Moon Deok Hyun, Wazne Mahmoud, Jagupilla Santhi Chandra, Christodoulatos Christos, Kim Min Gyu, Koutsospyros Agamemnon
Center for Environmental Systems, Stevens Institute of Technology, Hoboken, NJ 07030, USA.
Sci Total Environ. 2008 Jul 25;399(1-3):2-10. doi: 10.1016/j.scitotenv.2008.03.040. Epub 2008 May 16.
A long-term bench scale treatability study was performed to assess the ability to remediate chromite ore processing residue (COPR) using calcium polysulfide (CaS(5)). COPR materials were characterized with respect to particle size, pH, curing period and mineralogy. A stoichiometric ratio of sulfide species to hexavalent chromium (Cr(6+)) of 2 was used for the long-term treatment of COPR. The effectiveness of CaS(5) treatment was assessed using the toxicity characteristic leaching procedure (TCLP), alkaline digestion, and X-ray absorption near edge structure (XANES) analyses. The formation of ettringite, known as a heaving agent, was investigated following the treatment of CaS(5), using X-ray powder diffraction (XRPD) and scanning electron microscopy (SEM) along with an energy dispersive X-ray spectroscopy (EDX). Overall, after a curing period of 18 months, the TCLP total chromium (Cr) and alkaline digestion (Cr(6+)) results obtained from the treatability study showed that the concentrations were lower than 5 mg L(-1) and 9 mg kg(-1), respectively. However, XANES results obtained from samples cured for 18 months showed that all of the treated samples had higher Cr(6+) concentrations than shown using alkaline digestion. The lowest XANES Cr(6+) concentration of 610.2 mg kg(-1) was obtained from the sample with a particle size less than 0.075 mm and a pH value of 9. Particle size reduction prior to the addition of the reductant, along with pH reduction was found to be strongly associated with the treatment performance. Ettringite formation, due to pH increase over time in the samples, where the initial pH was adjusted to 9, was verified by XRPD and SEM-EDX analyses, indicating that a pH less than 9 should be maintained to avoid ettringite formation.
进行了一项长期的实验室规模可处理性研究，以评估使用多硫化钙（CaS₅）修复铬铁矿加工残渣（COPR）的能力。对COPR材料的粒度、pH值、养护期和矿物学进行了表征。在对COPR进行长期处理时，硫化物与六价铬（Cr(6+)）的化学计量比为2。使用毒性特性浸出程序（TCLP）、碱性消解和X射线吸收近边结构（XANES）分析评估了CaS₅处理的有效性。使用X射线粉末衍射（XRPD）、扫描电子显微镜（SEM）以及能量色散X射线光谱（EDX），研究了CaS₅处理后被称为膨胀剂的钙矾石的形成。总体而言，经过18个月的养护期后，可处理性研究获得的TCLP总铬（Cr）和碱性消解（Cr(6+)）结果表明，浓度分别低于5 mg L⁻¹和9 mg kg⁻¹。然而，从养护18个月的样品中获得的XANES结果表明，所有处理过的样品的Cr(6+)浓度都高于碱性消解显示的浓度。从粒度小于0.075 mm且pH值为9的样品中获得的最低XANES Cr(6+)浓度为610.2 mg kg⁻¹。发现在添加还原剂之前减小粒度以及降低pH值与处理性能密切相关。通过XRPD和SEM-EDX分析证实，由于样品中pH值随时间升高（初始pH值调整为9）而形成了钙矾石，这表明应将pH值维持在9以下以避免钙矾石的形成。
