TRANSPORT AND FATE OF SELECTED HEAVY METALS IN CIRCUMNEUTRAL RIVER ENVIRONMENT: A CASE STUDY OF THE RIVER NENT CUMBRIA, ENGLAND

The research investigates the transport and fate of heavy metal entrenchment into the River Nent from abandoned spoil waste at the former mine site. The River Nent is found to maintain a circum-neutral pH and contains high concentrations of dissolved zinc (Zn) and lead (Pb) of 0.70mg/l and 0.08mg/l respectively at flow rate of 34.5l/s. Relative concentration of sulphate and carbonate ions is observed to influence the river pH. This condition has a marked effect on the concentrations of Zn and an insignificant effect on Pb, copper (Cu), cadmium (Cd) and nickel (Ni). A leaching experiment shows that loosely-bound Zn minerals in spoil waste, when entrained into the river, quickly go into solution causing a sudden rise in dissolved Zn concentration. However, some of the dissolved Zn will precipitate further downstream as carbonate, thereby lowering the amount of dissolved zinc in the water column. A similar leaching test also indicates that under acidic condition of ~ pH 5, concentrations of dissolved SZn and Pb in solution will continue to increase with zinc being about 3 times higher than Pb. If pH is maintained for a long time, the concentrations of both metals continue to rise, except enough carbonate is dissolved. This condition was observed not to affect the dissolution of Pb minerals.