Arsenic removal and stabilization by synthesized pyrite

Arsenic is ubiquitous whether it is naturally occurring or produced by humans. It is found at sites on the National Priority List and at sites operated by DOE, where it is the second most commonly found contaminant. More wastes containing arsenic will be produced due to the lowering of the Maximum Contaminant Level (MCL) for arsenic in drinking water which will result in more treatment facilities for arsenic removal that will generate residuals. Furthermore, arsenic can be released from such wastes under the reduced conditions that are found in landfills. Pyrite (FeS2) is believed to be a compound that has a high affinity for arsenic and is stable under anoxic conditions. The first task of this research was to develop a method for making pyrite crystals of defined size with minimal reaction time and at high yield. Effects on the synthesis of pyrite particles of pH, the ratio of Fe/S, temperature and reaction time were investigated in batch reactor systems. Pyrite was synthesized within 24 hours at pH values ranging from pH 3.6 through pH 5.6, and at a ratio of Fe/S of 0.5. X-ray diffraction and scanning electron microscopy were used to size and characterize the pyrite particles. Experimental and analytical procedures developed for this work, included a hydride generation atomic absorption spectrometry method for measuring arsenic species (As(III), As(V)). The synthesized pyrite was applied to remove arsenic and its maximum capacity for arsenic removal was measured in batch adsorption experiments to be 3.23 μmol/g for As(III) and 113 μmol/g for As(V). Information obtained on the characteristics of chemical species before and after the reaction with arsenic showed that iron and sulfur were oxidized. Last, how strongly arsenic was bound to pyrite was investigated and it was determined that release of arsenic from As(III)-pyrite is not affected by pH, but release from As(V)-pyrite is affected by pH with minimum release in the range pH 5 to pH 8