Gold, Silver and Iron in Iron Oxy-hydroxide Precipitate Formed in Process of Acid Mine Drainage

Oxidation of sulfide containing ores is main cause of Acid mine drainage (AMD), which is environmental problem associated with both abandoned and active mines. Iron-bearing sulfide minerals can be oxidized and form mine waters with high sulfate content, low pH, high electrical conductivity, high redox potential and high concentrations of iron, aluminum and other heavy metals. In the process of acid mine drainage precipitation of poorly crystalized oxy-hydroxides of iron with large active surface can occur. On the surface of iron oxy-hydroxide precipitated particulate matter, anions and cations (metals) could be adsorbed. Mine waters can contain a certain amount of precious metals, which could also be adsorbed onto iron particulate matter surface, which was investigated in this research. In this study, samples of iron oxy-hydroxide particulate matter at abandoned gold mine waste in Bakovici (Central Bosnia and Herzegovina) were used. Several parameters were measured on the selected mine waste samples: pH, water content, particle size distribution, sulfate content, electrical conductivity, redox potential, and amounts of gold, silver and iron. The results indicate that significant amount of gold (average: 6.8 mg/kg), and silver (average: 7.13 mg/kg) are present in iron precipitate. Adsorption of precious metals onto iron oxy-hydroxide surface is strongly pH dependent. At very low pH which was found in investigated samples, desorption of precious metals is favorited. Thus, precious metals are only partially adsorbed onto iron oxy-hydroxide surface.