A resins-neutralization coupled route for the treatment of stainless-steel pickling effluent: A research study

Abstract

One of the major environmental problems caused by stainless-steel industries is the liquid effluents generated during the production processes. It contains a high concentration of metal ions such as Fe (III), Cr (III), Cr (VI), and Ni (II) in HF and HNO3 mixture, oil, and rinse wastewater. The used pickling waste stream has a pH of 0.5 and Total Dissolved Salts (TDS) of 520g/L with a density of 1.20g/CC. The present work focused on recycling pickling effluent by combining filtration, resins, and neutralization to remove metal ions efficiently and F- greater than 99.5%. To remove TDS, laboratory experiments were performed using micro and ultra-filters with a membrane area 0.2m2. Cr (VI) was removed using TulsionFSMP 6301 resin and desorption using NaNO3 and subsequent conversion into Na2Cr2O7 as a by-product. For neutralization, Ca(OH)2 and NaOH were used to precipitate metal ions, and the resulting filtrate was polished using ZrOCl2 to remove F- to 0.12 mg/L effectively. The nitrate was recovered as NaNO3. Adsorption isotherm and kinetic studies were utilized for Cr (VI) from experimental data, and a process flow diagram was developed, which can eventually be tested on a larger scale.