Three strategies to treat reverse osmosis brine and cation exchange spent regenerant to increase system recovery

Concentrate streams from industrial processes entail an important risk for the environment, as they are often discharged into it. Therefore, efforts must be made to reduce the load of contaminants discharged to the environment. Eutectic freeze crystallization (EFC) is a novel technique which allows separation of salts and water from aqueous streams. In this research, three treatment options for reverse osmosis (RO) concentrate and cation exchange (CIEX) spent regenerant are investigated.First, application of EFC to RO concentrate was investigated. The stream was rich in HCO₃^- and Na⁺. Application of EFC to this solution, led to the formation of ice and NaHCO₃ at -3.9°C with 5.8wt.% NaHCO₃.Second, precipitation of CaCO₃ by mixing the RO concentrate with the CIEX regenerant in a ratio of 2.8:1 and adjusting the pH to 11 was investigated. A 0.25M NaCl solution remained after the treatment, which upon concentration could be used to regenerate the resin.Third, application of EFC to a synthetic CIEX regenerant was also investigated. The multicomponent solution contained NaCl, MgCl₂ and CaCl₂. Upon EFC treatment, ice formed first and then NaCl·2H₂O at -29°C. The composition of eutectic point at -29.4°C was 2.48wt.% Na and 15.85wt.% Cl.