Microstructural Analyses of Cr(VI) Speciation in Chromite Ore Processing Residue (COPR)
Microstructural Analyses of Cr(VI) Speciation in Chromite Ore Processing Residue (COPR)
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DOI：
10.1021/es9005338
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发表时间：
2009-07-15
影响因子：
11.4
通讯作者：
Dermatas, Dimitris
中科院分区：
文献类型：
--
作者：
Chrysochoou, Maria;Fakra, Sirine C.;Dermatas, Dimitris
研究了美国两种铬铁矿选矿残渣(COPR)在固相中的形态和分布，这两种残渣分别是灰黑色(GB)颗粒和硬棕色(HB)胶结物。利用显微X射线吸收光谱和显微X射线衍射仪对钴的化学和矿物学进行了研究，并辅之以实验室分析：GB CoN含有总铬(VI)的30%(6000 mg/kg)，是一种以前未见报道的富钠类似物水合铬酸铝钙的大晶体(直径20微米)。这些富铬(VI)相被认为容易受到还原和pH处理的影响。50%以上的铬(VI)赋存于结核中，不易被溶解的还原剂接触，并与富铁的水滑石、水滑石结合，可能还与水镁石结合。这些相在很大的pH范围内是稳定的，因此更难溶解。褐磨石也可能与铬(VI)在结核内部的物理捕获有关。Hb-CoPR不含富铬相，所有铬(VI)弥散在结节内，不存在于胶结基质中，主要结合相为水石榴石和水滑石。从溶解耐酸性、难于接触的铬(VI)化合物的角度来看，HB-COPR的处理是具有挑战性的；同样的情况也适用于GB COPR中类似50%的铬(VI)。
The speciation and distribution of Cr(VI) in the solid phase was investigated for two types of chromite ore processing residue (COPR) found at two deposition sites in the United States: gray-black (GB) granular and hard brown (HB) cemented COPR. COPR chemistry and mineralogy were investigated using micro-X-ray absorption spectroscopy and micro-X-ray diffraction, complemented by laboratory analyses: GB CON contained 30% of its total Cr(VI) (6000 mg/kg) as large crystals (>20 mu m diameter) of a previously unreported Na-rich analog of calcium aluminum chromate hydrates. These Cr(VI)-rich phases are thought to be vulnerable to reductive and pH treatments. More than 50% of the Cr(VI) was located within nodules, not easily accessible to dissolved reductants, and bound to Fe-rich hydrogarnet, hydrotalcite, and possibly brucite. These phases are stable over a large pH range, thus harder to dissolve. Brownmillerite was also likely associated with physical entrapment of Cr(VI) in the interior of nodules. HB COPR contained no Cr(VI)-rich phases; all Cr(VI) was diffuse within the nodules and absent from the cementing matrix, with hydrogarnet and hydrotalcite being the main Cr(VI) binding phases. Treatment of HB COPR is challenging in terms of dissolving the acidity-resistant, inaccessible Cr(VI) compounds; the same applies to similar to 50% of Cr(VI) in GB COPR.