LEACHING CHARACTERISTICS OF HEAVY-METALS FROM 3 HISTORICAL PB-ZN MINETAILINGS HEAPS IN THE UNITED-KINGDOM

Tailings from three historical mining areas in the United Kingdom were leached in columns in the laboratory under a simulated weathering pro gramme that was chosen to represent periods of one and two years at th ree different ambient temperatures. The total concentrations of Cd, Cu , Pb and Zn in the primary ore minerals present in the tailings showed only a limited correlation with metal concentrations in the leachate. The leachate from columns of tailings that were maintained at a tempe rature of 25-degrees-C (+/-3-degrees-C) contained on average 50% more Pb and 75% more Cu than leachate from tailings that were maintained at a temperature of 10-degrees-C (+/-3-degrees-C). The pH values of leac hates from all three types of tailings at 25-degrees-C (+/-3-degrees-C ) were 0.2 units lower than those from columns maintained at 10-degree s-C (+/-3-degrees-C). The concentrations of Cd and Zn in the tailings leachates showed no marked difference at the different temperatures. T he composition of the leachate was found to be dependent on the type o f gangue mineral, the presence of other sulphide minerals and the form ation of secondary iron minerals. A comparison of the concentrations o f heavy metals in the leachates produced in the laboratory with those in leachates that were collected in the field over a similar period of time from two of the mine sites showed that concentrations were of a similar order.