Arsenic contamination in drinking water is the cause of serious health problems in some underdeveloped areas of the world such as Southeast Asia, and can also cause long-term health effects in the developed world. At low concentrations arsenic is poisonous, and in many countries drinking water exceeds the allowed maximum contaminant level (MCL) of 10 µg/L (10 ppb), which is the level set by the EPA and the World Health Organization (WHO). The most common sources of arsenic contamination include natural geological sources, mining operations, insecticides, weed killers, wood preservatives, and somewhat in the electronics industry. Calcite has been proposed as a remediation solution; this mineral is the main constituent of limestone. Limestone is relatively cheap and arsenic has been shown to readily adsorb onto it. However, the logistics of the removal of the arsenic-contaminated calcite, and many other issues, have yet to be resolved.

Arsenic speciation is very important to consider when determining toxicity and remediation of the contamination. For example, arsenite, As(III), is more toxic than arsenate, As(V). Depending on the environmental conditions, both oxidation states of arsenic can come in a variety of protonated forms that could affect its reactivity and fate in solution.

This summer, my project will focus on the adsorption of both As(III) and As(V) onto calcite. I will be varying the conditions such as pH, concentration of arsenic, and use of either a model groundwater solution or a pre-equilibrated solution. Analytic methods may include X-ray diffraction, X-ray fluorescence, directly-coupled plasma spectrophotometry, and EXAFS at Brookhaven’s National Synchrotron Light Source.
References:
David J. Vaughan. Arsenic, Elements, 2, 2, (2006) 71-75.