Dermatas Dimitris, Chrysochoou Maria, Moon Deok Hyun, Grubb Dennis G, Wazne Mahmoud, Christodoulatos Christos
W.M. Keck Geoenvironmental Laboratory, Center for Environmental Systems, Stevens Institute of Technology, Hoboken, New Jersey 07030, USA.
Environ Sci Technol. 2006 Sep 15;40(18):5786-92. doi: 10.1021/es0604461.
A pilot-scale treatment study was implemented at a deposition site of chromite ore processing residue (COPR) in New Jersey. Ferrous sulfate heptahydrate (FeSO4 x 7H2O) was employed to reduce hexavalent chromium in two dosages with three types of soil mixing equipment. XANES analyses of treated samples cured for 240 days indicated that all treatment combinations failed to meet the Cr(VI) regulatory limit of 240 mg/kg. More importantly, the discrepancy between XANES and alkaline digestion results renders the latter unreliable for regulatory purposes when applied to ferrous-treated COPR. Regardless of Cr-(VI), the introduction of reductant containing sulfate, mechanical mixing, water, acidity, and the resulting temperature increase in treated COPR promoted dissolution of brownmillerite (Ca2FeAlO5), releasing alumina and alkalinity. The pH increase caused initially precipitated gypsum (CaSO4 x 2H2O) to progressively convert to ettringite (Ca6Al2(SO4)3 x 32H2O) and its associated volume expansion under both in situ and ex situ conditions, with a maximum of 0.8 m vertical swell within 40 days of curing. While Cr-(VI) treatment remains a challenge, the intentional exhaustion of the heave potential of COPR by transforming all Al sources to ettringite emerges as a possible solution to delayed ettringite formation, which would hamper site redevelopment.
在新泽西州的一个铬铁矿加工残渣（COPR）沉积场地进行了中试规模的处理研究。使用七水硫酸亚铁（FeSO₄·7H₂O）以两种剂量与三种类型的土壤混合设备来还原六价铬。对养护240天的处理后样品进行的X射线吸收近边结构（XANES）分析表明，所有处理组合均未达到240毫克/千克的六价铬监管限值。更重要的是，当应用于经亚铁处理的COPR时，XANES与碱性消解结果之间的差异使得碱性消解结果在监管目的方面不可靠。无论六价铬情况如何，在经处理的COPR中引入含硫酸盐的还原剂、机械混合、水、酸度以及由此导致的温度升高，都会促进钙铁黄长石（Ca₂FeAlO₅）的溶解，释放出氧化铝和碱度。pH值的升高导致最初沉淀的石膏（CaSO₄·2H₂O）逐渐转化为钙矾石（Ca₆Al₂(SO₄)₃·32H₂O），并且在原位和异位条件下都会伴随其相关的体积膨胀，在养护40天内垂直膨胀最大可达0.8米。虽然六价铬处理仍然是一个挑战，但通过将所有铝源转化为钙矾石来有意耗尽COPR的膨胀潜力，似乎是解决钙矾石延迟形成问题的一种可能方案，否则会阻碍场地再开发。
