Preliminary studies on mercury solubility in the presence of iron oxide phases using static headspace analysis

Abstract

Discharge of elemental mercury caused by certain industrial activities has been a leading cause of mercury contamination of natural aquatic systems. Although elemental mercury has a relatively low solubility in water, even such low concentrations may lead to unacceptable levels of contamination, depending on, among other factors, the potential of elemental mercury to oxidize and form ionic species, which generally have much higher solubility. A laboratory study was conducted to investigate the solubility of mercury in the presence of amphoteric oxides of iron, an electron acceptor. Investigations were performed with and without chloride in solution, a rather ubiquitous component of mercury wastes. Mercury was analyzed using a relatively fast and inexpensive technique, the static headspace method, and the results were selectively compared with those obtained using a more laborious and expensive, but conventional, United States Environmental Protection Agency-approved atomic absorption method. Mercury solubility decreased in the presence of iron oxides, suggesting adsorption of mercury ions at the oxide-water interface. There was indirect evidence of oxidation of elemental mercury to ionic species in the presence of free iron in solution. Mercury solubility generally increased in the presence of chloride in solution because of the formation of weakly adsorbing mercury-chloro complexes. The precision and accuracy of the static headspace method of mercury analysis were acceptable for a field-screening tool.