Trace element pollution of soils by abandoned gold mine tailings, near Potchefstroom, South Africa

摘要

Fine-grained material eroded by wind and water from tailings dams at the abandoned Machavie Gold Mine was deposited over an area of more than 1 km~2. The high acidity (average pH of 3.4) of the tailings caused sulphide minerals to decompose and form trace-element-rich leachate. Comparisons of the trace element content of the tailings and underlying soils with the Dutch-B soil standards indicated a potential contamination with As, Co, Cr, Cu and Ni. The degree of contamination and mobility of trace elements was determined by extraction with ammonium nitrate as the leaching agent. Mobilities were calculated by comparing total trace element concentration with extractable trace element concentration. Average trace element mobilities were generally higher in the tailings than in the underlying sandy colluvial and clayey alluvial soils and also showed an increase where the pH values of soils and tailings were lower than 5 and 3.5 respectively.