Separation and extraction of amphoteric metals from waste printed circuit board powders by low-temperature alkaline smelting

Multi-component metal powders were prepared by imitating the crushed metal enrichment originated from waste printed circuit boards. The effects of smelting temperature, smelting time and NaNO₃-NaOH/powder mass ratio on the extracting ratios of amphoteric metals during low-temperature alkaline smelting were investigated through single-factor experiments and orthogonal tests. It is found that the mass ratio of NaNO₃-NaOH to crushed metal enrichment has the most significant effect on the extracting ratios of amphoteric metals. The optimum conditions were obtained as the smelting temperature of 400℃, the smelting time of 1.5 h and the mass ratio of NaNO₃-NaOH to crushed metal enrichment of 3.5. Under the optimum conditions, the extracting ratios of amphoteric metals are as the following:Sn 83.6%, Al 92.7%, Zn 80.9%, and Sb 34.5%. Amphoteric metals are converted to sodium salts, dissolving in the leaching process, while other components, such as copper and precious metals, are enriched in the residue. In this novel process, amphoteric metals are separated with other metals efficiently.