Application of ion exchange and chemical precipitation process for the treatment of acid-dissolution water of chromium sludge

The purpose of this study was to selectively remove chromium from acid-dissolution water of chromium sludge using the continuous column and precipitation techniques. Column experimental results indicated that the Thomas model was found to predict reasonably well the ion exchange breakthrough performance. The best adsorption and desorption capacities occurred at 7.5 mL/min flow rate and low 150 mg/L Cr (III) solutions for all adsorbents. The cyclic experiments' results showed that chromium had the same sorption and elution pattern in the four sequences in synthetic solutions, while removal and elution efficiencies were decreased over the four cycles in acid-dissolution water. After passing 2.5% NaCLO-treated acid-dissolution water through IRN77 columns, IRN77 resin did not show any signs of performances diminution over the four consecutive sorption and elution cycles. The adsorption efficiency could reach 37% which was 62% of that in synthetic solution, and the elution efficiency remained above 95%. Residual chromium after successive treatments of acid-dissolution water with IRN77 could be extracted by coagulation-precipitation treatment with NaOH/MgO mixtures. This process led to the final effluent which contained less than 0.5 mg/L of chromium. The results suggested that the combination of oxidation/resin and coagulation-precipitation could make the advanced reuse of acid-dissolution water become a reality.