Extraction of chloride from slag flush wastewater using solvent N235

Abstract

This work proposes a solvent extraction process for removal of chloride in slag flush wastewater using tri-n-octylamine (N235) as extractant. The single stage extraction and stripping efficiencies were 78.9% and 99.2% respectively under the optimal conditions. The McCabe-Thiele diagram and Kremser equation were utilized to predict the number of stages required to reduce the Cl− concentration to less than 350 mg/L. The results were authenticated utilizing a three-stage counter-current operation, that closely correspond the estimates of McCabe-Thiele diagram. The FT-IR spectra of organic phases indicate that the extractant N235 combines with H2SO4 first to form quaternary ammonium salt containing N-H+ after acidification by H2SO4, followed by an anionic exchange with Cl−. Further, the raffinate phase was stripped using a suitable stripping agent to increase the Cl− concentration up to 100,000 mg/L so as to facilitate precipitation of NaCl by addition of NaOH as salting-out agent. The XRD analysis was utilized to confirm the crystallinity and the purity of the precipitated NaCl.