Sorption of mercury(II) to synthesized pyrite (FeS2) and stabilization via surface reaction
Chapter
Overview
Identity
Additional Document Info
View All
Overview
abstract
Mercury has been considered to be a global contaminant of significant concern for cuentries due to its high toxicity and bioaccumulation via the aquatic food chain, which seriously affects natural ecosystems and the health of humans. In this chapter, sorption of Hg(II) onto synthesized pyrite (FeS) was investigated by macroscopic, microscopic, and spectroscopic analysis techniques. Kinetics of removal of Hg(II) was very rapid at lower ratios of Hg(II)/pyrite. Concentrations of Hg(II) in solution were below detection limits within 10 minutes. A Hg(II)/pyrite ratio of 25 or greater was necessary to obtain measurable concentrations. This behavior indicates that the kinetics were similar to what would be expected if external transport controls. Maximum loadings of mercury typically exceeded 6 mmol/g and in some cases exceeded 20 mmol/g. These loading mean that the mass of mercury removed exceeded the mass of pyrite present. The pH of the solution did not appear to have a major effect on the extent of removal. However, there was a substantial amount of variability within the results of experiments at different pH. Exceptionally high removals of mercury could be the result of surface reactions and differences in removal could be the result of how fast these reactions occur at different pH. If experiments were conducted over longer time periods that would allow for initiation of surface reactions in all systems, then these differences would tend to decrease. Sulfate was observed to have little effect on removal of mercury by pyrite over the concentration range that was investigated (0-10 mM). X-ray photoelectron scopy (XPS) analysis of pyrite after contact with Hg(II) after 30 days showed evidence of Hg(II) reduction to Hg(I), coupled with oxidation of surface Fe(II) species, but no evidence of changes in oxidation state of surface sulfur was observed. Stability tests for mixtures of Hg and pyrite were conducted at two initial concentrations of Hg(II). Nearly complete removal (> 98%) was observed in all samples when the initial concentration was low. XPS analysis provided some evidence of mercury reduction and iron oxidation on the surface. When the initial concentration was high, low removal was observed at low pH, high removal at pH in the range pH 4-pH 6, and moderate removal at higher pH. Good stability was observed when pH was reduced. XPS analysis showed evidence of mercury reduction and good evidence of iron oxidation and formation of sulfur species that support formation of precipitates such as HgS or Hg2S. 2013 by Nova Science Publishers, Inc. All rights reserved.
