Lead extraction as metallic phase from waste lead oxide-containing glass by redox reaction in hydrothermal treatment

Abstract

A new low-energy and eco-friendly method for extracting lead from waste PbO-containing funnel glass is required. Conventional methods use either energy intensive smelting reduction at temperatures higher than 1273 K or involve phase separation of the glass, requiring an acid treatment to extract elemental Pb partitioned in one of the decomposed phases as Pb2+ ion. In this study, the mechanism of a unique phenomenon is investigated, involving spontaneous precipitation of metallic lead when PbO-containing glass is subjected to a hydrothermal water environment in a stainless-steel container. The roles of the hydrothermal environment and container materials on the metallic lead precipitation were investigated. The synthesized PbO-containing glass was placed in a container made of stainless steel or pure iron and set in a sealed autoclave with water, which was held at 613 K to provide the hydrothermal conditions. As a result, metallic lead droplets precipitated either on the surface of the glass or the container, whereas an iron oxide (Fe3O4) phase was detected on the surface of the container. Conversely, no metallic lead was observed when the glass and stainless-steel container were heated in dry air. The above results indicate that a hydrothermal environment is necessary for metallic lead precipitation because subcritical water or steam leaches Pb2+ from the glass. In addition, a redox reaction was suggested between the Pb2+ ions transported to the surface of the container and metallic iron in the container to explain metallic lead droplets precipitation.