Recovery of nickel from spent multilayer ceramic capacitors: A novel and sustainable route based on sequential hydrometallurgical and photocatalytic stages

The depletion of primary metal sources and the extensive use of nickel necessitate its extraction from secondary resources. In this study, we employed a chloride-based solution containing cupric ions (NaCl/CuCl2) to enable a straightforward recovery process for nickel from Ni-containing waste materials. Prior to application in real systems, we evaluated different operating conditions using metallic nickel particles, including chloride and cupric ion concentrations, system temperature, and pH. Optimal efficiency was achieved at T = 60 °C, pH = 5.0, [Cu(II)]0 = 5.0 × 10-3 M, and [Cl]0 = 6.0 M, resulting in complete dissolution of metallic Ni (58 ppm) within 180 min. This optimized leaching system was then applied to exhausted nickel-containing multilayer ceramic capacitors (MLCCs) matrixes, leading to 80% Ni recovery. FESEM-EDX and XRD analysis characterized both synthetic and real matrixes. Additionally, we proposed a viable route for selective metal recovery through precipitation and photodeposition on titanium dioxide. Complete copper photodeposition occurred after 150 min, while Ni precipitation as Ni(OH)2 was achieved by adjusting the solution pH to 10. Experimental data from runs with the synthetic matrix were analyzed using a shrinking spherical particle model.