化学还原-生物刺激对高质量比Cr(Ⅵ)污染土壤治理及稳定化

Treatment and stabilization of high mass ratio hexavalent chromium contaminated soil by chemical reductants-biological stimulation

为提高Cr(Ⅵ)污染土壤治理后的稳定性,采用化学还原剂联合乙酸钠生物刺激对高质量比Cr(Ⅵ)污染土壤进行治理和稳定化。通过测定Cr(Ⅵ)质量比、Cr形态及含量并结合XRD分析,同时对生物刺激过程中Cr(Ⅵ)污染土壤的细菌多样性变化进行监测,对比多硫化钙(Calcium polysulfide,CPS)、硫酸亚铁(FeSO4)、零价铁3种化学还原剂以及乙酸钠用量对高质量比Cr(Ⅵ)污染土壤的治理能力及稳定化效果。结果表明:质量分数为10%的FeSO4与质量比为7 g/kg的乙酸钠联用,在生物刺激50 d时对高质量比Cr(Ⅵ)的去除及稳定化效果最佳,还原率为93.58%,且能够将毒性较大的生物有效态铬全部转化为其他稳定形态的铬。XRD结果表明,两种方法联用后土壤中Cr主要以Cr(Ⅲ)的形式存在。生物刺激过程中土壤细菌群落物种分布变化明显,生物刺激50 d时,富集的细菌类群最多。

To improve the stability of highly concentrated Cr(Ⅵ)contaminated soil after treatment,this paper used a chemical reducing agent combined with sodium acetate biostimulation to remediate high concentration Cr(Ⅵ)contaminated soil.By measuring Cr(Ⅵ)mass ratio,Cr speciation and content,XRD analysis,and monitoring the bacterial diversity of Cr(Ⅵ)contaminated soil during biostimulation,the reducing capacity and stabilization effect of three chemical reducing agents including calcium polysulfide,ferrous sulfate,zero-valent iron as well as the dosage of sodium acetate on high mass ratio Cr(Ⅵ)contaminated soil were compared.After extracting Cr(Ⅵ)in soil with an alkaline digestion solution prepared by 0.28 mol/L Na2 CO3/0.5 mol/L NaOH(pH>11.5),the concentration of Cr(Ⅵ)in soil was measured by 1,5-diphenylcarbazide spectrophotometry.Cr species and content were determined by ICP OES after extraction with a modified Tessier sequential extraction method.The results show that calcium polysulfide and ferrous sulfate have a good reduction effect on Cr(Ⅵ)in soil,while zero-valent iron has almost no effect.Compared with 2.15%calcium polysulfide,10.00%ferrous sulfate has a more important transformation effect on Cr(Ⅵ)speciation.10.00%ferrous sulfate combined with 7 g/kg sodium acetate has the best treatment and stabilization effect on high mass ratio of Cr(Ⅵ)when stimulated for 50 days,with a reduced rate of 93.58%,and all the more toxic bioavailable chromium can convert into other stable forms.Ferrous sulfate reduction and sodium acetate stabilization have little effect on soil pH.XRD analysis shows that Cr mainly exists in the form of Cr(Ⅲ)after treatment,and Cr is combined with soil crystals to achieve stable reduction.The bacterial diversity analysis shows that the distribution of soil microbial community species changes significantly during the biostimulation process.When biostimulated for 50 days,the enriched bacterial groups are the most.Bacillus sp.,which has been proven to have the ability of chromium reduction,is the dominant species in the process of biological stimulation and may participate in the treatment of Cr(Ⅵ).