(General session) Mineral processing / Environment［Wed. Sep 13, 2023 AM Room-6］

[2601-08-06] Zinc incorporation with bio-birnessite in a passive treatment plant: mechanisms and implications

○Sereyroith Tum¹, Naoyuki Miyata², Taiki Katayama¹, Miho Watanabe², Yohey Hashimoto³, Tetsuo Yasutaka¹ (1. Institute for Geo-Resources and Environment, Geological Survey of Japan, National Institute of Advanced Industrial Science and Technology , 2. Department of Biological Environment, Akita Prefectural University, 3. Department of Bioapplications and Systems Engineering (BASE), Tokyo University of Agriculture and Technology)

Chairperson: Kazunori Nakashima (Hokkaido University)

Keywords:passive-treatment , bio-birnessite, reaction transport , sludge

To reduce the cost of acid mine drainage (AMD) treatment, a pilot-scale passive treatment was implemented to investigate the removal efficiency of zinc (Zn) and manganese (Mn) under circumneutral conditions (pH 6.5-7.5). Dissolved Mn was removed from the AMD through oxidation and precipitation mechanisms involving Mn-oxidizing bacteria, resulting in the formation of bio-birnessite. Zn was expected to incorporate with bio-birnessite. However, the actual removal mechanisms have not yet been determined. Therefore, the objectives of this study were (1) to understand the zinc removal mechanisms in the passive treatment plant and (2) to determine the future implications of zinc removal from AMD using bio-birnessite.
The sludge precipitated in the passive treatment and treated water were collected for further analysis. Sludge mineralogy and chemical composition were analyzed using X-ray diffraction (XRD), X-ray fluorescence, and scanning electron microscopy with energy-dispersive X-ray spectroscopy. Selective sequential extraction was implemented to determine the quantity of Zn incorporation with bio-birnessite. Water chemistry and aqueous solutions were determined using inductively coupled plasma mass spectrometry. The kinetic reaction transport model of Mn and Zn was obtained to optimize the future implications of the passive treatment using Phreeqc.
The results indicated sludge contained Zn about 18%, which bounded to the bio-birnessite structure as a result of surface complexation and coprecipitation. Woodruffite was detected in the XRD pattern of the sludge, indicating the coprecipitation of Zn and bio-birnessite. The kinetic reaction transport model suggested that the passive treatment plant potentially treated Zn and Mn within a study hydraulic retention time (HRT) of 1 day. In the passive treatment, Zn alone cannot be treated without the presence of Mn and Mn-oxidizing bacteria in the system. The formation of bio-birnessite plays a major role in the Zn and Mn removal mechanisms in the passive treatment process.