Reliable techniques for synthesizing pyrite are necessary in order to develop effective treatment methods that use pyrite to remove arsenic from water and to stabilize arsenic in wastes. The Fe3+/HS- values of 0.500 and 0.571 at 60 degrees C and pH values ranging from 3.6 through 5.6 were found to produce pyrite most efficiently. Removal of As(V) was faster than removal of As(III) and the extent of removal of both As(III) and As(V) were more accurately described by the Langmuir adsorption model. Removal of As(III) was observed to increase as pH increased across the range investigated (pH 7-10). However, an optimum pH in the range between pH 8 and pH 9 was observed for removal of As(V). Sorption envelopes for As(III) showed low removal at low pH, increasing removal as pH was increased and moderate irreversibility as pH was titrated backward. Sorption envelopes for As(V) showed similar behavior except low removals were observed initially at high pH, removals increased as pH decreased and moderate to high levels of irreversibility were observed as pH was raised back to the initial values. (c) 2012 Elsevier Inc. All rights reserved.