Study On Bioremediation Of Lead Pollution In Phosphate Mining Wasteland

The reserves of phosphate rock are very rich in China,however,most of them are mid-low-grade phosphate rock(PR),which leads to the serious phenomenon of“mined rich and abandoned poor”in the mining process,resulting in a large number of phosphate mining wastelands.There is a certain degree of heavy metal pollution,especially lead(Pb)pollution in phosphate mining wastelands.If the Pb pollution can not be remediated in time,it will continuously accumulate in the soil,and it will affect the surrounding environment after being washed by rainwater and migration of elements.At present,seldom studies focused on the bioremediation of phosphate mining wasteland Pb pollution.Therefore,this study concentrated on removal of Pb pollution in phosphate mining wasteland by phosphate-solubilizing bacterium(PSB)and microbial-plant combination.The relevant research is carried out with the following aspects.The results were expected to provide a certain scientific theoretical basis and technical support for solving the scientific problem of Pb pollution in China's phosphate mining wasteland.1.A PSB with high Pb tolerance was isolated from a phosphate mining wasteland named LA.Based on its cell morphology,physiology,and phylogenetic analysis,it was identified as Pseudomonas sp.2.The phosphate solubilization and Pb tolereance capabilities of strain LA were studied in this study.The results indicated that LA could effectively solubilize tricalcium phosphate and release soluble phosphate in PKO culture medium.The concentration of soluble phosphate reached higest 637 mg/L at the fifth day.Moreover,strain LA has strong abilities to tolerate Pb and remove Pb ion pollution effectively.When starch,fructose and sucrose were used as the sole carbon source,the removal rate of Pb ions by LA was 95.41%,98.50%and 88.8.%,respectively.And when peptone was used as the sole nitrogen source,the removal rate of Pb ions was 94.87%.3.PR solubilization and the potential of Pb immobilization were investigated at this study.The results demonstrated that soluble phosphate was highly effective in immobilizing Pb,which was directly related to the medium p H value.With the concentration of Pb increased,the concentration of soluble phosphate in the medium decreased and the p H increased gradually at the same time.Compared with the blank control,the removal rate of Pb enhanced significantly.When the initial concentration of Pb²⁺was 100 mg/L,the immobilization rate of Pb was enhanced from 80.48%to 97.46%.4.Further,the mechanisms underlying solubilization of PR and biomineralization of Pb ions in LA were evaluated by Fourier transform infrared spectroscopy(FT-IR)and X-ray(XRD)diffraction.The results showed that some functional groups on the PR surface and LA were altered,and LA could form hydroxyapatite and pyrophosphate with Pb ions.5.In this study,the combined remediation effect of applying Pb-tolerant PSB LA and two indigenous plants on Pb-contaminated soil were studied through pot experiments.The indigenous plants ryegrass and sonchus which grow in phosphate mining wasteland were selected as the test plants,the simulated Pb pollution in two forms of Pb nitrate(Pb(NO₃)₂)and Pb carbonate(Pb CO₃)were mainly experimental objects.The results showed when the strain LA were inoculated to the Pb contaminated phosphate mining wasteland soil,the plants growth was effectively promoted,the available phosphate content in the soil along with the concentration of phosphate in plants increased,and the bioavailable Pb in the soil was decreased.Moreover,when strain LA were inoculated to the soil contaminated with Pb CO₃,the insoluble Pb in the soil can be solubilized and transformed into ionic by strain LA so that can be absorbed by plants and combined with soluble phosphate,one part of which was absorbed and accumulated by plants,the other part was immobilized in the soil and conver to be more stable Pb-phosphate compounds with soluble phosphate released by insoluble phosphate solubilizing,thereby realize the bioremediation of Pb pollution in phosphate mining wastelands.