Unexpected Precipitation Observed during Arsenic Removal from Water via Sorbent Modified with a Mixed Oxidation State Manganese

摘要

Drinking water contamination with As(V) is a crucial problem for millions of people dependent on groundwater resources in some regions of the world. Accumulation of arsenic compounds in the body by using such water poses serious health risks. Among many types of materials, Mn-modified sorbents are used for water treatment and arsenic removal. In this short communication, a newly observed phenomenon is reported, being an unexpected precipitation process occurring during the As(V) sorption from an aqueous solution via Mn-modified clinoptilolite. The quantity of formed precipitates was observed to increase with the initial concentration of As(V) present in water. While this short communication is intended only to report a novel observation, some implications can be expected. Additional studies are required to understand the underlying mechanism and implications of such precipitation during the water treatment process, raising questions on limitations of the use of such sorbents. While it is not completely certain, limited experimental evidence indicates that precipitates are formed by interaction of Mn8010CI3 (mixed oxidation state Mn) and As(V), and exist in the form of hydrates. The precipitates are unstable in air at room temperature and moderate humidity, and degrade shortly thereafter outside of water solution.