Combined Regulation Of Fraction Distribution And Phytoavailability Of Soil Lead By Emendment With Sulfur-iron Modified Biochar And Thiobacillus

Industrial activities,including mining,primary and secondary smelting,manufacturing of lead batteries,and lead pigments,are caused series Pb pollution.Soil lead pollution is one of the serious environmental issues around the world.The Pb in soil is easy transferred into food chain,and finally damage human health due to the high toxicity,bioaccumulation and non-degradability.Phytoremediation is an in-situ,effective,economical,and environment friendly method for soil remediation.However,phytoremediation is limited with the mobility of Pb in soil.In this study,the mixed microorganisms from high sulfur coal were collected for phytoremediation.The iron-sulfur modified biochar was prepared from sawdust,and used for enrichement of Thiobacillus.The effect of modified biochar and mixed microorganisms on Pb-contaminated soil was investigated with soil culture experiments.The mechanisms of biochar and mixed microorganisms on phytoremediation were investigated with ryegrass pot experiments.In this study,the mixed microorganisms were collected from a high sulfur coal,Sulfobacillus?7.47%?and Thiobacillus?11.11%?were dominant bacteria of the mixed microorganisms on genus level.The pyrite in coal was oxidized to H₂SO₄ and Fe₂?SO₄?₃ by mixed microorganisms.The microbial enrichement leads to the decrease of p H,increases of oxidation-reduction potential?ORP?,and the release of Fe³⁺.According to the metabolic characteristics of mixed microorganisms,sulfur-iron modified biochar was prepared as microbial carrier.The biochar named Fe SC550 was prepared with loading pyrrhotite(Fe_1-xS)and magnetite in sawdust biochar.The mixed microorganisms growth for 36 d in together with bio-oxidization of pyrrhotite decreased the Fe SC550 system p H from 4.32 to 3.50,the ORP increased from 298 to487 m V,the Ca²⁺and Fe³⁺release reached 0.56 mg/g and 25.48 mg/g.The XRD spectra showed that the pyrrhotite was oxidized and the jarosite was generated during the microbial enrichment.The FT-IR spectra indicate that microorganisms were adsorbed on Fe SC550 through surface functional groups.The Fe SC550 was analyzed with Raman spectra,pore structure analysis and SEM-EDS,the results showed that the catalytic effect of iron promotes the development of pyrolysis and pore structure of Fe SC550,which is benefited to the adsorption and enrichment of mixed microorganisms on the surface of biochar.A 60-day of soil culture experiments were carried out with mixed microorganisms and Fe SC550.After 60 days of Fe SC550 addition in Pb-contaminated soil,Thiobacillus is becoming the dominant microorganism on genus level,and the abundance increased from 0.06%to 34.55%.The addition of mixed microorganisms could increase the abundance of Thiobacillus,Marmoricola,and Lysobacter in soil.Both Marmoricola and Lysobacter can increase plant resistance to insects and disease.The acid extractable fraction of Pb in soil increased by 73.01%with addition of Fe SC550 and mixed microorganisms after the soil culture experiments.Fe SC550 can decrease the Eh of soil,which lead the release of Pb from the reducible fraction in soil.With the microbial oxidizen of Fe SC550,the Fe³⁺and H⁺were generate,the soil p H decreased and the Eh increased.The changes of p H and Eh lead to the release of Pb from reducible fraction and oxidizable fractions.The soil organic carbon was increased with the addition of Fe SC550 caused the increase of oxidizable fractions in soil,as well as the adsorption and adsorb of Thiobacillus on Pb.The jarosite formation by biomineralization may increase the residual fraction of Pb in soil.The effect of Fe SC550 and Thiobacillus on Pb bioavailability was investigated with a 60-day pot experiments.Thiobacillus is become the dominant microorganism on genus level with the addition of Fe SC550 in soil.The bioavailability of Pb in soil was significantly increased with the addition of Fe SC550 and mixed microorganisms.The amount of Pb in ryegrass was increased by 69.54%and 203.20%in highly polluted?995 mg/kg?and low polluted soils?203 mg/kg?.The small molecule organic acid secreted by the root system of ryegrass and the oxidation of Thiobacillus on pyrrhotite promote the absorption of lead by plants.