Minimizing Arsenic Leaching from Water Treatment Process Residuals

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Ferric chloride addition was investigated for treatment of As-laden spent regeneration brine from ion exchange processes. Furthermore, varying conditions and calcium addition were investigated for the stabilization of the resulting As-laden solids. Arsenic, sulfate, bicarbonate, and chloride concentrations in the spent brine (300 mg/L, 605 mg/L, 305 mg/L, and 24 g/L, respectively) were orders of magnitude greater than typical drinking water treatment levels. Batch tests revealed that nearly 100% of the As in spent brine can be removed with a Fe/As molar ratio of 2 at circumneutral pH. The EPA TCLP and California WET tests were employed to determine the leachable As in the treatment residuals. When the brine was treated using a Fe/As molar ratio of 5 and 20, the resultant As-laden sludge easily passed the TCLP and WET respectively. Addition of calcium hydroxide (Ca(OH)2) in the Ca/Fe molar ratio 1.5 decreased leachable As by 80% in the WET. Calcium addition in an optimal range decreased the chemical costs by 18% and reduced the mass of sludge produced by 20%. To further investigate the impact of calcium addition, leaching tests were performed using a landfill leachate.

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