Su Chunming, Ludwig Ralph D
Ground Water and Ecosystems Restoration Division, National Risk Management Research Laboratory, Office of Research and Development, United States Environmental Protection Agency, 919 Kerr Research Drive, Ada, Oklahoma 74820, USA.
Environ Sci Technol. 2005 Aug 15;39(16):6208-16. doi: 10.1021/es050185f.
We investigated a method for delivering ferrous iron into the subsurface to enhance chemical reduction of Cr(VI) in chromite ore processing solid waste (COPSW) derived from the production of ferrochrome alloy. The COPSW is characterized by high pH (8.5-11.5) and high Cr(VI) concentrations in the solid phase (up to 550 mg kg(-1)) and dissolved phase (3-57 mg L(-1)). The dominant solid-phase minerals are forsterite (Mg2SiO4), brucite (Mg-(OH)2), and hydrocalumite [Ca4(Al, Fe)2(OH)12X x 6H2O), X = (OH)2(2-), SO4(2-), CrO4(2-)]. The method utilizes FeSO4 in combination with Na2S2O4 to inhibit oxidation and precipitation of the ferrous iron, thereby preventing well and formation clogging. Laboratory batch tests using a 0.05 M FeSO4 + 0.05 M Na2S2O4 solution indicated effective treatment of both dissolved and solid-phase Cr(VI). Contrary to treatments with FeSO4 and FeCl2 alone, the combination resulted in both complete removal of Cr(VI) from solution and sustained Fe(ll) concentrations in solution after a 24 h period. A field test involving injection of 5700 L of a 0.07 M FeSO4 + 0.07 M Na2S2O4 solution into a COPSW saturated zone (pH 11.5) indicated no well and formation clogging during injection. Examination of a core collected 0.46 m from the injection well following injection indicated effective treatment of the solid phase Cr(VI) based on analysis of water, phosphate solution, and high temperature alkaline extracts. The combined reductant solution also imparted a residual treatment capacity to the COPSW allowing for subsequent treatment of dissolved phase Cr(VI); however, dissemination of the iron in the highly alkaline environment appeared to be impeded by the inability to sufficiently lower the pH with distance from the injection well to avoid precipitation of Fe(OH)2 and likely also FeCO3. Injection of a 0.2 M FeSO4 + 0.2 M Na2S2O4 solution into another COPSW saturated zone (pH 9) indicated much more effective dissemination of the injected iron.
我们研究了一种将亚铁离子输送到地下以增强铬铁矿加工固体废弃物（COPSW，源自铬铁合金生产）中六价铬化学还原的方法。COPSW的特征在于高pH值（8.5 - 11.5）以及固相（高达550毫克/千克）和溶解相（3 - 57毫克/升）中高浓度的六价铬。主要的固相矿物是镁橄榄石（Mg2SiO4）、水镁石（Mg-(OH)2）和水钙铝榴石[Ca4(Al, Fe)2(OH)12X·6H2O，X = (OH)2(2-), SO4(2-), CrO4(2-)]。该方法利用硫酸亚铁与连二亚硫酸钠抑制亚铁离子的氧化和沉淀，从而防止井筒和地层堵塞。使用0.05 M硫酸亚铁 + 0.05 M连二亚硫酸钠溶液进行的实验室批量试验表明，对溶解相和固相六价铬均有有效处理。与单独使用硫酸亚铁和氯化亚铁处理不同，该组合在24小时后既能使溶液中的六价铬完全去除，又能使溶液中亚铁离子浓度保持稳定。一项现场试验涉及向一个COPSW饱和区（pH值11.5）注入5700升0.07 M硫酸亚铁 + 0.07 M连二亚硫酸钠溶液，结果表明注入过程中未出现井筒和地层堵塞。在注入后从注入井0.46米处采集的岩芯分析显示，基于对水、磷酸盐溶液和高温碱性提取物的分析，固相六价铬得到了有效处理。这种组合还原剂溶液还赋予了COPSW剩余处理能力，可用于后续溶解相六价铬的处理；然而，在高碱性环境中铁的扩散似乎受到阻碍，因为无法随着与注入井距离的增加充分降低pH值以避免氢氧化亚铁以及可能的碳酸亚铁沉淀。向另一个COPSW饱和区（pH值9）注入0.2 M硫酸亚铁 + 0.2 M连二亚硫酸钠溶液表明，注入的铁扩散效果要好得多。
