A NOVEL REMEDIATION METHOD LEARNT FROM NATURAL ATTENUATION PROCESS FOR Cu- AND Zn-BEARING WASTEWATER(2010 TMC Special Paper)

To develop a novel remediation for Cu- and Zn-bearing wastewater, the natural attenuation process in Dougamaru abandoned mine at Shimane Prefecture, Japan was investigated. In the Dougamaru abandoned mine, Cu- and Zn-bearing mine drainage was naturally attenuated by formation of green precipitate composed of Cu-bearing layered double hydroxide (LDH), hydrowoodwardite (HW) with chemical formula such as Cu_<0.66>Zn_<0.09>Fe_<0.01>Al_<0.23>(OH)_2(SO_4)_<0.15>・mH_2O. This attenuation was achieved at pH 6.0 with aeration and bacterial respiration and without any neutralization process attributed to the mixing with spring or surface water. The formation of the HW at pH 6 is also confirmed by thermodynamic consideration in this study. The formation process of the HW at the Dougamaru abandoned mine teaches us a novel technology for remediation system with addition of Al ion to wastewater and without employing any extensive chemical treatment processes. From the experiment to check applicability of Cu- and Zn-bearing LDHs to wastewater treatment, HW (Cu-bearing LDH) and zincowoodwardite (ZW; Zn-bearing LDH) were obtained by addition of Al ion to the Cu- and Zn-bearing wastewater from lower pH condition. The improvement of removal efficiency by adding Al ion in Cu-bearing wastewater system was not so clear in the experiment because Cu ion is removed from the synthetic wastewater due to Cu-hydroxyl sulfate precipitation at the experimental condition. On the other hand, the removal efficiencies of Zn ion showed the range from 0 to 30% even at pH 6.0 and improved with increasing initial Al ion content. The experimental results in Zn-bearing wastewater system indicate that the safety remediation of Zn ion can be achieved even at lower pH than 6.0-7.0 by selection of the ZW as a candidate of the solubility-limiting solid phase. Moreover, because of high anion exchange capacity of LDH, the method with addition of Al ion source for the wastewater treatment may also be useful for the treatment of wastewater containing Cu and Zn ions and simultaneously with As, Se, and Sb anions, which shows good performance in terms of anion remediation.