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This study was carried out to develop a selective sequential precipitation process for recovering dissolved metals from acid mine drainages (AMD). The AMD of pH 3 with high concentration of Fe, Al and Mn at the Samma-Teajung coal mine was neutralized by adding neutralizing agents and oxidant to evaluate recovery of the metals and purity of their precipitates. In the case of adding only neutralizing agents, both dissolved Al and Mn were concurrently precipitated at pH 4.5 so that caused the purity of each precipitate to be lowered. However, for neutralization preceded by oxidation of AMD, dissolved metals were removed sequentially in the order of Fe, Al and Mn. Recoveries of dissolved Fe, Al and Mn reached 99.2∼99.3% at pH 4.5, 70.4∼82.2% at pH 5.5, and 37.8∼87.5% at pH 8.5, respectively. Oxidation before neutralization increased the recovery of dissolved Fe and Al in AMD with high purity of precipitates.

The carbonation process, one of the calcium carbonate precipitating methods, consists of a reaction of Ca(OH)2, CO2, and water. In this study, laboratorial tests were conducted to remove the arsenic from the abandoned mine drainage and ground water using the carbonation process. As (III) and As (V) were removed up to 26.5% and 90.6%, respectively in the preliminary test and up to 38.7% and 95.1%, respectively in the second test with an increased amount of hydrated lime. Final pH's of reacted solutions were 6.0 to 6.5, which are satisfying with the water standard and Eh's range between -330 mV and +50 mV. Calcite peak was observed in the reaction precipitates of the follow-up test by XRD analysis and also, hexahedral structures of calcite crystals were identified by SEM analysis. As (III) and As (V) were detected in the range of below 0.04% and 0.06 0.07%, respectively by EDS scanning. Consequently, the carbonation process can remove aqueous As (V) efficiently, but As (III) insufficiently.

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Influence of sulfate on the early hydration in the solidification treatment of abandoned mine tailings was characterized. Solidified specimens using hydrated lime as a binder were prepared with various amounts of added Na 2 SO 4 and different curing days. Unconfined compressive strength measurement, heavy metal leaching test, XRD analysis were performed after 7-, 14-and 28-days curing. According to curing days strength of solidified specimens using only distilled water increased but those with addition of Na 2 SO 4 decreased. External cracks of specimens developed definitely with increasing Na 2 SO 4 concentration and curing days. Concentrations of Cu, Cd, Zn, and As in the leached solutions from solidified specimens decreased significantly but Pb was leached readily in cases of hydrated lime dosage more than 10 wt%. Gypsum and MgSO 4 were identified in the cracked solidified specimens by XRD analysis, and pillar-shaped crystals of SEM image were identified as gypsum in reference with EDS analysis. Crystallization of sulfate in the process of lime-tailing solidification caused cracking, which should be supplemented for solidification treatment of highly sulfur-contained tailing.