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

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 the recycling of pickling effluent by applying a combination of filtration, resins, and neutralization for the efficient removal of metal ions and F- greater than 99.5%. Laboratory experiments were performed using micro and ultra-filters with a membrane area of 0.2m2 for the removal of TDS. 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, NaOH were used to precipitate metal ions and the resulting filtrate was polished using ZrOCl2 for effective removal of F- to 0.12 mg/L. The nitrate was recovered as NaNO3. Adsorption isotherm and kinetic studies were utilised for Cr (VI) from experimental data and a process flow diagram is developed, which can eventually be tested on a larger scale.