Efficient recovery of Fe (III) from dechroming sludge with a novel combined process of acidic leaching and on-line adsorption

Iron, a prevalent impurity in dechroming sludge (DCS), poses a major challenge to the recovery and purification of valuable metals such as Cu, Ni, and Zn in wet processing. There is an urgent need for an efficient and selective iron separation technique that minimizes the loss of Cu, Ni, and Zn. In this study, an innovative combined approach of acid leaching and on-line adsorption was developed to selectively recover Fe 3 + from DCS. Results indicated that acid leaching with 0.05 mol/L H 2 SO 4 achieved extraction efficiencies of 98.2% for Fe 3+ , 99.0% for Cu 2+ , 94.6% for Ni 2+ , and 96.5% for Zn 2+ , yielding a leachate containing approximately 93.5 mg/L Fe 3+ . A phosphonic acid-functionalized resin (X-Fe resin) was then used to selectively remove Fe 3+ from the leachate. Batch adsorption experiments demonstrated higher adsorption capacity, rapid kinetics, and good reusability of the resin. Dynamic adsorption tests in the unitary, binary, and ternary systems revealed an affinity order of Fe 3+ >Cu 2+ >Zn 2+ >Ni 2+ , with competitive substitution favoring selective Fe 3+ uptake. EDS-mapping (Energy-Dispersive X-ray Spectroscopy mapping), XPS (X-ray Photoelectron Spectroscopy), and DFT (Density Functional Theory) analysis demonstrated that the high adsorption affinity was due to the more negative binding energy between Fe 3+ and the resin. When treating the DCS, the dynamic on-line adsorption process efficiently recovered of 95.3% of Fe 3 ⁺, and the final effluent had less than 5.0 mg/L Fe, meeting the requirements for industrial production standards. This work focuses on an innovative combination process of acid leaching and selective adsorption for iron removal, which offers a sustainable route for purification and resource recovery in a hydrometallurgical process.