Leaching of Sm, Co, Fe, and Cu from Spent SmCo Magnets Using Organic Acid

Abstract

In this study, the Taguchi method was used to investigate the effect of citric acid and malic acid on the leaching of SmCo magnet waste. First, we used a L16(45) orthogonal table to conduct experiments. Second, we conducted a factor effect analysis on the experimental results of the orthogonal table to understand the influence of temperature, acid concentration, solid–to–liquid ratio, time, and hydrogen peroxide on the leaching efficiency and we obtained the priority order of the factors affecting the leaching efficiency. The priorities of citric acid and malic acid were H2O2 > temperature > S/L > time > acid and temperature > time > S/L > H2O2 > acid, respectively. Finally, the optimal leaching parameters were obtained through confirmation experiments. For optimal leaching rates with citric acid, the amount of hydrogen peroxide (H2O2) added was 2.0 vol.%, the temperature was 90 °C, the S/L ratio was 5 g L−1, the time was 135 min and the acid concentration was 1.0 mol L−1, resulting in leaching efficiencies of Sm, Co, Fe, and Cu of 87.62, 93.82, 97.10, and 92.84%, respectively. For optimal leaching rates with malic acid, the temperature was 80 °C, the time was 75 min, the S/L ratio was 7.5 g L−1, the amount of hydrogen peroxide added was 3.5 vol.%, and the acid concentration was 1.5 mol L−1, resulting in leaching efficiencies of Sm, Co, Fe, and Cu of 75.18, 74.58, 82.42, and 1.35%, respectively.