Geelhoed Jeanine S, Meeussen Johannes C L, Roe Martin J, Hillier Stephen, Thomas Rhodri P, Farmer John G, Paterson Edward
The Macaulay Institute, Craigiebuckler, Aberdeen, AB 8QH, UK.
Environ Sci Technol. 2003 Jul 15;37(14):3206-13. doi: 10.1021/es0264798.
Chromite ore processing residue (COPR), derived from the so-called high lime processing of chromite ore, contains high levels of Cr(III) and Cr(VI) and has a pH between 11 and 12. Ferrous sulfate, which is used for remediation of Cr(VI) contamination in wastewater and soils via reduction to Cr(III) and subsequent precipitation of iron(III)/chromium(III) hydroxide, has also been proposed for remediation of Cr(VI) in COPR. Instead, however, addition of FeSO4 to the infiltrating solution in column experiments with COPR greatly increased leaching of Cr(VI). Leached Cr(VI) increased from 3.8 to 12.3 mmol kg(-1) COPR in 25 pore volumes with 20 mM FeSO4, reaching solution concentrations as high as 1.6 mM. Fe(II) was ineffective in reducing Cr(VI) to Cr(III) because it precipitated when it entered the column due to the high pH of COPR, while Cr(VI) in solution was transported away with the infiltrating solution. The large increase in leaching of Cr(VI) upon infiltration of sulfate, either as FeSO4 or Na2SO4, was caused by anion exchange of sulfate for chromate in the layered double hydroxide mineral hydrocalumite, a process for which scanning electron microscopy with energy-dispersive X-ray microanalysis provided direct evidence.
铬铁矿加工残渣（COPR）源自铬铁矿的所谓高钙加工，含有高浓度的Cr（III）和Cr（VI），pH值在11至12之间。硫酸亚铁可通过将废水中和土壤中的Cr（VI）还原为Cr（III）并随后沉淀出铁（III）/铬（III）氢氧化物来修复Cr（VI）污染，也有人提议用它来修复COPR中的Cr（VI）。然而，在对COPR进行的柱实验中，向渗透溶液中添加FeSO4却大大增加了Cr（VI）的浸出量。在25个孔隙体积中加入20 mM FeSO4后，浸出的Cr（VI）从3.8 mmol kg（-1）COPR增加到12.3 mmol kg（-1）COPR，溶液浓度高达1.6 mM。Fe（II）无法将Cr（VI）还原为Cr（III），因为由于COPR的高pH值，它进入柱体时就会沉淀，而溶液中的Cr（VI）则随渗透溶液被带走。无论是以FeSO4还是Na2SO4形式存在的硫酸盐渗透后，Cr（VI）浸出量的大幅增加是由层状双氢氧化物矿物水钙铝榴石中硫酸根与铬酸根的阴离子交换引起的，扫描电子显微镜结合能量色散X射线微分析为这一过程提供了直接证据。
