Novel Adsorbent-Reactants for Treatment of Ash and Scrubber Pond Effluents

Abstract

The overall goal of this project was to evaluate the ability of novel adsorbent/reactants to remove specific toxic target chemicals from ash and scrubber pond effluents while producing stable residuals for ultimate disposal. The target chemicals studied were arsenic (As(III) and As(V)), mercury (Hg(II)) and selenium (Se(IV) and Se(VI)). The adsorbent/reactants that were evaluated are iron sulfide (FeS) and pyrite (FeS 2 ). Procedures for measuring concentrations of target compounds and characterizing the surfaces of adsorbent-reactants were developed. Effects of contact time, pH (7, 8, 9, 10) and sulfate concentration (0, 1, 10 mM) on removal of all target compounds on both adsorbent-reactants were determined. Stability tests were conducted to evaluate the extent to which target compounds were released from the adsorbent-reactants when pH changed. Surface characterization was conducted with x-ray photoelectron spectroscopy (XPS) to identify reactions occurring on the surface between the target compounds and surface iron and sulfur. Results indicated that target compounds could be removed by FeS 2 and FeS and that removal was affected by time, pH and surface reactions. Stability of residuals was generally good and appeared to be affected by the extent of surface reactions. Synthesized pyrite and mackinawite appear to have the required characteristics for removing the target compounds from wastewaters from ash ponds and scrubber ponds and producing stable residuals.

Sorption of selenium(IV) and selenium(VI) to mackinawite (FeS): Effect of contact time, extent of removal, sorption envelopes

“…In short, 0.1 M Na 2 S and 0.1 M FeCl 2 were initially mixed with equivalent volume ratio and then they were aged for 3 days. According to previous result, the synthesized FeS was identified to amorphous mackinawite [19]. The surface area of synthesized FeS was reported in literatures, ranging from 0.05 to 424 m 2 /g [22,23].…”

“…Previous research has demonstrated that mackinawite (FeS) can be a good reactant/adsorbent to remove selenium from water [19]. This study aims to provide fundamental information on the behavior of Se with adsorbent/reactant (FeS) as well as the basis for development of treating processes for ash and scrubber pond waters at coal-fired power plants that will be effective in removing Se and will produce residuals with low solubility.…”