title: Chromium removal from ion-exchange waste brines with calcium polysulfide.
abstract: Chromium removal from ion-exchange (IX) brines presents a serious challenge to the water industry. Although chromium removal with calcium polysulfide (CaS(5)) from drinking waters has been investigated somewhat, its removal from ion-exchange brines has not been evaluated to date. In this study, a Central Composite Design as well as experimental coagulation tests were performed to investigate the influence of pH, CaS(5)/Cr(VI) molar ratio, alkalinity, and ionic strength in the removal of chromium from IX brines. The optimal pH range for the process was found to be pH 8-10.3 and brine alkalinity did not affect coagulation. The efficiency of chromium removal improved only slightly when the ionic strength increased from 0.1 M to 1.5 M; no significant difference was observed for an ionic strength change from 1.5 to 2.1 M. For chromium (VI) concentrations typically found in ion-exchange brines, a CaS(5)/Cr(VI) molar ratio varying from 0.6 to 1.4 was needed to obtain a final chromium concentration <5 mg/L. Maximum efficiency for total chromium removal was obtained when oxidation reduction potentials were between -0.1 and 0 (V). Solids concentrations (0.2-1.5 g/L) were found to increase proportionally with CaS(5) dosage. The results of this research are directly applicable to the treatment of residual waste brines containing chromium.
authors.affiliation: Department of Civil and Environmental Engineering, University of Nevada, 4505 S. Maryland Parkway, Las Vegas, NV 890154-4015, USA.
authors.forename: Behrang
authors.initials: B
authors.lastname: Pakzadeh
authors.forename: Jacimaria R
authors.initials: JR
authors.lastname: Batista
mesh_terms: D000468:Alkalies / Q000737:chemistry; D000704:Analysis of Variance; D017610:Calcium Compounds / Q000737:chemistry*; D002857:Chromium / Q000302:isolation & purification*; D006863:Hydrogen-Ion Concentration; D007474:Ion Exchange; D008956:Models, Chemical; D009994:Osmolar Concentration; D010084:Oxidation-Reduction; D012044:Regression Analysis; D012492:Salts / Q000737:chemistry*; D013440:Sulfides / Q000737:chemistry*; D013885:Thiosulfates / Q000737:chemistry*; D014865:Waste Disposal, Fluid
chemical_list: D000468:Alkalies; D017610:Calcium Compounds; D012492:Salts; D013440:Sulfides; D013885:Thiosulfates; C017082:brine; D002857:Chromium; C033907:calcium sulfide