The main goal of this study was to recover the cadmium and nickel content of waste zinc filter cake. In this regard, at first, the dissolution of these elements in sulfuric acid and optimization of the solution process were considered. Effects of various parameters such as dissolution reaction time (10–40 min), temperature (25–80°C), sulfuric acid concentration (2–11 vol.%), and particle size distribution (four size fractions) under liquid/solid ratio of 10 and stirring speed of 600 rpm on leaching of Cd dissolution from Cd–Ni filter cake were evaluated and optimized by Taguchi method. The experimental plan was designed using an orthogonal array, L16 (44), which denotes four parameters with four levels. The optimum dissolution conditions proposed by the Design Expert software were a reaction time of 40 min, temperature of 80 °C, sulfuric acid concentration of 8 vol.%, and particle size distribution of −75 + 53 μm with predicted dissolution content of Cd equals to 93.15% by the software. In the optimum condition, 95.2% of the Cd content was leached during the verifying test. According to the results, reaction time, particle size distribution, acid concentration, and temperature are the most affecting parameters on Cd dissolution, respectively. Separation of Ni and Cd present in the solution after dissolution using sodium sulfate precipitation in the pH range of 1–5 was studied at the second stage, and the results show that at pH = 3, maximum separation of Ni and Cd (with weight ratio of Cd to Ni in the precipitates equals to 46.2) was achieved.
