The basin acidification affected by AMD: A case study in Xingren county, Guizhou, China

Pyrite oxidation at mine sites has been blamed for the acid mine drainage (AMD), which becomes a long term environmental problem in the basin scale. A typical closed mine site in Xingren, Guizhou was chosen to investigate the variation of pH in the AMD and surface water and its effects on the basin acidification. The pH value was found to be around 3.0 in the AMD and acidic water reservoir. When the acidic water flows, it reacted with the rock blocks of limestone in the river. At the same time, AMD has a typical orange or ocherous appearance which is due to the iron hydroxide that is formed during the oxidation. The iron hydroxide precipitates as sludge, forming a coat on river bottom and bank that prevents further reaction of acidic water with the river bed. It was found that the pH value in surface water was kept low even 5km downstream of the sources AMD. The most frequent pH values in soil samples with and without acidic water irrigation were 5.0 and 6.5, respectively, indicating soil acidification within the basin.