Novel extraction process for the recovery of copper from wastewater treatment sludges

A hydro-pyrometallurgical process has been developed to recycle metals such as copper and lead from EPA designated F006 wastewater treatment sludges leaving a delisted residue suitable for Subtitle D disposal. Currently, thousands of tons of EPA F006 sludge are being landfilled as Subtitle C (hazardous) waste each year which is an undesirable alternative for these waste products because of the toxic metal content, such as cadmium and lead, that may be potentially leachable if the landfill fails. Conventional treatment consists of smelting (if the copper content is above 15%) or using acids or bases to solubilize the metals for subsequent separation and recovery. Unfortunately, waste products are still produced (for example, slag or leach residues) that must be disposed as hazardous waste. A process has been developed using a polyamine to extract copper for subsequent recovery using solvent extraction. Sulfuric acid is used to strip the copper from the solvent extractants and electrowon to produce cathode metal. Removal of the residual amounts of lead, zinc and cadmium from the leach residue is achieved by roasting at 1000°C. The volatilized metals are recovered in a baghouse for further treatment. The roaster residue can then be disposed in Subtitle D landfill facilities as it passes the Toxicity Characteristic Leaching Procedure for F006 wastes generically delisted under EPA Finalized Rules (Federal Register, Vol. 57, No. 160, Tuesday, August 18, 1992/Rules and Regulations.) --Abstract, page iii