Department of Environmental Science, University of Arizona, 1177 E 4th St, Shantz 429, Tucson, AZ, 85721, USA.
Department of Environmental Engineering, Southwest Jiaotong University, Chengdu, 610031, China.
Environ Sci Pollut Res Int. 2021 Sep;28(33):45519-45533. doi: 10.1007/s11356-021-13869-8. Epub 2021 Apr 18.
Treatment of aqueous leachate from acid mine tailings with pristine biochar (BC) resulted in the removal of more than 90% of the dissolved arsenic with an attendant rapid and sustained pH buffering from 3 to 4. Pine forest waste BC was transformed to a highly effective adsorbent for arsenic remediation of acid mine drainage (AMD) because the dissolved iron induced "activation" of BC through accumulation of highly reactive ferric hydroxide surface sites. Physicochemical properties of the BC surface, and molecular mechanisms of Fe, S, and As phase transfer, were investigated using a multi-method, micro-scale approach (SEM, XRD, FTIR, XANES, EXAFS, and STXM). Co-located carbon and iron analysis with STXM indicated preferential iron neo-precipitates at carboxylic BC surface sites. Iron and arsenic X-ray spectroscopy showed an initial precipitation of ferrihydrite on BC, with concurrent adsorption/coprecipitation of arsenate. The molecular mechanism of arsenic removal involved bidentate, binuclear inner-sphere complexation of arsenate at the surfaces of pioneering ferric precipitates. Nucleation and crystal growth of ferrihydrite and goethite were observed after 1 h of reaction. The high sulfate activity in AMD promoted schwertmannite precipitation beginning at 6 h of reaction. At reaction times beyond 6 h, goethite and schwertmannite accumulated at the expense of ferrihydrite. Results indicate that the highly functionalized surface of BC acts as a scaffolding for the precipitation and activation of positively charged ferric hydroxy(sulf)oxide surface sites from iron-rich AMD, which then complex oxyanion arsenate, effectively removing it from porewaters. Graphical abstract.
用原始生物炭（BC）处理酸性矿山尾矿水浸出液，可去除超过 90%的溶解砷，同时将 pH 值从 3 迅速且持续缓冲至 4。松林废 BC 转化为一种非常有效的酸性矿山排水（AMD）砷修复吸附剂，因为溶解铁通过积累高反应性的氢氧化铁表面位而引起“激活”BC。使用多方法、微观尺度方法（SEM、XRD、FTIR、XANES、EXAFS 和 STXM）研究了 BC 表面的物理化学性质和 Fe、S 和 As 相转移的分子机制。与 STXM 共定位的碳和铁分析表明，在羧酸 BC 表面位优先形成新形成的铁。铁和砷 X 射线光谱表明，BC 上最初沉淀出水铁矿，同时吸附/共沉淀砷酸盐。砷去除的分子机制涉及砷酸盐在先驱铁沉淀物表面的双齿、双核内配位络合。反应 1 h 后观察到水铁矿和针铁矿的成核和晶体生长。AMD 中的高硫酸盐活性在反应 6 h 时开始促进水羟铁锰矿沉淀。在 6 h 以上的反应时间内，针铁矿和水羟铁锰矿的积累以牺牲水铁矿为代价。结果表明，BC 的高功能化表面充当支架，用于从富含铁的 AMD 中沉淀和激活带正电荷的铁羟基（硫）氧化物表面位，然后与含氧阴离子砷酸盐络合，有效地将其从孔隙水中去除。
