Recovery of Metals from Sludges and Wastewaters

This report presents information on the state-of-the-art of metals recovery technologies to assist in identifying waste-management options for metalbearing sludges and wastewaters that may be regulated under the Resource Conservation and Recovery Act (RCRA). Only a few of the technologies addressed In this report (e.g., electrowinnlng, high-temperature metals recovery (HTMR]) are directly applicable to the recovery of metals from wastes; other technologies treat the wastes to a physical form that may be amenable to eventual metals recovery. Wastewaters can be treated effectively by several methods. Precipitation processes have been widely used to remove arsenic, cadmium, chromium (+3), copper, Iron, manganese, nickel, lead, and zinc from metal-bearing wastewaters. For economic reasons, electrowinning is a commercial technology that has normally been restricted to the treatment of wastewaters contalnlng noble metals such as gold and silver. After appropriate pretreatment, sludges can be effectively treated by HTMR processes. These processes allow for the direct recovery of metals from sludges. The economic feasibility depends on the amount of sludges treated and the amount of metals contained In the sludges. Membrane separation processes such as mlcrofiltration (MF) and ultrafiltration (UF) can be used In combination wlth chemical treatment for the physical separation of metal sludges. Leaching may be used to extract cadmium, chromium, copper, lead, nickel, and zinc directly from sludges by using various process trains. This Project Summary was developed by EPA’s Risk Reduction Engineering Laboratory, Cincinnati OH, to announce key findings of the research project that is fully documented in a separate report of the same title (see Project Report ordering information at back).