A new example of research on new technology of low potential bioleaching chalcopyrite

Hydrometallurgical process has been widely used in the processing of copper oxide ore and the secondary copper sulfide, copper resources but the body - chalcopyrite copper leaching rate is slow, the problem exists. To this end, hydrometallurgists have carried out extensive research to increase the rate of copper leaching in chalcopyrite. Studies have shown that adding an infusion is an effective way. For example, Ag ⁺ ions, a surface active agent, iron powder, activated carbon powder, but there are problems of high production or present.

In recent years, studies have reported that the presence of high concentrations of Fe2+ ions in acidic solutions contributes to the oxidative leaching of chalcopyrite by dissolved oxygen:

CuFeS ₂ +4H ⁺ +O ₂ =Cu ^{2 +} +Fe ^{2 +} +2S ⁰ +2H ₂ O (1)

The oxidative dissolution process of chalcopyrite releases Cu ^{2 +} and Fe ^{2 +} ions, forming a virtuous cycle and promoting the leaching of chalcopyrite. Therefore, the promotion of the dissolution of chalcopyrite by Fe ^{2 +} ions provides a possibility for wet processing of chalcopyrite. However, Fe ^{2 +} ions promote the acid consumption during the dissolution of chalcopyrite, and the reaction product sulfur covers the surface of the mineral, hindering the diffusion of metal ions and dissolved oxygen.

To this end, the use of sulfur oxidizing bacteria commonly used in biometallurgical processes to treat Fe ^{2 +} ions, to promote the dissolution of chalcopyrite products - monomeric sulfur. Using the strong oxidizing ability of sulfur-oxidizing bacteria to monomer sulfur, it is hoped that good results can be obtained in the following two aspects, and further enhance the promotion of Fe ^{2 +} ions on the dissolution of chalcopyrite: on the one hand, the monomer sulfur layer on the mineral surface is removed; On the one hand, it supplements the acid consumption of the chalcopyrite dissolution process.

First, the test materials and methods

(1) Preparation of mineral samples

The test ore sample is from the Dahongshan Copper Mine in Yunnan Province, and is processed by crushing, grinding, flotation and other processes to obtain chalcopyrite concentrate. The flotation concentrate uses 1mol/L HCLO ₄ solution to remove the floatation agent adsorbed by the mineral surface, such as xanthate, and then rinsed with deionized water. The nitrogen is dried under nitrogen at 25 °C. The use of Fourier transform infrared spectrometer to analyze the possible presence of the xanthate flotation agent in the mineral table to ensure the cleaning effect. The cleaned chalcopyrite concentrate was finely ground to -300 mesh using a vibratory mill for use in leaching tests. The chemical composition, content and particle size analysis results of the sample after fine grinding are shown in Table 1 and Table 2.

Table 1 Analysis results of chemical elements in mineral samples %

Table 2 Results of particle size analysis of mineral samples

(two) bacterial culture

The test strain is Acidithiobacillus thiooxidans, numbered Tetech-NTC-1; isolated and identified by laboratory, and currently deposited in the China Center for Type Culture Collection. The strain has high oxidative activity on monomeric sulfur. The medium used is (NH ₄ ) ₂ SO ₄ 3.0g/L, KCL 0.1g/L, MgSO ₄ •7H ₂ O 0.5 g/L, Ca(NO ₃ ) ₂ 0.01 g / L, K ₂ HPO ₄ 0.5 g / L, S powder 20.0 g / L, the optimum growth temperature of the bacteria is 30 ° C, can withstand pH range of 3.0 ~ 0.5. Figure 1 shows the change in pH of the culture medium and the rate of oxidation of the monomer sulfur during the growth of the bacteria.

Fig.1 Changes in pH and monomer sulfur oxidation rate during bacterial growth period

â–²-pH; â– -monosulfide oxidation rate

(3) Mineral leaching test

The low potential bioleaching test was carried out in a shake flask. Add 2.0g of chalcopyrite powder, 4.0g of FeSO ₄ •7H ₂ O, 150mL of Acidithiobacillus thiooxidans in a 300mL triangular conical flask; adjust the pH of the solution to 1.3 with H ₂ SO _{4 in the} initial stage of leaching, constant air bath vibration shaker Temperature 30 ° C, speed 175 r / min. The solution ORP is periodically tested, and the Cu content of the solution is sampled and the amount of water evaporation is supplemented. The leaching residue was filtered, vacuum dried, and the morphology of the leached slag was analyzed by X-ray and SEM theory.

The low potential chemical leaching test was essentially the same as the bioleaching test except that 150 mL of Acidithiobacillus thiooxidans was replaced with 150 mL of deionized water.

Second, the test results and discussion

(a) chemical and biological leaching processes

Figure 2 and Figure 3 show the effect of high concentration of Fe ^{2 +} ions on the oxidative dissolution of chalcopyrite in an acidic environment. Fe ^{2 +} ions effectively accelerate the reaction equation (1), Fe ^{2 +} acts like a catalyst "catalytic" in the process. Dissolution of chalcopyrite oxidation process continue to release Cu ^{2 +} ions and Fe2 ⁺ ions Fe ^{2 +} ions further consolidate the "catalysis." However, due to the presence of dissolved oxygen in the solution, part of the Fe ^{2 +} ions are oxidized to Fe ^{3 +} ions, see the reaction equation (2), changing the solution Fe ^{3 +} / Fe ^{2 +} ratio, and the solution oxidation-reduction potential increases. When the solution potential rises to a certain value, the chalcopyrite leaching rate drops rapidly. In addition, the chalcopyrite produced by the reaction formula (1), the product monomer sulfur covering the mineral surface hinders the diffusion of Fe ² +, Cu ^{2 +} ions and dissolved oxygen; while the concentration of Cu ² + ions in the solution is also increased for brass. Mineral dissolution produces an obstruction.

4Fe ^{2 +} +O ^{2 +} 4H ⁺ →4Fe ^{3 +} +2H ₂ O (2)

In order to accelerate the dissolution of chalcopyrite, reduce or eliminate the hindrance in the dissolution process of chalcopyrite, keep the low potential and low pH value (increasing the Fe ^{2 +} ion stability) during the process of Fe ^{2 +} ion promoting the oxidative dissolution of chalcopyrite Sexuality, reducing the rate of Fe ^{2 +} oxidation, and destroying the mineral surface product - monomeric sulfur, is an effective way to improve the leaching of chalcopyrite. It can be seen from Fig. 2 that the leaching rate of chalcopyrite is significantly improved after the addition of sulfur-oxidizing bacteria which can destroy the mineral surface reaction product-monomer sulfur.

Figure 2 Oxidative dissolution of chalcopyrite by high concentration of Fe ^{2 +} ions in an acidic environment

â—†-sterile; â– -bacteria

Temperature 30 ° C, Fe2+ 8g / L

Under conditions of low potential contrast chalcopyrite leaching process chemical and biological parameters of pH and ORP seen (FIG. 3): Add no effect on sulfur-oxidizing bacteria was almost ORP, i.e., the presence of sulfur oxidizing bacteria does not accelerate natural oxide Fe ^{2 +} Reaction (2). At the same time, the presence of sulfur-oxidizing bacteria oxidizes the reaction product of the chalcopyrite oxidation-monomer sulfur to form sulfuric acid, supplements the consumption of H ⁺ ions in the reaction equation (1), stabilizes the pH value of the solution, eliminates the inhibition of the sulfur layer on the mineral surface, and strengthens The leaching of chalcopyrite.

Figure 3 Relationship between pH value and ORP of chalcopyrite leaching solution in acidic environment

▲-sterile pH ●-bacteria ◆-pH value sterile ORP ■- sterile ORP

Temperature 30 ° C, Fe2+ 8g / L

(II) Leaching slag X-ray and SEM detection

From the reaction equation (1), it can be seen that the chalcopyrite is dissolved to form monomeric sulfur, and the X-ray pattern of the low-potential chemical leaching residue of the chalcopyrite in Fig. 4(a) shows the presence of a significant monomeric sulfur phase; The X-ray pattern of the low-potential bioleaching slag of chalcopyrite showed no significant monomeric sulfur image. This suggests that sulfur-oxidizing bacteria can be effectively utilized lysate chalcopyrite - elemental sulfur, preventing high concentration Fe ^{+ 2} under acidic conditions facilitate dissolution of chalcopyrite accumulation process.

Figure 4 X-ray map of low potential biochemical and chemical leaching slag in chalcopyrite

Figure 5 clearly shows the mineral morphology of chalcopyrite chemical or bioleaching slag under low potential conditions.

It can be seen from Fig. 5 that the chemical leaching residue has obvious erosion marks and sharp edges and corners; the energy spectrum micro-analysis also shows the presence of monomeric sulfur on the mineral surface. Relatively speaking, there is no obvious erosion mark on the bioleaching slag. The surface of the mineral is smooth and flat. The fine analysis reveals that some mineral particles adhere to the surface of the mineral. The energy spectrum analysis indicates that the crystal phase may be yellow iron vanadium ; for large particles and particles. The surface scan showed that there was no high sulfur content in the mineral surface.

In summary, the X-ray and SEM analysis of the leach residue further confirmed the high-efficiency sulfur oxidation performance of the sulfur-oxidizing bacteria, which can effectively utilize the chalcopyrite dissolution product-monomer sulfur.

Figure 5 SEM image of low potential biochemical and chemical leaching slag in chalcopyrite

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Third, the conclusion

(1) The presence of high concentration of Fe ^{2 +} ions under acidic conditions can effectively maintain the relatively low redox potential of the solution, maintain a reducing environment favorable for the dissolution of the first type of chalcopyrite in Dahongshan, Yunnan, and accelerate the dissolved oxygen and H ⁺ ions. Oxidative dissolution of chalcopyrite.

(2) The presence of sulfur-oxidizing bacteria does not oxidize Fe ^{2 +} ions, nor does it enhance the natural oxidation process of Fe ^{2 +} ions.

(3) It can make full use of the chalcopyrite oxidation dissolved product-monomer sulfur, supplement the acid consumption of the leaching process, maintain the low pH environment, destroy the possible sulfur layer, and promote the ion diffusion in the chalcopyrite dissolution process.

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