This study was conducted to investigate the selective precipitation and recovery of high purity precipitate which can be recycled at the dissolved heavy metals contained in acidic mine drainage (AMD) through pH control.
First, experiments were carried out on the precipitation characteristics according to pH changes in each single solution and mixed solution of Five heavy metals such as Fe, Al, Cu, Zn and Mn in order to selectively separate the heavy metals contained in the acid mine drainage. Experimental results in mixed solution, which is similar to actual mine drainage, Fe was started to precipitate at pH 4.0 and was completed at pH 6.0, Al precipitates at pH 5.0 and was completed at pH 6.0, but characteristically has the property that the Al precipitate is re-dissolved from pH 8.0 or higher. It was confirmed that precipitation occurred at pH 6.0-pH 8.0 for Cu, pH 8.0-10.0 for Zn and 9.0-10.0 for Mn.
Secondly, the selective precipitation and recovery of high-purity precipitates of each precipitates from mixure solution of Fe and Al were carried out using the characteristics of the above-mentioned Al precipitates being re-dissolved at a pH of 8.0 or higher. In the mixed solution of Fe and Al, the results of the selective precipitation and recovery experiments by pH adjustment, Fe was precipitated and recovered with Magnetite and Goethite at a purity of 74.4% ~ 94.4% at pH 13.0, Al recovered at pH 6.0 could be recovered by precipitation with Gibbsite at a purity of 86.5% ~ 100%.
Finally, as a result of previous experiments, it was thought that selective precipitation and recovery could be possible with high purity precipitate through pH control. Therefore, this verification experiment was applied to the acidic mine drainage of the Ilkwang mine containing a large amount of Fe and Al.
The precipitate of Tank 1 precipitated of controled to pH 4.0 was mixed of Schwertmannite and Ferrihydrite, and the Fe precipitate at a purity of 83.1% was recovered. The precipitate of Tank 2 precipitated of controled to pH 12.0 was separated to precipitation of residual Fe and other heavy metals, and the Al precipitate was re-dissolved. In Tank 3, precipitate was recovered by controled to pH 7.0. However, the recovered precipitate is due to the interference of the suspended precipitate was introduced from Tank 2 such as Al and Fe, Cu, is mixed amorphous precipitate.
In this study, it was confirmed that high purity precipitate can be selectively precipitated and recovered by control the pH of the acid mine drainage dissolved metals. but, research is needed from process of the verification experiment that the migration of suspended sediment between the reactor and the tank is prevented further.