Separation of chloride and sulphate ions from nanofiltration rejected wastewater of steel industry

Scheme for precipitation of salts from NF rejected steel industry wastewater [Display omitted] •Separation of Cl− and SO4-2 ions from nanofiltration reject of steel industry was studied.•Ions are removed by solventing out effect using diisopropylamine, isopropylamine and ethylamine.•Effects of volume ratio (VR), pH, temperature and contact time was investigated.•Cl− and SO4-2 removal was found 77.50 % and 99.82 %, respectively at VR = 1.02, pH = 8, at 23 °C. This work focused on the removal of chlorides and sulphates from nanofiltration rejected water of steel industry by the method of precipitation using miscible organic solvents such as diisopropylamine (DIIPA), isopropylamine (IPA), and ethylamine (EA) in different proportions. Solvent based precipitation showed that miscible organic solvents such as DIPA/IPA/EA is effective in precipitating salts from NF rejected water and thereby reducing the concentrations of chlorides and sulphates. Effects of solvent to water ratio, pH, temperature and mixing time was thoroughly investigated. Sulphate and chloride removal efficiency of 99.82 % and 77.50 % respectively, was observed. The treated water can be reused to the system or discharged safely to the environment. Response surface methodology (RSM) was applied to optimize the parameters for the removal of chloride and sulphate ions. Analysis of variance was used to study the incurred data, which then fitted to the second-order quadratic equation, by regression. Four important parameters namely volume of the solvent, pH, temperature and contact time were optimized using central composite design (CCD). Up to 98 % of solvent was recovered by simple distillation for further use. The precipitated salts were characterized by FESEM, XRD and FTIR analysis.