Efficiences and Mechanisms of Arsenic (As) Uptake from Aqueous Solution by Vivianite

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The provision of sustainable water resources of appropriate quality for various uses is one of the greatest and most important challenges facing society now and in the future. Within this context, demands on potable water are increasing as the human population grows and becomes more developed at a time when climate is changing the availability of water resources, and the quality of these resources is being undermined by overuse in many areas. Added to these is the problem that the quality of many large resources of water is compromised by natural contamination. For example, many anoxic lake, river and groundwater systems that provide the only sources of water for tens of millions of people worldwide are contaminated with arsenic (As). Consumption of these waters can lead to As toxicosis in animals, and to melanosis, gangrene, cancer and, ultimately, death in humans. Such a situation is best illustrated in West Bengal and Bangladesh, where, according to the World Health Organisation, there is the worst case of mass poisoning in the world. Obviously such a situation must not be allowed to continue if it is at all possible to remediate the problem. To this end, minerals may offer a solution if they are capable of uptaking and stabilizing potentially toxic elements such as As. The mineral vivianite [Fe3(PO4)2.8H2O] forms and is stable in these anoxic environments (acid mine drainage sites, rivers, lakes, urban water bodies), and initial experimental work shows that it can take up As, but its capacity for, and mechanisms of, uptake are not well understood. Our project will determine the efficiencies and mechanisms of uptake of As by vivianite so that it may be developed as a remediation tool in anoxic, As-contaminated water systems, thus protecting humans and ecosystems. This aim will be fulfilled by determining (1) the efficiency of sorption of As3+ and As5+ on synthetic vivianite by batch experiments, and (2) the mechanism of uptake of As3+ and As5+ on synthetic vivianite by spectroscopy. The project falls directly under NERC's priority area 'sustainable economies - identifying and providing sustainable solutions to the challenges associated with energy, land use and hazard mitigation'. The results of this study will be used by the large number of scientists and engineers worldwide studying the mechanisms of, and solutions to, As contamination of anoxic water systems, and, hopefully, offer a solution to the worst natural disaster facing society. The study will form the basis for further studies on synthetic and natural vivianite, including the influence of kinetics and bacteria on vivianite formation and As uptake.