation of CaSO 4 inhibits gold extraction when cyanidation gold is immersed.
(III) Purification of As 2 O 3 steam
Typically, the As 2 O 3 vapor is condensed into a solid powder, As 2 O 3 (white crucible), by a dust removal system.
(4) Treatment with SO 2 fumes
When the flotation concentrate is naturally calcined, the sulfur content is high, so the concentration of SO 2 in the flue gas is relatively high, and it is generally used for producing sulfuric acid.
In the whole dust removal system, the negative pressure operation must be maintained to keep the furnace gas discharged at a certain speed. If the exhaust speed is too fast, the fine gold in the material will be extracted from the kiln together with As 2 O 3 and SO 2 , thus Caused the loss of gold.
(5) Advantages and disadvantages of the roasting process
1. Advantages: The process is simple and mature. When the ore contains a certain amount of sulfur or carbon, the roasting process can be carried out spontaneously. The SO 2 in the furnace gas can be recovered in the form of sulfuric acid, and the arsenic can be white arsenic (As 2 O 3 ). Form recovery, calcination pretreatment is the best and economical process solution.
2. Disadvantages: Flue gas containing sulfur, arsenic, antimony and mercury pollutes the environment. To meet the national emission standards, it must be purified to increase the cost of pollution control. It is not costly to achieve self-heating ore or concentrate for roasting.
In addition, the effect of calcination and high-pressure oxidation on ores or concentrates containing high silver is not as good as that of bacteria or chemical oxidation. This is due to the formation of low-melting sulfides or ferrites during calcination to encapsulate gold, resulting in cyanidation of silver. The leaching rate is reduced.
When the ore contains carbon and other base metals (such as copper , cobalt , nickel , zinc ), pyrite roasting is difficult because carbon oxidation requires higher temperatures (>650 ° C), but copper, cobalt, nickel Sulfides such as zinc react to form low-melting sulfides or ferrites. Gold (especially silver) is encapsulated in ferrite to reduce the cyanide leaching rate of gold and silver, at lower temperatures (<600 ° C). Incomplete oxidation of the lower calcination (especially organic matter) will lead to the adsorption of gold and silver by carbonaceous materials. Therefore, such carbonaceous ores are not suitable for oxidation and are usually pretreated by chemical oxidation or pressure oxidation.
(6) The recovery rate of cyanidation and gold extraction from roasting pretreatment is about 85% to 90%. The production cost is equivalent to the biological oxidation pretreatment, and the investment cost should be budgeted.
Third, the process of enrichment of reconcentration of concentrate containing high arsenic
Generally, the arsenic-bearing gold ore gold has a very fine particle size and is wrapped in pyrite or arsenopyrite. Therefore, it is less likely to use re-flotation to enrich gold. To improve the grade of gold, The method of separating the mixed concentrates is used to increase the gold grade of the gold concentrate.
Specific application of separation methods available lime or air oxidation and soft manganese ore and potassium permanganate method for inhibiting separation of pyrite, but care must be taken not too much amount of the oxidizing agent, the oxidizing agent should not be too long contact time with the pulp, or It will activate arsenopyrite. The gold arsenic-pyrite concentrate of a certain plant in China contains 180.74g/t of gold and 8.3% of arsenic. The mine uses potassium permanganate to test the inhibition of arsenic pyrite. The specific test conditions are as follows: It is 15%, the potassium permanganate dosage is 100g/t, the (original ore) agent is in contact with the slurry for 5 minutes, and the butyl xanthate is 80g/t, and the golden iron ore is floated. The test results are as follows. The gold-pyrite concentrate contains 328.05g/t of gold, 1.74% of arsenic, and the gold recovery rate is 93.43%, while the arsenic concentrate contains 24.5g/t of gold and 15.26% of arsenic. The rate is 89.22%.
Fourth, the conclusion
For Au fine powder Au 30g / t, As 6% is to use biooxidation pretreatment, cyanide gold extraction, or to use roasting oxidation to pretreat gold, or to use separation flotation to improve the grade of gold concentrate, which should be tested The comparison between technical indicators and economic indicators is preferred.
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