Evaluating Ferrous Chloride for Removal of Chromium From Ion-Exchange Waste Brines

摘要

Ferrous chloride (FeCl2) added to chromium-laden brines produced by strong base anion (SBA) exchange systems reduces hexavalent chromium (Cr(VI)) to trivalent chromium (Cr(III)) and precipitates the Cr(III) in a mixed chromium-iron hydroxide solid solution. A series of jar tests were conducted in which FeCl2 was added to synthetic SBA exchange brines. The variables investigated were the initial Cr(VI) concentration, initial pH, and ferrous iron stoichiometric dose. This reduction-coagulation-flocculation (RCF) process was also tested on field brines with various compositions. The RCF process achieved 77% chromium removal efficiency at all tested conditions, except in brines with a bicarbonate matrix. Significant vanadium (V) and arsenic (As) removal (78 and 49% removal, respectively) was observed in field brines with a chloride or sulfate matrix. Diffuse double-layer modeling suggests that adsorption to the precipitated solids was the predominant removal mechanism of V and As.