Nickel recovery from Raney nickel by leaching and precipitation: towards resource valorisation

Spent catalysts are often rich in valuable metals and are typically discarded, leading to both resource loss and environmental issues. Recovering nickel from spent catalysts is thus crucial for improving resource efficiency and sustainable resource use. In the present study, nickel was recovered from a Raney Nickel catalyst via acid leaching with sulphuric acid and precipitation with sodium hydroxide. The effects of acid concentration on leaching process and the effect of pH on precipitation process were investigated. The leaching process was carried out using sulphuric acid at concentrations of 3, 4, 4.5 and 5.5 M, and the solid residue from the leachate solution was separated by filtration. Later, the pH of the leach solution was adjusted to 5 M NaOH to precipitate nickel. Nickel recovery was investigated as a function of sulphuric acid concentrations in the leaching process and the solution pH in the precipitation process. It was found that 4.5 M H₂SO₄ yielded the highest nickel recovery of 68.13%. Using 4.5 M H₂SO₄ for leaching and pH 14 of NaOH precipitation, the presence of nickel and nickel oxide was confirmed using XRD in the precipitate. The leaching rate was further increased by using 4.5 M H₂SO₄ (k = 0.1805 h⁻¹), with greater acid strength and pH control than 3 M (k = 0.0466 h⁻¹), confirming the strong relationship between these key parameters to optimise nickel recovery. Overall, these findings indicate that acid leaching–alkali precipitation will be an efficient and scalable technique for nickel recovery from spent catalysts, facilitating resource recycling and waste reduction.