(319c) Crystallization of Low Solubility Calcium-Arsenate Compounds for Arsenic Removal from Poly(Diallyldimethyl Ammonium Chloride)-Arsenate Solution

Arsenic is a highly toxic contaminant in drinking water and has long been a concern due to it's carcinogenic, mutagenic, and teratogenic effect on humans. Thus, the USEPA has set a new maximum contaminant level standard for arsenic in drinking water at 10 ppb, which will be effective in 2006. Polyelectrolyte-Enhanced Ultrafiltration, PEUF, has been used to remove low level arsenic contamination from drinking water, using a cationic polyelectrolyte poly(diallyldimethyl ammonium chloride), PDADMAC, to bind with the arsenate anion, allowing the solution to be treated using ultrafiltration. The economics of the process can be improved by reusing the PDADMAC. This work reports on the crystallization of low solubility calcium-arsenate compounds for the purpose of recovery of PDADMAC from the PEUF retentate stream. The crystallization experiments were conducted by adding calcium hydroxide to arsenate solutions both in the absence and presence of PDADMAC with varying Ca/As molar ratio, and pH. The products formed were characterized for phase identification, and crystal size and morphology using powder X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), thermal gravimetric analysis (TGA), and scanning electron microscopy coupled with energy dispersive X-ray fluorescence (SEM/EDX). The results from batch experiment as well as continuous experiment using a 500 mL MSMPR crystallizer will be discussed.