Low grade phosphate rock and bioleaching technology

Phosphorus is an important chemical raw material and an essential element for crop growth. Industrial phosphorus must be extracted from phosphate rock in large quantities. Although China's phosphate rock resources are abundant, the proven resource reserves are 13.24 billion tons, but the average grade is only 16.95%. (in terms of P ₂ O ₅ ), while the current industrial production of phosphoric acid requires phosphate rock containing P ₂ O ₅ ≥ 28%. Therefore, how to make full use of low-grade phosphate rock resources has become a strategic task with sustainable development.

With the rapid development of biotechnology, biological wet metallurgical industry, the use of low grade bacterial leaching of metal sulphide minerals it has been widely used, but is currently used for sulfide minerals leach gold, uranium, copper, or the like, and is applied to the leaching Phosphate rock is still relatively rare. Some organic heterotrophic bacteria, such as Rhizobium and Pseudomonas, can be grown by using organic substances such as glucose to produce organic acid-decomposing phosphate rock. However, the organic acid produced by the metabolism of heterotrophic bacteria is not strong, the decomposition of phosphate rock is slow, and organic nutrients need to be added as a carbon source for growth, so it is greatly limited in industrial applications. The inorganic autotrophic microorganism can directly fix CO ₂ as a carbon source from the air, and oxidize certain reduced inorganic substances (such as S ⁰ , FeS ₂ , Fe ^{2 +,} etc.) to obtain energy autotrophic growth, and produce inorganic strong acid. (such as H ₂ SO _{4 ,} etc.), the phosphate can be dissolved, which can reduce the cost and greatly accelerate the leaching speed. In this study, commonly used in the metallurgical industry biological inorganic autotrophic microorganisms - ferrous oxide leached acidophilic Thiobacillus (. Acidithiobacillus ferooxidans, At f) and eosinophils thiooxidans (Acidithiobacillus thiooxidans, At.t) Low Grade phosphate rock, which can use reduced sulfide or ferrous iron as an energy source to produce sulfuric acid to decompose phosphate rock. Acid and acid-induced breeding were carried out by ultraviolet irradiation and microwave physical mutagenesis. The original bacteria were used for leaching experiments, and the effect of adding Tween series surfactants on the leaching effect during the leaching process was studied.

First, the test method

(1) Strain preparation

Used in this test At. F and At. T is the sample from the acid mine water in a coal mine Anhui, enriched culture, separation, purification obtained bacterial culture medium components used in Table 1 to prepare a good proportion Table 1 After that, it was placed in an autoclave at 121 ° C and a pressure of 0.10 MPa for 30 min. The ferrous solution was sterilized by a 0.22 μm disposable needle. The ferrous solution and the sulfur powder were all proportioned when in use. Add the medium. The solid culture is a two-layer solid medium, the lower layer is a nutrient agar medium coated with red Drosophila, and the upper layer is a Starlcey or 9K solid medium coated with At. t or At. f, the nutrient composition of the medium and the corresponding The liquid medium is the same. The sulfur powder was replaced by 10% Na ₂ S ₂ O ₃ in an amount of 1 mL per 100 mL, using 2% agar as a coagulant. The medium components used for the two bacteria are shown in Table 1.

Table 1 Medium components used in two bacteria

(2) Violet induction test

After using a 15 W UV lamp, after preheating for 20 min, the bacteria solution was placed at a distance of 30 cm from the lamp, and the outside light was covered with a cloth, and irradiated for 1, 5, 10, and 15 min respectively. After the end of the irradiation, it was placed in the dark and refrigerated at 0 ° C for 1 h.

(3) Microwave induction test

Pipette a certain amount of bacteria in the logarithmic growth phase (about 3 days of culture), centrifuge at 1000 r/min for 10 min to remove the sulfur powder particles, and pipette the supernatant 10 mL into the culture dish and place the microwave oven (2 450). Mutagenesis was performed in MHz, 850 W) for a certain period of time. After the mutagenesis is completed, the plate is diluted and plated, and placed in a biochemical incubator for inversion culture.

(4) Phosphorus immersion test

The phosphate rock sample used in the test was taken from the Hubei Zhongxiang Phosphorus Mine. The original ore was crushed and ground to -200 mesh for the leaching test. The phosphate rock grade was 16.19%. Add 100 mL of medium to a 250 mL Erlenmeyer flask and inoculate 10% of the bacterial culture solution. In the surfactant test, a certain amount of Tween series surfactant should be added during the inoculation, and then 1 g of phosphate rock powder should be added. The mixture was shaken in a shaker (temperature 30 ° C, rotation speed 120 r / mm), the pH value of the solution was measured every day, and the evaporation amount of the liquid was supplemented with distilled water.

(5) Analytical test methods

A certain amount of phosphorus leaching supernatant solution, using potassium persulfate diluted after digestion - Sb Sepetrochrometry molybdenum (GB11893-89) several measurement P ₂ O ₅ content of the solution with 721 spectrophotometer. The pH of the solution during cultivation and leaching was measured using an Olilong 818 type acidity meter. Bacterial growth morphology and bacterial counts were observed using a Nikon CLPSE biomicroscope.

Second, the results and discussion

(1) Bacterial growth curve

Observation by light microscopy revealed that the cells were short rod-shaped or rod-shaped, and the individual bacteria were small, 0.5-1.0 μm wide and 1.0-2.0 μm long, and could swim in a single, opposite or short-chain longitudinal state. Semi-solid puncture culture showed that it was aerobic bacteria and Gram staining was negative. The pH value curves of At.t and Af. f bacteria during microwave mutagenesis were shown in Fig. 1 and Fig. 2. The pH curves of At.t and Af. f bacteria during UV mutagenesis were shown in Fig. 3 respectively. ,Figure 4.

Fig.1 pH curve of At.t bacteria during microwave mutagenesis

■-0S; ●-5S; ▲-10S; ▼-15S; t-30S; u-60S

Fig.2 pH curve of At.t bacteria during microwave mutagenesis

●-0S; ■-5S;®-10S; ▲-30S; ▼-60S

Fig.3 pH value curve of At.t bacteria during UV mutagenesis

®-0min; ▼-1min; ■-5min; ●-10min; ▲-15min

Fig.4 pH value curve of At.f bacteria during UV mutagenesis

-0min; ●-5min; ■-10min; ▲-10min

As can be seen from Fig. 1, Fig. 2, Fig. 3 and Fig. 4, the pH value will increase slightly in the first few days of culture. This is because the acid is consumed more in the early stage of the growth of the bacteria, and at this time the bacteria are just in the lag period and the acid production is not much; then it begins to decline. In general, the strains after mutagenesis mostly fall more than the pH of untreated strains. Under the same conditions, after 7 days of culture, the At. t bacteria were mutagenized by UV for 5 min, the pH value of the final bacterial solution could be reduced to 1.2, and the pH value of the bacterial solution on the 10th day of microwave mutagenesis could be lowered to 1.45; The effect of UV mutagenesis is not obvious, because the medium contains ferrous ions, and the color is deeper, which has a great shielding effect on ultraviolet rays. When the microwave is mutagenized for 10 s, the pH value of the bacteria solution can be reduced to below 2.0, and the effect can also be . When the UV irradiation time was 15 min or microwave treatment for 60 s, most of the bacteria were killed, so the pH of the bacterial solution did not change. The test results showed that the acid production ability of the bacteria after proper mutagenesis was enhanced.

(II) Leaching test results

During the process of bacteria leaching phosphate ore samples, the pH value of the system will also increase first. In addition to bacteria, phosphate rock will also consume a lot of acid. With the proliferation of bacteria, the pH value of the leaching system is continuously reduced, and the leaching is 15d. Basically, it tends to be stable in the future. In general, the leaching rate of bacteria to phosphate rock is increasing with the time of leaching. From the mechanism of bacterial leaching, it can be seen that the leaching of phosphorus is caused by the sulfuric acid produced by the sulfur in the oxidation state of the bacteria to leaching the phosphorus from the ore. Therefore, the most important factor affecting the phosphorus leaching is the pH value of the solution. It can be seen that the acid-producing ability of the mutagenized bacteria is greatly enhanced, and it can be seen that the leaching ability of the corresponding strains is also strong. Under the same experimental conditions, the leaching rate of phosphate rock by each strain after 20 days of leaching was shown in Table 2.

Table 2 Leaching rate of mutant strains after leaching of phosphate rock for 20 days

(3) The effect of surfactants

In order to improve the leaching rate and leaching effect of phosphate rock, several Tween surfactants (Tween 20, 60, 80) were added to Star-key and 9K medium, and their effects on the dosage and type were added. The test was carried out and the results are shown in Table 3.

Table 3 Leaching rate of strains after leaching of phosphate rock for 20 days after adding surfactant

The Tween series surfactant has a good effect on At. t bacteria, especially Tween 60, which can greatly increase the phosphorus leaching rate. The reason may be that the main nutrient substance S of At.t bacteria is hydrophobic on the surface, suspended in the liquid surface after adding the medium, and it takes several days to disperse in the medium, and the bacteria cannot be fully utilized; after the surfactant is added, the suspension is suspended. The elemental sulfur on the surface can be quickly dispersed in the solution, so that the bacteria can adhere to the surface of the sulfur powder, greatly improving the acid production effect, thereby improving the leaching effect. Conversely, for At. f, the effect of Tween is not very obvious, and in most cases it is not as good as adding surfactant, which may be because At. f is sensitive to the surface tension of the environment. According II M. Conoxcexxim other studies show that may reduce the surface tension of the medium could inhibit the growth of bacteria, when the medium to reduce the surface tension of 30 × 10 ^- When the ⁵ N / cm, some bacteria growth almost stopped.

Third, the conclusion

(1) Experiments using leaching phosphorus from At. t and At. f bacteria show that leaching of low-grade phosphate rock is completely feasible.

(B) using physical mutagenesis means acid-tolerant acid culture can improve the leaching rate, using UV to induce At. t bacteria for 5min can obtain better results; At.f bacteria using UV-induced effect is not obvious. The use of microwave-induced 10s breeding has a good effect on both Thiobacillus.

(3) Adding a surfactant can further improve the leaching effect, and for At.t bacteria, the effect of adding a surfactant is not obvious.