Treatment of Berkeley Pitlake Water Using the Green Precipitate Process

Acid mine drainage (AMD) is usually treated by air oxidation followed by addition of lime to precipitate metal hydroxides and calcium sulfate. Geo2 Limited of Melbourne, Australia, has developed and patented a novel alternative precipitation scheme based on the formation of mixed valency, M(II)-M(III), hydroxide sulfate salts. When the composition of AMD has an appropriate ratio of Fe(II):Fe(III), the green precipitate process provides a useful and more effective alternative to conventional liming. Many acidic mine drainage waters consist predominantly of Fe(II), particularly near their source, and it is these where the green precipitate (GP) process can be used with most positive effect. The GP process incorporates a pipe reactor to prevent or control oxidation. The characteristics of the precipitate and utility of the green precipitate process are described here in terms of underlying chemistry and innovative process equipment. Demonstrations in the United States where Berkeley Pitlake water was treated are described. A mobile, pilot pipe reactor rig was built to demonstrate the process and was used successfully in these trials in Butte, Montana.