LEACHING CHARACTERISTICS OF HEAVY-METALS FROM 3 HISTORICAL PB-ZN MINE TAILINGS 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 programme that was chosen to represent periods of one and two years at three 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 temperature 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 leachates 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-degrees-C (+/-3-degrees-C). The concentrations of Cd and Zn in the tailings leachates showed no marked difference at the different temperatures. The composition of the leachate was found to be dependent on the type of gangue mineral, the presence of other sulphide minerals and the formation of secondary iron minerals. A comparison of the concentrations of 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.