14:15 〜 14:30
[HRE12-03] Geochemical Characterization of Rivers Contaminated by Acid Mine Drainage from an Abandoned Mine in Northern Japan
キーワード：Natural attenuation, Schwertmannite , Adsorption
Acid mine drainage (AMD) of an abandoned mine in northern Japan riches of Fe, As, Pb, and Cd, has been flowing into river A and B. At the monitoring point, the contaminants of river A decreased to below the environmental standard level. In contrast, river B's contaminants remain slightly higher than the environmental standard level, even though the two rivers have the same contamination source. The natural process in river A makes the contaminants attenuated, but not in the river B. If the geochemical differences between A and B are well understood, information from the two rivers is ambiguously valuable for the geochemical passive treatment in river B. Therefore, river A and river B detail studies were investigated to determine the geochemical differences in both rivers, and define the natural attenuation mechanisms in river A.
AMD from both rivers contains a high ferric iron concentration with an average pH of 2.8. After AMD having mixed with the natural river water, river A's pH is 3.1. The formation of schwertmannite (ferric hydroxide sulfate mineral) appears on the riverbed. At the mixing point, As concentration decrease due to its adsorption on to schwertmannite surface. Yet, the concentrations of Pb and Cd were decreased by dilution of the natural water in river A. Oppositely, the pH of AMD in river B pH is 2.9 after mixing with the natural river water. No reduction of dissolved ferric, As, Pb, and Cd concentrations, neither precipitation of ferric minerals such as schwertmannite, were significantly found after the mixing in river B. Dilution of the natural river water plays an important role to make the geochemical differences in the study area. The mixing ratios of both rivers to the natural water do not only control the pH changes, but it is also responsible for the decreasing of the contaminants’ concentration in the rivers. The dilution ratio of river A to the natural water is comparatively more than it is in river B. Learning from the natural attenuation process in river A, the geochemical passive treatment of river B is applicable by increasing pH to 3.2 by using a dilution method and an open limestone channel.
AMD from both rivers contains a high ferric iron concentration with an average pH of 2.8. After AMD having mixed with the natural river water, river A's pH is 3.1. The formation of schwertmannite (ferric hydroxide sulfate mineral) appears on the riverbed. At the mixing point, As concentration decrease due to its adsorption on to schwertmannite surface. Yet, the concentrations of Pb and Cd were decreased by dilution of the natural water in river A. Oppositely, the pH of AMD in river B pH is 2.9 after mixing with the natural river water. No reduction of dissolved ferric, As, Pb, and Cd concentrations, neither precipitation of ferric minerals such as schwertmannite, were significantly found after the mixing in river B. Dilution of the natural river water plays an important role to make the geochemical differences in the study area. The mixing ratios of both rivers to the natural water do not only control the pH changes, but it is also responsible for the decreasing of the contaminants’ concentration in the rivers. The dilution ratio of river A to the natural water is comparatively more than it is in river B. Learning from the natural attenuation process in river A, the geochemical passive treatment of river B is applicable by increasing pH to 3.2 by using a dilution method and an open limestone channel.