Vink Jos P M, van Zomeren Andre, Dijkstra Joris J, Comans Rob N J
Deltares, Unit Subsurface & Groundwater Systems, PO-box 85467, 3508 AL Utrecht, The Netherlands.
Energy Research Centre of the Netherlands, PO-box 1, 1755 ZG Petten, The Netherlands.
Environ Pollut. 2017 Aug;227:146-156. doi: 10.1016/j.envpol.2017.04.016. Epub 2017 Apr 28.
Simulating the storage of aerobic soils under water, the chemical speciation of heavy metals and arsenic was studied over a long-term reduction period. Time-dynamic and redox-discrete measurements in reactors were used to study geochemical changes. Large kinetic differences in the net-complexation quantities of heavy metals with sulfides was observed, and elevated pore water concentrations remained for a prolonged period (>1 year) specifically for As, B, Ba, Co, Mo, and Ni. Arsenic is associated to the iron phases as a co-precipitate or sorbed fraction to Fe-(hydr)oxides, and it is being released into solution as a consequence of the reduction of iron. The composition of dissolved organic matter (DOM) in reducing pore water was monitored, and relative contributions of fulvic, humic and hydrophylic compounds were measured via analytical batch procedures. Quantitative and qualitative shifts in organic compounds occur during reduction; DOM increased up to a factor 10, while fulvic acids become dominant over humic acids which disappear altogether as reduction progresses. Both the hydrophobic and hydrophilic fractions increase and may even become the dominant fraction. Reactive amorphous and crystalline iron phases, as well as dissolved FeII/FeIII speciation, were measured and used as input for the geochemical model to improve predictions for risk assessment to suboxic and anaerobic environments. The release of arsenic is related to readily reducible iron fractions that may be identified by 1 mM CaCl extraction procedure. Including DOM concentration shifts and compositional changes during reduction significantly improved model simulations, enabling the prediction of peak concentrations and identification of soils with increased emission risk. Practical methods are suggested to facilitate the practice of environmentally acceptable soil storage under water.
通过模拟好氧土壤在水下的储存情况，研究了重金属和砷在长期还原期内的化学形态。利用反应器中的时间动态和氧化还原离散测量来研究地球化学变化。观察到重金属与硫化物的净络合量存在较大的动力学差异，特别是对于砷、硼、钡、钴、钼和镍，孔隙水中的浓度在较长时间（>1年）内一直保持升高。砷作为共沉淀或吸附在铁（氢）氧化物上的部分与铁相相关联，并由于铁的还原而释放到溶液中。监测了还原孔隙水中溶解有机物（DOM）的组成，并通过分析批次程序测量了富里酸、腐殖酸和亲水性化合物的相对贡献量。在还原过程中有机化合物会发生定量和定性的变化；DOM增加了10倍，随着还原的进行，富里酸变得比腐殖酸占主导地位甚至腐殖酸完全消失。疏水和亲水部分都增加，甚至可能成为主要部分。测量了活性无定形和结晶铁相以及溶解的FeII/FeIII形态，并将其用作地球化学模型的输入，以改进对缺氧和厌氧环境风险评估的预测能力。砷的释放与易还原铁部分有关，这可以通过1 mM CaCl提取程序来识别。纳入还原过程中DOM浓度变化和组成变化显著改善了模型模拟，能够预测峰值浓度并识别具有增加排放风险的土壤。建议采用实际方法来促进水下环境可接受的土壤储存实践。
