Effectiveness of Ion Exchange, Reverse Osmosis and Coagulation and filtration in the removal of Radioactivity from Acid Mine Drainage

Abstract

The aim of the study is to assess the effectiveness of ion exchange, reverse osmosis and coagulation filtration, three of the best available treatment methods, in the removal of radioactivity and heavy metals from Acid Mine Drainage (AMD) and make recommendations on the most appropriate method among the three that South Africa can employ in the treatment of AMD. Mine shaft AMD samples were collected from an AMD pumping station in the central basin of the Witwatersrand region. Another set of samples were collected from an AMD dam that has developed from abandoned gold mining operations. Temperature, pH, conductivity and Total Dissolved Solids were measured in the field during sampling. The samples were then analyzed for gross alpha and gross beta activity, metal concentration, anions and radionuclides. After analysis the samples were then treated using ion exchange, reverse osmosis and coagulation & filtration. Treated samples were then analyzed for gross alpha and gross beta activity and metal concentration. For treated mine shaft AMD the average gross alpha activity concentrations were 0.895±0.347 Bq/L, 0.045±0.035 Bq/L and 0.310±0.066 Bq/L for reverse osmosis, ion exchange and coagulation & filtration respectively. The gross beta activity concentrations were 0.083±0.004 Bq/L, 0.116±0.071 Bq/L and 0.696±0.105 Bq/L for reverse osmosis, ion exchange and coagulation & filtration respectively. The average gross alpha removal rates for reverse osmosis, ion exchange and coagulation & filtration were 77.87%, 98.03% and 87.80% respectively. The average gross beta removal rates for reverse osmosis, ion exchange and coagulation & filtration were 95.58%, 94.68% and 76.86% respectively. For treated surface AMD the average gross alpha activity concentrations were 2.346±0.347 Bq/L, 0.065±0.0375 Bq/L and 2.717±0.124 Bq/L for reverse osmosis, ion exchange and coagulation & filtration respectively. The gross beta activity concentrations were 0.186±0.014 Bq/L, 3.798±0.212 Bq/L and 5.847±0.267 Bq/L for reverse osmosis, ion exchange and coagulation & filtration respectively. The average gross alpha removal rates for reverse osmosis, ion exchange and coagulation & filtration were 96.24%, 99.90% and 95.63% respectively. The average gross beta removal rates for reverse osmosis, ion exchange and coagulation & filtration were 99.68%, 93.84% and 89.99% respectively. The World Health Organization guidance limits for gross alpha and gross beta activity in portable water are 0.5 Bq/L and 1 Bq/L respectively. According to the findings of this study ion exchange is the best method for the removal of both radioactivity and heavy metals from AMD, producing small amounts of solid waste and high radioactivity and metal removal rates.