地下水系统中硫氧化还原循环对砷迁移转化的影响研究

The Datong Basin is a typical area where groundwater contains high concentrations of sulfur and arsenic in China. The sulfur is undergoing or/and has undergone intensive (bio-)redox cycling within aquifer systems in this area. The field monitoring, simulation experiments, thermodynamic computation and reactive-transport modeling will be jointly conducted in this project to quantitatively discuss the effects of (bio-)redox cycling of sulfur on arsenic mobilization and enrichment in groundwater from the Datong Basin. The groundwater flow model of the Datong field experimental plot will be set up with MODFLOW according to our previous hydrogeological survey and monitoring results. Groundwater arsenic and sulfur speciation, arsenic thioanions, and arsenic-bearing iron minerals will be quantified through on-site and laboratory analyses. Thermodynamic modeling computation will be performed using PHREEQC to identify the pathways of sulfur redox transformations and their mediation in primary geochemical processes controlling arsenic mobilization in groundwater. Arsenic geochemical cycling under sulfidic condition will be developed by combining the results of batch experiments with thermodynamic computation. And then, a coupled steady-state reactive-transport model will be formulated and calibrated using PHT3D to help unravel the pathways and quantify the effects of sulfur redox transformations on arsenic mobilization within groundwater aquifer systems of the Datong Basin. The study can provide consolidated scientific support for a full understanding the genesis of high arsenic groundwater.

大同盆地是我国典型高砷地下水分布区，含水层系统中硫经历了强烈的（生物）氧化还原循环。项目拟选取大同盆地高砷地下水野外试验场为研究区，采用野外监测、模拟实验、热力学计算与反应-迁移耦合模拟相结合的方法，定量探讨硫（生物）氧化还原循环对地下水系统中砷迁移转化的影响。首先，基于场地水文地质条件、前期调查与监测数据，建立场地高砷含水层系统地下水流模型。然后，通过对地下水中砷形态、硫形态、（多）硫代砷化合物组成及砷赋存铁矿物相的精确测定与模拟计算，准确识别地下水系统中硫（生物）氧化还原循环途径及其诱导下砷迁移转化的主导性地球化学过程。在此基础上，建立富硫环境中砷的地球化学循环模型。最后，通过整合水流模型和砷的地球化学循环模型，实现砷的反应-迁移耦合模拟计算，定量刻画硫（生物）氧化还原循环对砷迁移富集的影响机制。研究对揭示高砷地下水形成机理具有重要意义，有望进一步丰富和完善高砷地下水成因理论体系。

项目针对地下水系统中砷的赋存形态、硫酸盐还原促进砷释放的机理研究方面取得了新进展。研究发现强还原、碱性、富硫环境下硫代砷化合物的形成是地下水中砷富集的关键水文地球化学过程，提出了硫（生物）地球化学循环形成硫代砷化合物控制砷迁移富集这一新机制。通过模型定量刻画了地下水水化学与水文地质条件对砷原位固定的影响。研究成果为区域劣质地下水改良提供了新思路，对推动了地下水污染修复技术进步，对保障高砷地下水分布区供水安全具有重要的理论与实践指导意义。依托项目发表高水平学术论文19篇，授权国家专利3项；培养博士研究生4人，硕士研究生15人；开展国际合作与交流7人次。