Leaching of high-arsenic copper concentrate by combination of medium and high temperature leaching bacteria
High Arsenic copper concentrates mainly refers to more than 2% of arsenic in copper concentrate. Copper and arsenic separation is a major problem in the field of metallurgy. At present, the research on arsenic removal by bacteria at home and abroad mainly focuses on high arsenic gold concentrate. There are few studies on bacterial leaching of high arsenic copper concentrate. The copper concentrate mainly composed of arsenic bismuth copper ore has a high arsenic content, the arsenic-copper ratio is generally 1:3 to 5, and the arsenic content in the copper concentrate can be as high as 6% to 8%. The arsenic-bearing ore samples studied in this experiment are mainly arsenic-copper-copper ore. Wen Huan et al. conducted a mid-temperature leaching leaching test on a flotation concentrate of arsenic-containing low-grade copper sulfide ore in China. The copper mineral of the flotation concentrate is mainly secondary copper sulfide ore, and a very small amount of chalcopyrite. And porphyrite, the main arsenic-containing mineral is sulfur arsenic copper ore, As 0.79%, Cu 17.98%, copper leaching rate can reach 85.52%. Zhou Wei et al. conducted a medium-temperature leaching leaching test on a high-arsenic copper sulfide concentrate in a copper mine in Yunnan. The concentrate contains 2.5% arsenic, 11.48% copper, and 62.3% copper. The raw copper sulfide ore accounts for 35.7% of the total copper content, the leaching time is 10 days, and the copper leaching rate is 30%. It can be seen from the above experiments that the medium-temperature leaching bacteria have better leaching effect on the high-arsenic copper concentrate mainly composed of secondary copper sulfide ore and the high-arsenic copper concentrate mainly composed of primary copper sulfide ore.
In the past 20 years, a large number of studies have been carried out on the bacterial leaching of primary copper sulfide ore. Studies have shown that the leaching rate of thermophilic acidophilic bacteria (also known as high temperature bacteria) to the original copper sulfide ore is several times (more than 5 times) the medium temperature leaching bacteria. Foreign studies on the bioleaching of thermophilic acidophilic bacteria in chalcopyrite concentrates have been carried out abroad. For example, BacT ech/MinTech Tasmania mine in Australia uses medium thermophilic acidophilic bacteria to leach chalcopyrite concentrate at a temperature of 48 ° C, a treatment capacity of 5 kg / d, and a copper leaching rate of 96.4%. The Kunming Institute of Metallurgy in China also completed the study of leaching low-grade chalcopyrite with thermophilic acidophilic bacteria and achieved breakthrough results. Strictly mineralized autotrophic thermophilic acidophilic bacteria were isolated from water samples collected from a hot spring area in Yunnan, and used for bioleaching of low-grade copper sulfide ore, mainly chalcopyrite, with medium-temperature Thiobacillus In comparison, under the same test conditions (except for the leaching temperature), the leaching rate of the total copper by the thermophilic acidophilic bacteria reached 97%, which was three times that of the medium temperature leaching bacteria leaching rate of 32.43%. Based on the residual chalcopyrite in the leaching residue, the leaching rate of the thermophilic acidophilic bacteria to chalcopyrite is 97.05%, which is 6 times that of the medium temperature leaching bacteria leaching rate of 15.43%. The thermophilic acidophilic bacteria have special effects on the leaching of chalcopyrite, but no research reports on high arsenic copper concentrate have been reported. This paper focuses on the bioleaching of high-arsenic copper concentrates by thermophilic acidophiles.
One and two-stage leaching test principle
According to the physiological and biochemical characteristics of each of the medium temperature Thiobacillus and thermophilic acidophilus, the two-stage leaching method was used to treat the high arsenic copper concentrate. The first paragraph: on the one hand the use of medium temperature Thiobacillus (optimal growth temperature: about 30 ° C) has a strong tolerance to arsenic, in the high arsenic environment can play a strong oxidative leaching effect, leaching copper concentrate Most of the arsenic, at this time arsenic is mainly present as As 3+ . Further oxidation converts As 3+ to As 5+ , adjusts the pH appropriately, and As 5+ reacts with excess Fe 3+ in the leachate to form a stable precipitate of iron arsenate ( scorodite), thereby reducing the arsenic content in the leachate to reduce Toxicity to the second stage of high temperature bacteria; on the other hand, the use of medium temperature leaching bacteria has strong oxidative leaching ability to secondary copper sulfide ore, and leachable high arsenic copper concentrate. The second paragraph: the use of high temperature leaching bacteria (optimal growth temperature: 65 ° C) for the leaching of the refractory primary copper sulfide ore strong leaching ability, in a relatively short period of time to make most of the refractory primary copper sulfide ore leaching , Cu 2+ enters the solution. Solid-liquid separation can remove arsenic.
Second, test materials and methods
(1) Mineral samples and strains
Test ore sample: obtained from a flotation beneficiation plant Yunnan copper concentrate, copper and multi-element chemical phase analysis results shown in Table 1, Table 2.
Table 1 Chemical multi-element analysis of high arsenic copper concentrate (mass fraction) /%
1) As content of copper concentrate varies with different batches of ore samples, the range of change is 3.0% to 8.0%. The components listed in the above table are the test samples. If the arsenic content is high or lower than the above table, then The method of blending is used to stabilize it at about 4.39%; 2) the unit is g/t.
Table 2 Analysis of copper phase of high arsenic copper concentrate
As can be seen from Table 2, the copper concentrate is an oxygen-sulfur mixed ore with an oxidation rate close to 50%. The copper sulfide ore is dominated by primary copper sulfide ore. X-ray diffraction analysis shows that the primary copper sulfide ore is mainly arsenic-copper-bearing ore, about 60% to 70%, and the chalcopyrite is about 30% to 40%.
Test strains: high-arsenic-resistant medium-temperature leaching bacteria and high-temperature leaching bacteria selected by long-term laboratory acclimation, screening and mutagenesis.
(two) analysis and detection methods
Phase analysis: Phase analysis before and after leaching of mineral bacteria by X-ray diffractometer, Japan Shimadzu EPMA-1600 electron probe and the like.
Chemical elemental analysis: Determination of copper, soluble iron ions (Fe 2+ and Fe 3+) concentration using a weight of chromium potassium titration or atomic absorption spectrometry Method iodine.
pH measurement: using a precision pH meter or precision pH test paper.
(3) Stirring leaching test method
Weigh a few ore powder, add the medium in a ratio of 1:10 (w / v), adjust the pH to about 2.0 with a 1: 1 sulfuric acid solution, wait until the pH value is stable, then add the bacteria solution at a 10% ratio, weigh the weight Stirring leaching experiments were carried out in a water bath at 30 ° C (medium temperature leaching bacteria) or 65 ° C (high temperature leaching bacteria). A sterile acid immersion control plus 0.2% mercuric sulfate. During the leaching process, the pH value is controlled between 1.5 and 2.0, and the evaporating water is added to the fixed weight with a suitable temperature tap water three times a day. The supernatant is taken at regular intervals to analyze the copper, iron, etc. entering the solution. The leaching period is 10d. The sampling amount was supplemented with basic medium, and after the test, the mixture was filtered. The leaching residue was washed with 1% dilute hydrochloric acid for several times, and then dried and weighed. The content and phase of residual copper and arsenic in the leaching residue were analyzed.
Third, the test results and discussion
(1) Effect of medium or high temperature leaching bacteria alone or in combination on leaching effect
The leaching rate of the high-temperature leaching bacteria to the primary copper sulfide ore-chalcopyrite is faster and the leaching rate is higher. The leaching effect of high temperature bacteria on primary copper sulfide ore dominated by arsenic bismuth copper ore has not been reported. In this experiment, different leaching strains or combinations thereof were used at different times of the leaching cycle to study the oxidative leaching characteristics of the high arsenic copper concentrates by the application of the medium temperature bacteria and the high temperature bacteria respectively.
Establish a high temperature bacteria group, a medium temperature group and a medium temperature group. High temperature bacteria group: high temperature leaching bacteria were used in the whole leaching period (10 days); medium and high temperature bacteria group leaching in one or two stages: medium temperature bacteria in the early stage of leaching test (1~6d) and high temperature bacteria in late stage (7~10d); Medium temperature bacteria group: medium temperature leaching bacteria were used throughout the leaching period (10d). The leaching results are shown in Figure 1.
Fig.1 Effect of different leaching strains on leaching effect in different leaching periods
It can be seen from Fig. 1 that the two-stage leaching is the use of medium-temperature leaching bacteria in the early stage of the test, and the medium-high temperature bacteria group using high-temperature leaching bacteria in the later stage has the highest copper leaching rate. The leaching period uses only high-temperature leaching bacteria or only medium-temperature leaching bacteria, and the leaching effect of the two is not as good as that of the medium-high temperature leaching bacteria leached by the two-stage method. The two-stage combination of bacteria was leached for 10 days, the total copper leaching rate was 90.01%, while the medium temperature bacteria group was 78.13%, and the high temperature bacteria group was 55.16%. Only with medium temperature bacteria, the total copper leaching rate of leaching for 6d reached 70%, then the leaching rate increased slowly, and the leaching time continued to increase to 10d. The leaching rate still showed no significant increase, only increased by 8.13%. However, in the later stage of the leaching of the two-stage leaching slag, the total copper leaching rate increased to about 20% after being transferred to the high-temperature leaching system. The X-ray diffraction analysis was carried out on the leaching residue of the medium temperature bacteria group. The copper minerals in the slag were mainly arsenic bismuth copper ore, followed by chalcopyrite, and the medium temperature leaching bacteria to the original copper sulphide ore such as arsenic bismuth copper ore and chalcopyrite. The leaching effect was poor, the copper leaching rates were 17.48% and 14.2%, respectively, and the total leaching rate for the primary copper sulfide ore was 16.26%. as shown in Table 3.
Table 3 Analysis of primary sulfide copper mineral phase of leaching residue/%
From the X-ray diffraction analysis results of the high temperature bacteria leaching in Table 3, it is known that the arsenic bismuth copper ore and a very small amount of chalcopyrite remain in the slag, but the content of the two is much less than that before the high temperature bacteria leaching. It indicated that the high temperature bacteria had strong oxidative leaching ability to the primary copper sulfide ore such as arsenic bismuth copper ore and chalcopyrite in the late stage of two-stage leaching. The leaching rate of high temperature bacteria to chalcopyrite was 78.45%, which was medium temperature leaching. The leaching rate of arsenic bismuth copper ore is 33.42%, which is about 2 times of 17.48% of medium temperature leaching bacteria; the total leaching rate of primary copper sulphide ore is 50.24%, which is about medium temperature immersion. The mineral bacteria is 3 times as much as 16.26%. However, the oxidative leaching effect of high temperature bacteria on arsenic bismuth copper ore is worse than that of chalcopyrite. It can be seen from Fig. 1 that the tempering period of bacterial growth is longer than that of the high temperature bacteria leached by the high temperature bacteria, and the leaching rate and leaching rate are far less than those of the medium temperature group and the medium temperature group. It is indicated that the leaching system of the high temperature bacteria group is not conducive to its strong oxidative leaching effect from the beginning. High arsenic in the pulp may be one of the inhibitors of the growth and reproduction of high temperature bacteria and the efficient activity of oxidation. Electron probe analysis shows that arsenic in the leaching residue mainly exists in the form of iron arsenate.
According to the data, As 3+ ions are only present in concentrated acid solution. Since biooxidation is carried out in a relatively acidic environment (pH 1.5 to 2.0), the generation and presence of As 3+ is unavoidable in the biooxidation of arsenic. In biooxidation, different bacteria have different tolerance to arsenic. It has been suggested that the growth of medium-temperature leaching bacteria such as Thiobacillus ferrooxidans and Thiobacillus thiooxidans under the conditions of 5g/L arsenite and 40g/L arsenate is inhibited. When the concentration of As 3+ in the solution is 30 mmol/L (2.55 g/L), it is the main source of toxicity for medium thermophilic bacteria. The tolerance of moderate temperature bacteria to As 3+ is higher than that of warm bacteria. The results of this test also confirm this point on the one hand, because under the same test conditions, the total copper leaching rate of the high temperature bacteria group is much lower than that of the medium temperature bacteria group.
(B) the effect of the addition of Fe 3+ on bacterial leaching
It can be seen from the above studies that As 3+ and As 5+ are highly toxic to medium and high temperature leaching bacteria, As 3+ inhibits bacteria much more than As 5+ , and high temperature bacteria on As 3+ and As 5+ The tolerance is worse than that of the medium temperature leaching bacteria. The study found that in the process of biooxidation, arsenic first enters the solution in the state of As 3+ , and it is very stable in the process of biooxidation, and it needs a strong oxidant to oxidize it to As 5+ . Therefore, in order to reduce the toxicity of As 3+ to bacteria, especially the two-stage leaching of high-temperature leaching bacteria in the biooxidation process, it is necessary to accelerate the oxidation of As 3+ → As 5+ , and the As 5+ and the Fe 3+ in the leachate. The reaction produces iron arsenate precipitated into the slag. According to research, in the biooxidation process, Fe 3+ , Fe / As molar ratio, etc., will affect the oxidation of As 3 + .
Fe 3+ is an oxidizing agent and has a strong oxidizing property. Under certain conditions, Fe 3+ can oxidize As 3+ in the leachate to As 5+ . Only As 5+ can react with Fe 3+ in solution to form iron arsenate precipitate. The reaction equation is as follows:
In the middle-temperature leaching system in the early stage of two-stage leaching, the effect of Fe 3+ on the leaching of high-arsenic copper concentrate by medium-temperature leaching bacteria was studied by adding different concentrations of Fe 3+ . 3+ added amount.
In three test groups of medium temperature leaching system were added 2.0,7.5,15g / L of Fe 3+, is added in the form of (SO 4) 3 of the Fe 2; establishment of the control group without addition of Fe 3+. 2.0 g/L Fe 3+ addition amount calculation basis: in the leachate without added Fe 3+ {(Fe 3+ +Fe 2+ )+added Fe 3+ } molar concentration As( As 3+ +As 5+ Molar concentration = 3 to 6. The test results are shown in Figure 2.
Fig. 2 Effect of the addition amount of Fe 3+ on the leaching of medium temperature leaching bacteria
It can be seen from Fig. 2 that the addition of Fe 3+ in the medium temperature leaching system can accelerate the leaching rate of the medium temperature leaching bacteria. However, the higher the concentration of Fe 3+ added, the lower the bacterial leaching rate. Tests have shown that the addition amount of 2.0 g/L of Fe 3+ is optimal. The higher the concentration of Fe 3+ in the leaching system, the lower the leaching rate is still unclear.
(III) Effect of the addition of pyrite concentrate on bacterial leaching
In the biological oxidation leachate, the arsenic ions mainly form iron arsenate (FeAsO 4 ) precipitate, so the excess Fe 3+ in the solution is the main condition for the precipitation reaction. In the leachate, the concentration of various ions (Fe 2+ , Fe 3+ , As 3+ , As 5+ ) varies depending on the oxidation rate of various minerals, and the influence on the formation of iron arsenate is also large. In order to ensure the complete precipitation of arsenic ions, the molar ratio of Fe/As in the solution is generally 3 to 6. Adding Fe 3+ results from the influence of mesophilic bioleaching bacteria leaching found, adding an appropriate amount of leaching solution to Fe 3+ mesophilic bioleaching leaching rate indeed promoted. However, considering the cost of production, adding a large amount in the leaching system is not realistic Fe 3+, when using bacterial oxidation of pyrite leaching can generate Fe 2+, Fe 3+ characteristics by adding pyrite added to Fe 3+, In order to achieve the purpose of excess Fe 3+ in the leachate.
The following experiments mainly investigated the effect of adding pyrite on the leaching of medium-temperature leaching bacteria in the medium-temperature leaching system and the optimum addition amount of pyrite.
The test is divided into two steps: 1 preparation of the pyrite concentrate culture solution. The experimental group was inoculated with 10% (w/v) medium temperature leaching bacteria in 2.5%, 5.0% (w/v) pyrite concentrate 600 mL slurry, and stirred for 7 days in a 30 °C water bath. 2 medium temperature leaching bacteria leaching test. 60 g of high arsenic copper concentrate test ore sample was added to each bacterial culture solution, and the leaching test was started. The control group did not add the pyrite concentrate bacterial culture solution. The test results are shown in Figure 3.
It can be seen from Fig. 3 that adding a certain amount of pyrite concentrate can improve the leaching rate of the medium temperature leaching bacteria, because the pyrite concentrate culture medium contains a large amount of Fe 3+ and Fe 2+ , which can supplement the leaching system. Need Fe 3+ . The amount of pyrite concentrate added is 2.5%.
Fig. 3 Effect of adding pyrite concentrate on leaching of medium temperature leaching bacteria
Fourth, the conclusion
(1) The leaching rate and the high leaching rate of the high-temperature leaching bacteria combined with the two-stage leaching method can reach a high leaching rate of 90. 01%. The analysis of the primary copper sulfide mineral phase of the leaching residue shows that the leaching rate of the high temperature bacteria to the chalcopyrite is up to 78.45%, which is more than 5.5 times that of the intermediate temperature leaching bacteria 14.2%; The leaching rate is 33.42%, which is about twice that of 17.48% of the medium temperature leaching bacteria; the total leaching rate of the original copper sulphide ore is 50.24%, which is three times that of the middle temperature leaching bacteria 16.26%. However, the oxidative leaching effect of high temperature bacteria on arsenic bismuth copper ore is worse than that of chalcopyrite; the two-stage method is suitable for high-efficiency bioleaching of high arsenic copper concentrate, which can ensure the high temperature bacteria to arsenic bismuth copper ore to a certain extent. The primary copper sulfide ore such as copper ore exerts a strong oxidative leaching effect. Although the medium temperature leaching bacteria have higher oxidative leaching ability to the primary copper sulphide ore, the temperature leaching bacteria are poor, but the tolerance to As 3+ and As 5+ is higher than that of the warm bacteria. The two-stage method is the use of medium-temperature bacteria in the early stage of leaching, which utilizes the characteristics of moderate temperature bacteria to have strong tolerance to arsenic, and at the same time leaching easily leached sulfide ore; the use of high temperature bacteria in the late leaching period utilizes high temperature bacteria to have original copper sulfide ore. Strong leaching characteristics. The combination of the two will be the focus of future biometallurgical research and industrialization.
(2) Adding proper amount of Fe 3+ or pyrite concentrate in the early stage of two-stage leaching can accelerate the leaching rate of medium-temperature leaching bacteria. The former is the best with 2.0 g/LFe 3+ , and the latter is 2.5. The amount of % added is sufficient, but it is added in the form of a bacterial culture solution.
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