A fresh sludge from a base metal operation failed on zinc and an aged sludge from a uranium mine failed on uranium. There are only three jurisdictions in Canada which have a regulated limit for zinc and this sludge would actually fail only in comparison to Qu bec's current regulation. It must be noted however, that Qu bec's proposed new regulated limits do not include zinc. The leachate concentrations from both tests were generally at least five times lower than the most stringent of the regulated limits. Therefore, fresh AMD treatment sludges would not generally be classified as hazardous wastes based on current leaching protocols and regulated contaminant limits.
Aged sludges are even less likely to be classified as hazardous wastes.
Based on the samples tested, this work has underlined that while sludge stability is an issue, greater emphasis should be placed on sludge disposal and volume reduction. Numerous leach protocols have been developed to test solid wastes. None of these leaching tests have been specifically designed for evaluating AMD treatment sludge leachability. A thorough review of regulatory and research leach protocols from Canada and the United States is provided. While regulatory leach tests for classification of hazardous wastes in Canada involve the use of acetic acid in the protocol, more appropriate tests, such as the Modified LEP, need to be considered for assessing the leachability of AMD treatment sludges for on-site disposal in a pond environment.