生物炭对含As(Ⅲ)水铁矿还原过程中砷形态及矿物转化的影响

Effects of biochar on the arsenic and mineral transformation in the reduction process of As(Ⅲ)-adsorbed ferrihydrite

生物炭的施用对土壤铁(氢)氧化物还原、砷(As)的形态转化有重要作用,极大地影响了As的环境行为.本文研究了生物炭/AQDS(蒽醌⁃2,6⁃二磺酸盐)对含As(Ⅲ)水铁矿化学还原和异化还原的影响,探索了由此产生的非生物和生物过程中Fe和As的形态转化及次生矿物的形成.结果表明,生物炭和AQDS的添加可以促进水铁矿的化学还原和As(Ⅲ)的化学氧化,AQDS促进水铁矿化学还原和As释放的能力强,生物炭促进As形态转化的能力强;生物组在添加Shewanellaoneidensis MR⁃1后发现,生物炭和AQDS的添加可以促进Fe(Ⅱ)的生成,AQDS的添加促进Fe(Ⅱ)的生成、As形态转化和释放的能力要高于生物炭.EEM结果表明,生物炭产生的DOM可以与溶液中的物质发生氧化还原作用从而被消耗.循环伏安曲线在0.25V处观察到一个小而宽的阳极峰(B),可能对应了As(Ⅲ)氧化为As(V).XRD结果显示AQDS处理的非生物组和生物组出现了蓝铁矿,表明AQDS可以促进次生矿物的生成.EDX⁃SEM结果表明,新矿物的生成有利于As的固定(BCF:0.73%<BF:1.69%<BAF:1.82%).通过穆斯堡尔谱拟合,得到AQDS处理非生物组和生物组蓝铁矿的相对含量分别为13.1%和26.3%.本研究有助于理解生物炭和铁还原菌对As和Fe地球化学循环的影响,为降低土壤As有效性和毒性、降低As污染环境风险提供了理论依据.

Biochar plays an important role in the reduction of iron(hydr)oxide and the transformation of arsenic(As)in soils,greatly affects the environmental behavior of As.The effects of biochar and anthraquinone-2,6-disulphonate(AQDS)on the process of As(Ⅲ)-adsorbed ferrihydrite chemical and microbial reduction were studied.The behavior of Fe and As and the production of secondary minerals in the abiotic and biological processes were explored.Results showed that the addition of biochar and AQDS can promote the chemical reduction of ferrihydrite and the chemical oxidation of As(Ⅲ).AQDS has a strong ability to facilitate the chemical reduction of ferrihydrite as well as the release of As,and biochar has a strong ability to promote the speciation transformation of As.During the microbial reduction,biochar and AQDS can promote the reduction of iron mineral,while AQDS has the stronger ability to promote Fe(Ⅱ)generaion,As speciation transformation and As release than biochar.EEM results showed that DOM produced by biochar could be consumed by redox reaction with substances in solutions.Cyclic voltammetry(CV)result showed that a small and wide anodic peak(B)was observed at 0.25 V,possibly corresponding to the oxidation of As(Ⅲ)to As(V).XRD results showed that vivianite was produced only in AQDS treatment under abiotic and biological conditions,indicating that AQDS can promote the generation of secondary minerals.The mapping of As indicated that As could be adsorbed on the vivianite or incorporated into the vivianite structure to reduce its amount released(BCF:0.73%<BF:1.69%<BAF:1.82%).The M9 ssbauer results showed that the relative contents of vivianite in AQDS treatment under abiotic and biological conditions were 13.1%and 26.3%,respectively.The study is important for a better understanding of the effects of biochar and iron-reducing bacteria on the geochemical cycles of As and Fe,providing a theoretical basis for reducing the availability and toxicity of As in soils and the environmental risk of As pollution.