ACID-FORMING CAPACITY OF LEAD-ZINC MINE TAILINGS AND ITS IMPLICATIONSFOR MINE REHABILITATION

Acid mine drainage problems were experienced in a Pb-Zn mine operation at Lechang, in the northern part of Guangdong Province, People's Repu blic of China. Geochemical and acid generation evaluations were made o n fresh tailings including tailings fine, tailings sand and high sulph ide tailings, and oxidised tailings with the aim of providing informat ion on mine rehabilitation. All fresh tailings had a pH higher than 7 while the oxidised tailings had a pH of 4.9 (range 1.6 to 7.4). Only s amples with pH < 3 had an electrical conductivity (EC) > 4 dS m(-1). T otal S contents of all tailings samples were very high with the high s ulphide fraction having a mean S content of 38%. All fresh tailings ha d a high acid neutralisation capacity (ANC) while half of the oxidised tailings had an ANC less than zero. The results from the acid-base ac count and the net acid generation test indicated that all fresh and ox idised tailings samples were acid-forming except for the sand fraction samples. AII tailings samples contained high total concentrations of Cd, Cu, Fe, Pb and Zn but low concentrations of total nitrogen and pho sphorus. The preliminary results demonstrated that the tailings were a ll acid-forming especially the high sulphide fraction which should be kept permanently unexposed under impermeable cap or water.