生物炭复合材料对砷镉复合污染稻田的修复与机制研究

Farmland soil is always contaminated by more than one heavy metal especially As (metalloid) and Cd. However, rare studies have showed an effective remediation agent which can immobilize or detoxicate As and Cd in soils simultaneously, especially for flooded paddy soil-rice systems. Comparing with conventional remediation agents, biochar characterized by multiple benefits to environment and agriculture and especial high stability, is more suitable for flooded paddy soil-rice systems. .This project is designed to simultaneously reduce the accumulation in rice grain of As and Cd in contaminated paddy soil-rice systems. Remediation agents employed herein are biochar, Mg-modified biochar and Fe-modified biochar composites. Batch adsorption-desorption experiments, microcosm experiment for detection of volatile As and pot experiment are carried out to investigate: i) adsorption/precipitation mechanisms of toxic metal(loid)s including As(III), As(V) and Cd(II) on biochar-based composites in single- and multi-solute systems; ii) arsenic methylation and volatilization in soils influenced by biochar and the composites additions under submerged conditions and microbiological mechanisms; iii) speciation, mobility and phytoaccumulation of As and Cd in paddy soil-rice systems influenced by biochar-based composites treatments and potential mechanisms. ICP-MS-HPLC is used for species of As in soil solution and plants test, and XRD, FTIR, SEM-EDX, EXAFS, XANES for pre- and post-adsorption characterizations of adsorbents. .Simultaneous immobilization or detoxication of As and Cd in flooded paddy soil-rice systems is a highly important but difficult point so far. Thus, this project shows obvious innovation and practical significance.

本项目针对砷和镉复合污染稻田，应用生物炭及其负载铁、负载镁的生物炭复合材料为修复剂，围绕土壤-水稻系统中砷和镉的形态转化和迁移累积对添加修复剂的响应及机理开展研究。研究内容包括：1）生物炭复合材料对As(III)、As(V)和Cd(II)单一和共存条件下的吸附行为，通过XRD、FTIR、SEM-EDX、EXAFS、XANES等多种技术揭示吸附机理；2）微宇宙法捕获气态砷，重点研究添加生物炭及其复合材料对淹水土壤中砷的甲基化和挥发的影响与微生物学机制；3）盆栽试验研究添加生物炭复合材料对土壤-水稻系统中砷和镉的迁移转化和累积的影响与机制。.本项目可为同时减小污染土壤-水稻系统中砷和镉的迁移累积和毒性提供理论和实践基础，具有实际意义。

本项目针对砷和镉复合污染稻田，制备并优选出载镁稻秆炭并结合其他常用修复材料，围绕土壤-水稻系统中砷和镉的形态转化和迁移累积对添加修复剂的响应及机理开展研究。研究内容包括：1）用稻秆炭和载镁稻秆炭对水溶液中Cd(II)、As(V)和As(III)在单一和共存条件下进行吸附和解吸附试验，阐明吸附特征，运用XRD、FTIR、SEM-EDX等技术揭示吸附机理。2）通过砷挥发收集微宇宙模拟试验，阐明不同温度烧制的稻秆炭、载镁稻秆炭、稻秆和零价铁粉等对砷镉复合污染土壤中砷镉形态的变化与砷挥发的影响，并对砷氧化还原与砷甲基化功能基因（aioA、arrA、arsM）等进行高通量测序，探究土壤中砷功能微生物群落结构变化，揭示影响机制。3）盆栽全生育期种植水稻，探明不同修复材料对土壤-水稻系统中砷和镉的形态转化与迁移累积，分析影响水稻吸收和累积镉砷的机制。结果表明：1）载镁稻秆炭对溶液中镉的去除率达到99.8%，远远高于稻秆炭（20.9%）。载镁稻秆炭对Cd(II)、As(III)和As(V)的吸附量分别是稻秆炭的21.3、5.2和3.6倍。载镁稻秆炭主要通过沉淀作用、离子交换和络合反应吸附Cd(II)和As(V)，通过络合反应吸附As(III)。Cd(II)、As(III)、As(V)共存溶液中，载镁稻秆炭的吸附去除率远高于稻秆炭，两种炭材料均对As(III)有氧化作用。2）添加500℃烧制的稻秆炭和载镁炭后，总砷挥发量比对照分别显著减小38.5%和49.0%，添加稻秆大大增加了砷挥发量。总砷挥发量与土壤溶液中的As(III)呈显著正相关，土壤溶液中的As(III)浓度受DOC浓度的影响较大。各修复材料处理均改变了砷转化功能微生物(aioA、arrA、arsM)的群落结构，某些微生物丰度与土壤溶液中的各形态砷含量有显著相关关系。6）稻秆炭、载镁炭和铁粉处理中，水稻籽粒中的As(III)含量与对照相比分别显著减小42.2%、38.9%和32.5%，Cd含量与对照相比分别减小46.0%、91.0%和100%。. 稻秆炭、载镁炭和铁粉可以同时减小水稻籽粒中的镉和无机砷，对减小稻米中的镉砷含量与毒性有实际意义。不同修复材料影响下土壤中砷功能微生物群落结构与砷挥发的关系对调控或负载功能菌挥发去除土壤砷具有科学意义。