Ion-exchange (IX): arsenic and chromium removal from brines and removal of inorganic contaminants by specialty resins

Although ion exchange is highly efficient in removing inorganic contaminants, similar to other water treatment technologies, ion exchange has some drawbacks that need to be studied further. Three issues related to drawbacks of ion-exchange resins in water treatment were addressed in this research. The first issue was the influence of anionic inorganic co-contaminants including nitrate, Cr(VI), Se(VI), and As(V) on the performances of nitrate and perchlorate specialty (selective) resins in water treatment. It was found that nitrate can be removed from waters using perchlorate specialty resins, but the resin is poorly regenerated. Perchlorate was not easily removed from either nitrate or perchlorate specialty resins. The results showed that simultaneous removal of nitrate and Cr(VI) is optimal when using nitrate specialty resin. Perchlorate/nitrate specialty resins were inefficient in removing As(V), but could exchange Cr(VI) or Se(VI). A major issue realized from this research is the accumulation of co-contaminants in specialty resins and their release during resin regeneration. Such a release may deem waste regenerant brines hazardous, significantly affecting disposal costs. The presence of the co-contaminant ions affected the run length and the brine composition when perchlorate or nitrate specialty resins were used. Brine treatment is a serious challenge for IX water industry when removing arsenic (V) or chromium (VI) from drinking water. Arsenic (V) removal from brines using ferric chloride was the second issue of this research. The optimum pH range for the process was found to be 4.5-6.5. Higher brine alkalinity affected coagulation because it commands larger amounts of acid to lower the pH to the desired level. Increasing ionic strength slightly enhanced the arsenic (V) removal efficiency. For arsenic (V) concentrations typical in ion exchange brines and to achieve a remaining As (V) concentration of 5 mg/L, Fe/As molar ratios varying from 1.3 to 1.7 are needed at operating pH values of 5.5 to 6.5. The Fe/As ratios needed to treat brines are significantly lower than those used to treat drinking waters. Solids concentration varying from 2 to 18 mg/L were found. The third issue of this research was chromium removal from IX brines. Optimum pH range for the process was found to be 8-10.3. The chromium removal efficiency improved only slightly when the ionic strength increased from 0.1 M to 1.5 M. For chromium (VI) concentrations typically found in IX brines, a CaS5/Cr(VI) molar ratio varying from 0.6 to 1.4 was needed to obtain a final chromium concentration below 5 mg/L. The maximum total chromium removal efficiencies were obtained at reducing conditions when oxidation reduction potentials of the brines were between -0.1 to 0 V. Solids concentrations varying from 0.2 to 1.5 g/L were found. The results of this research have direct application to the treatment of residual wastes brines containing chromium

Surface Complexation Modeling of the Removal of Arsenic from Ion-Exchange Waste Brines with Ferric Chloride

Brine disposal is a serious challenge of arsenic (V) removal from drinking water using ion-exchange (IX). Although arsenic removal with ferric chloride (FeCl3) from drinking waters is well documented, the application of FeCl3 to remove arsenic (V) from brines has not been thoroughly investigated. In contrast to drinking water, IX brines contain high ionic strength, high alkalinity, and high arsenic concentrations; these factors are known to influence arsenic removal by FeCl3. Surface complexation modeling and experimental coagulation tests were performed to investigate the influence of ionic strength, pH, Fe/As molar ratios, and alkalinity on the removal of arsenic from IX brines. The model prediction was in good agreement with the experimental data. Optimum pH range was found to be between 4.5 and 6.5. The arsenic removal efficiency slightly improved with higher ionic strength. The Fe/As ratios needed to treat brines were significantly lower than those used to treat drinking waters. For arsenic (V) concentrations typical in IX brines, Fe/As molar ratios varying from 1.3 to 1.7 were needed. Sludge solid concentrations varying from 2 to 18 mg L−1 were found. The results of this research have direct application to the treatment of residual wastes brines containing arsenic

Chromium Removal from Ion-Exchange Waste Brines with Calcium Polysulfide

Chromium removal from ion-exchange (IX) brines presents a serious challenge to the water industry. Although chromium removal with calcium polysulfide (CaS5) 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, CaS5/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 CaS5/Cr(VI) molar ratio varying from 0.6 to 1.4 was needed to obtain a final chromium concentration /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 CaS5 dosage. The results of this research are directly applicable to the treatment of residual waste brines containing chromium

Impacts of Cocontaminants on the Performances of Perchlorate and Nitrate Specialty Ion-Exchange Resins

The influence of anionic inorganic cocontaminants including nitrate, Cr(VI), Se(VI), and As(V) on the application of nitrate and perchlorate specialty resins in water treatment was investigated. It was found that nitrate can be removed from waters using perchlorate specialty resins, but the resin is poorly regenerated. Perchlorate was not easily removed from either nitrate or perchlorate specialty resins. Simultaneous removal of nitrate and Cr(VI) was optimal when using nitrate specialty resin. Perchlorate/nitrate specialty resins were inefficient in removing As(V), but can exchange Cr(VI) or Se(VI). A major concern is the presence of high levels of Cr(VI), As(V), or Se(VI) in the waste brine, which affects waste brine disposal and cost. Perchlorate specialty resins showed very low run length for Cr(VI), As(V), or Se(VI). Nitrate specialty resins were very efficient in removing Cr(VI), and they can be easily regenerated