Characterization and Availability of Toxic Metals in Solid Mine Tailing: Ribeira Valley (Brazil)

Acid mine drainage formation and metal mobility is currently a great concern in abandoned mines. Ribeira Valley (Brazil) is an example of bad planning on closing inactive mines, where the waste was disposed directly on the soil near the river, without any protection and leaving the toxic metals capable of leaching. The aim of the present study was to evaluate the mobility and availability of toxic metals from a profile probing collected from a deposit of mining waste. To achieve this goal, simulations were carried out with different environmental conditions (pH very acid and natural). Geological and geotechnical characterization, leaching tests, solubilization and pH variation (3, 5 and 7) were performed. The results showed a predominance of sand fraction and high concentration of Zn and Pb in tailing. The mineralogy contains sulphite, carbonates and high concentration of barite and the pH of samples remained in neutral to alkaline, showing the impossibility of formation of acid drainage. The leaching and solubilization tests showed high concentration of extracted Pb, probably extracted from cerussite (carbonate), showing the mobility of this metal and classifying the waste as hazardous (according to Brazilian norm). Extraction with pH variation test exhibited significant metal release in all pH tested, including neutral one. In conclusion, waste does not generate acid drainage, even though in certain environmental conditions, such as acid or neutral pH, it may release toxic metal. The release of toxic metals can be toxic to biota. The tailing needs to be adequately covered to avoid any contact with animals or people who live near the river.