Bacterial metallurgy technology due to its low cost and environmental protection friendly and become a hot research, especially for complex refractory ore conventional art (such as a single metal ore more compounds and multi-state metal composite mineral), low grade ore topsoil, Abandoned mines have unique advantages.

Isolated and purified from the culture described herein Liangzou Mineral Group -200 m mine water obtained Thiobacillus ferrous oxide, as bacterial leaching. The experiment was carried out by shake flask leaching, and activated carbon and Ag ⁺ , Tween and Ag ⁺ catalysts were added thereto.

First, experimental materials and instruments

The old tailings used in the experiment were taken from Liangzou Mining Group, and its chemical composition was (%) Cu 0.29, SiO ₂ 69.74, Al ₂ O ₃ 12.77, Fe ₂ O ₃ 3.19, CaO 2.36, MgO 1.35. The chemical phase of copper is: 5.41% of primary copper sulfide, 92.52% of secondary copper sulfide, 1.12% of free copper oxide, and 0.95% of copper sulfide. Tailings particle size distribution: -0.45mm~+0.200mm 14.37%, -0.200mm~+0.125mm 11.74%, -0.125 mm~+0.097mm 8.41%, -0.097mm~+0.074mm5.21%, -0.074mm 60.27 %.

The strain is a strain which is isolated from the acid mine pit water of Liangzou Mining and is domesticated and separated, and is mainly composed of Thiobacillus ferrooxidans. The medium was 9K+S medium: (NH ₄ )SO ₄ 3.0 g, KH ₂ PO ₄ 0.5 g, KCl 0.1 g, MgSO ₄ ·7H ₂ O 0.5 g, CaNO ₃ ·2H ₂ O 0.01 g, distilled water 700 mL, 1:1 H ₂ SO _{4 was} adjusted to pH = 2.0, sterilized at 121 ° C for 15 min, and 1% sulfur powder was added. The initial Fe ²⁺ concentration of the leachate was 1.0 g/L.

The experimental instruments mainly include PHS-3C precision acidity meter, controllable oscillation shaker, potentiometer, pH and Eh are measured by acidity meter, and Cu ²⁺ is measured by WFX-120 atomic absorption spectrophotometer.

Second, the experiment

(1) Test method

The sterilized medium was added to a 250 mL conical flask containing sterilized ore-containing powder, and the pH of the solution was adjusted with 1:1 H ₂ SO ₄ , and placed in a gas bath constant temperature shaking box at 30 ° C and a rotation speed of 150 r/min. In the middle leaching, the inoculation amount is 10%. 3.0mg / L Ag ⁺ as a catalyst, timed sampling, while monitoring the Cu ²⁺ , pH, Eh in the solution, using the medium to replenish the volume reduced by sampling in the solution to ensure that the total volume of the solution leaching does not change.

(II) Results and discussion

1. Effect of pH of leachate on leaching effect (Fig. 1)

Figure 1 Effect of pH on bacterial leaching

As can be seen from Figure 1, the acidity of the leachate has a great influence on the leaching of the bacteria, at pH = 1.5 to 2.0. The leaching effect is better. When pH=2.0, the leaching time of 25d leaching is the best. If the acidity is too high or too low, it will affect the survival and growth of bacteria and the breeding speed. When the pH is too high, the iron ions generated during bacterial leaching will be A brownish yellow precipitate (precipitate of iron hydroxide colloid) is formed, which covers the surface of the mineral ions, hinders the reaction from proceeding, and the pH is too low. Although the acidity is favorable for the oxidation of the ore, the bacteria are difficult to adapt to such high acidity, so that the bacteria The lag phase becomes longer, which affects the leaching effect of the bacteria. Therefore, the pH of the leachate is determined to be 2.0.

2. Effect of slurry concentration on copper leaching rate (Figure 2)

Figure 2 Effect of slurry concentration on copper leaching rate

Figure 2 shows that the concentration of the slurry is too large, but it is not good for leaching, because the accumulation of some metal ions in the solution may exceed the limit tolerance of the bacteria and affect the growth activity of the bacteria, and the concentration of bacteria in the leachate is certain. Under the increase of solid concentration, the collision and friction between the ore particles are intensified, which is beneficial to the continuous renewal of the mineral surface, but the number of bacteria per unit area of ​​the mineral is reduced, and the strong shear stress generated by the mineral surface is also adsorbed by the mineral surface. Bacterial damage and shedding, so that the bacteria adsorbed on the area of ​​the unit of minerals is reduced, resulting in a decrease in the leaching rate. Therefore, 10% of the pulp concentration is most suitable.

3. Effect of catalyst on copper leaching rate

Different amounts of activated carbon, Tween and Ag ^{+ were} combined as catalysts. The results of bacterial leaching of low grade beam Zou copper ore tailings are shown in Figures 3 to 4. Figure 3 shows that the leaching rate of 25d is 65% when no activated carbon is added, and the leaching rate increases with the increase of activated carbon. The more the amount of activated carbon, the better. The more activated carbon, the more bacteria adhere to the surface, which hinders the contact between bacteria and minerals and affects the leaching effect. When adding activated carbon to 0.3g, the leaching effect is better, 25d The leaching rate reached 92%. At the beginning of leaching, the bacteria are in the stage of adapting to the environment, and the old tailings contain low-grade arsenic , which has certain toxic effects on bacteria, but the concentration of arsenic in the leaching solution is low, so that the leaching speed of bacteria to minerals during the adaptation period Slower, the combination of activated carbon and Ag ⁺ copper leaching rate is higher than that of pure Ag ⁺ catalytic copper leaching. When leaching for 10 days, the catalytic effect of activated carbon is obviously improved, reaching 90% when the leaching time is 20d. As time goes on, the leaching rate hardly increases. With the increase of Fe ³⁺ , the mineral surface is covered with precipitates such as jarosite, which prevent the contact of bacteria with minerals, causing the leaching reaction to terminate and the copper leaching rate to no longer increase.

Figure 3 Effect of the amount of activated carbon on bacterial leaching

Figure 4 Effect of Tween dosage on bacterial leaching

It can be seen from Fig. 4 that the addition of Tween during leaching promotes the leaching and can shorten the "lag period" of the leaching. The Tween can change the wettability of the mineral surface, making it hydrophilic and susceptible to bacteria. Adsorption reduces the time required for bacteria to reach equilibrium on the mineral surface, thereby accelerating the rate of leaching, but the amount of Tween should not be too high, otherwise it is not good for leaching.

It can be seen from Fig. 5 that the leaching effect of the leaching of bacteria is better than that of the aseptic leaching. The combination of activated carbon and Ag ⁺ has better leaching effect than the combination of Tween and Ag ⁺ , and the leaching rate is 4 percentage points higher at 25 d.

Figure 5 Effect of catalyst on leaching

4. Effect of catalyst on leachate Eh

Most of the useful minerals in the mineral exist in the reduced state. The high oxidizing environment can promote the dissolution of the mineral in the dissolved state. It can be seen from Fig. 6 that the catalyst leaching is higher than the Eh which is not added, and the Eh change of the added catalyst is lower than that of the non-catalyst leaching solution. Obviously, the combination of activated carbon and Ag ⁺ is higher than the Eh of Tween 20 as a catalyst. It is indicated that in the process of leaching, the addition of Ag ⁺ can reduce the redox potential, and the presence of bacteria can maintain a relatively good oxidizing environment, which is beneficial to the leaching of Cu.

Figure 6 Effect of catalyst on solution Eb

Third, the conclusion

(1) When the pH of the leachate is 2.0 and the concentration of the pulp is 10%, Thiobacillus ferrooxidans has a good leaching effect on the old tailings;

(2) When the leaching temperature is 30 ° C and the rotation speed is 150 r / min, the bacteria are better than the bacteria-free leaching effect, and the leaching rate of the catalyst is higher than the pure Ag ⁺ leaching rate;

(3) 3.0g/L activated carbon and 3.0mg/L Ag ⁺ combination have better leaching effect than 3.0mL Tween and 3.0mg/L Ag ⁺ ;

(4) The potential of the leachate with catalyst is higher than the potential without addition.

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