Microbial communities in constituent layers of a geosynthetic clay-liner cover system and underlying tailings at the abandoned Cu/Zn Kam Kotia Mine (ON, Canada)

Sustainable mine-waste management practices are an increasingly important aspect of metal production. Canada is home to more than 10,000 orphaned and abandoned mine sites, the legacy of which continues to impact local environments and communities. The largest liability associated with the metal-mining industry derives from acid mine drainage (AMD), caused by accelerated chemical and/or biological oxidation of sulfidic minerals within waste rock and mill tailings. AMD is characterized by acidic water, containing high concentrations of sulfate, ferrous iron, and associated metal(loid)s. The abandoned Cu/Zn Kam Kotia Mine, near Timmins, Ontario, is undergoing remediation by the Province of Ontario. Installation of a geosynthetic clay-liner (GCL) cover system was completed in 2008 to isolate acid-generating tailings from water and oxygen to mitigate sulfide oxidation. The GCL cover system is comprised of a vegetated soil cover layer, a granular protective layer (sand), a clay moisture retaining layer (clay), a GCL, granular capillary-break material (cushion sand), and a crushed waste-rock capillary-break layer, overlaying the acid-generating tailings. The goal of this study is to characterize the microbiology of the cover system and the underlying tailings to assess the performance of the cover for mitigating AMD generation. Total genomic DNA was extracted from each layer of the cover system, as well as the underlying tailings, and was analysed using a high-throughput amplicon sequencing of the 16S rRNA gene. Low relative abundances (and also viable counts) of microorganisms that catalyze transformations of iron and sulfur in the covered tailings, compared to previous studies on unreclaimed tailings, indicate that sulfide oxidation rates have decreased due to the presence of the GCL.

矿山废弃物可持续管理实践已成为金属生产领域日益重要的组成部分。加拿大拥有超过10000座无主废弃矿山，其遗留影响至今仍持续波及当地环境与社区。金属采矿行业最突出的环境隐患源于酸性矿山排水（AMD）——该现象由废石与选矿尾矿中硫化矿物的加速化学及/或生物氧化作用引发。酸性矿山排水以富含高浓度硫酸盐、亚铁离子及相关金属/类金属的酸性水体为典型特征。位于安大略省蒂明斯附近的废弃铜锌（Cu/Zn）卡科蒂亚（Kam Kotia）矿山目前正由安大略省实施修复工程。该项目于2008年完成合成黏土衬层（GCL）覆盖系统的安装，旨在隔绝产酸尾矿与水、氧气的接触，以减缓硫化物的氧化过程。这套GCL覆盖系统覆于产酸尾矿之上，由植被土层、粒状保护层（砂层）、黏土保水层（黏土层）、GCL衬层、粒状防毛细管材料（垫层砂）以及破碎废石防毛细管层构成。本研究的核心目标是解析该覆盖系统及其下方尾矿的微生物群落特征，以此评估该覆盖系统在减缓酸性矿山排水生成方面的效能。研究人员从覆盖系统的各分层及下方尾矿中提取总基因组DNA，通过16S rRNA基因高通量扩增子测序技术开展分析。与此前针对未修复尾矿的相关研究相比，本研究中覆盖尾矿内催化铁、硫转化的微生物相对丰度（及活菌计数）均处于较低水平，这表明GCL的存在已使硫化物氧化速率有所降低。