Leaching of metastannic acid from e-waste by-products

Abstract

Anode slime and tin precipitate as by-products of the electrorefining (ER) of non-standard anodes obtained after experimental smelting of waste electric and electronic equipment (e-waste), in addition to the base and precious metals, contains a significant amount of tin. Due to its presence as inert SnO2 hydrate (β metastannic acid) and its dissipation between slime and electrolyte, anode slime processing and metals valorization are difficult. This study aimed to investigate conditions under which efficient leaching of metastannic acid could be achieved to facilitate further metals valorization, especially precious metals. The investigation was performed using the by-products obtained from the ER of the non-standard Cu anodes produced by pyrometallurgical processing of e-waste. After detailed characterization of obtained products, the influence of various process parameters like temperature, acid concentration, leaching time, as well as the influence of reducing agent, sulfur compounds, and SnO2 hydration rate on leaching efficiency was investigated. It was found that efficiency of 99% can be achieved by leaching the desulfurized tin precipitate sample in 6 M HCl at 90 °C for 90 min with the addition of Mg powder. The application of the tin removal process, described in this paper, contributes to efficient material flow management.