Downcycling of real electroplating sludge into nickel-rich solution for chemical nickel-plating

Abstract

The recovery of metals from electroplating sludge has gained significant attention due to the dual imperatives of resource valorization and environmental protection. To address these challenges, a simple, waste-liquid-free process was developed for efficiently recovering nickel from Ni-rich electroplating sludge, with subsequent in situ utilization for electroplating. The sludge consisted of 24.2 wt% Ni, 1.9 wt% Fe, 8.8 wt% Al, and 25.3 wt% moisture. After sulfuric acid leaching, a brief hydrothermal treatment was introduced to transform Fe and Al from the leachate into easily filterable natroalunite particles, yielding a purified Ni-rich solution with Fe and Al concentrations each below 0.1 g L⁻¹. Two main valorization routes for Ni were established. First, the purified solution serves directly as an electrolyte for nickel electrodeposition onto iron substrates, producing uniform, compact, and thermally stable coatings. This route achieves impressively high nickel recovery (nickel loss <2%) and avoids the need for organic additives or redox reagents, eliminating the generation of liquid waste. Second, downstream purification of the solution involves P204 extraction to further remove Fe and Al and extract Ni, followed by evaporation and crystallization to produce electroplating-grade NiSO₄ crystals (25.4 wt% Ni), compliant with industrial standards. Additionally, the natroalunite-rich by-products are readily filterable and hold promise as precursors for flocculant production. Overall, this process enables high-efficiency nickel recovery, minimizes secondary pollution, and provides versatile end-product options, highlighting its promise for sustainable resource utilization in the metal finishing sector.