Chan Y M, Agamuthu P, Mahalingam R
Institute of Postgraduate Studies and Research, University of Malaya, 50603, Kuala Lumpur, Malaysia.
J Hazard Mater. 2000 Oct 2;77(1-3):209-26. doi: 10.1016/s0304-3894(00)00244-2.
Currently, the generated brake lining waste dust, which contains asbestos as its major component, is disposed of into a secure landfill without any additional treatment. As an alternative to this, solidification/stabilization (S/S) disposal of the dust was investigated using Portland cement alone and Portland cement mixed with activated carbon (AC), as the binders. Toxicity Characteristics Leaching Procedure (TCLP) results on the solidified matrix showed that cement was able to immobilize the heavy metals, Ba, Zn, Cr, Pb, Cu and Fe, to within the limits set by the US EPA for TCLP. Addition of AC to the cement reduced the leaching of heavy metals by an additional 4-24% compared to cement alone. The pH of the TCLP leachate extracted from virgin cement, and from dust treated with cement with or without AC was found to increase to 10.9-12.5 as opposed to an initial value of 4.93 for the TCLP extract for the untreated dust. Results of ANS 16.1 (modified) leach protocol revealed that Ba in cement-treated samples showed the highest leach rate, followed by Zn, Pb, Cr, Cu and Fe. The leach rate of heavy metals decreased with progress in time. Cement mixed with AC exhibited similar leach characteristics, however, the leach rate was lower. The linear relationship between the cumulative fraction leached (CFL) and the square root of leaching time in all cement-based samples indicate that a diffusional process is the controlling transport mechanism for the leaching of the heavy metals. The obtained Leachability Indices (L(i)) of 7.6-9.1 and 8.3-9.5 for cement and cement with AC, respectively, were low but exceeded the guidance value of 6, which clearly indicates that all the heavy metals studied are retained well within solid matrices. Cement-based S/S hardening times increased from 30 to 96 h as the dust content increased from 40 to 70 wt.%. The resulting solid matrices exhibited a compressive strength ranging from 1 to 12 MPa, which was well above the specified limit of 414 kPa for such matrices. An economic analysis indicates that the disposal costs for the dust in the only available secure landfill would increase by 40.3% if one were to go for the cement S/S option. Addition of AC to the cement would escalate this by an additional 43.8%. Although the S/S of brake lining dust using cement effectively immobilized the heavy metals of concern, cost considerations may hinder the commercial adaptation of this technique for waste disposal unless new regulatory demands are implemented.
目前，产生的制动衬片废粉尘以石棉为主要成分，未经任何额外处理便被处置到安全填埋场。作为替代方案，研究了仅使用波特兰水泥以及波特兰水泥与活性炭（AC）混合作为粘结剂对粉尘进行固化/稳定化（S/S）处置。对固化体进行的毒性特征浸出程序（TCLP）结果表明，水泥能够将重金属钡、锌、铬、铅、铜和铁固定在美国环保署（US EPA）规定的TCLP限值范围内。与仅使用水泥相比，向水泥中添加AC可使重金属的浸出量再降低4 - 24%。从未经处理的水泥、以及用含或不含AC的水泥处理过的粉尘中提取的TCLP浸出液的pH值从未经处理粉尘的TCLP提取物的初始值4.93增加到了10.9 - 12.5。ANS 16.1（修订版）浸出协议的结果显示，水泥处理样品中的钡浸出率最高，其次是锌、铅、铬、铜和铁。重金属的浸出率随时间推移而降低。水泥与AC混合后的浸出特性相似，不过浸出率更低。所有水泥基样品中浸出累积分数（CFL）与浸出时间平方根之间的线性关系表明，扩散过程是重金属浸出的控制传输机制。分别测得水泥和含AC水泥的浸出性指数（L(i)）为7.6 - 9.1和8.3 - 9.5，数值较低但超过了指导值6，这清楚地表明所有研究的重金属在固体基质中保留良好。随着粉尘含量从40 wt.%增加到70 wt.%，水泥基S/S硬化时间从30小时增加到96小时。所得固体基质的抗压强度范围为1至12 MPa，远高于此类基质规定的414 kPa限值。经济分析表明，如果选择水泥S/S处置方案，唯一可用的安全填埋场中粉尘的处置成本将增加40.3%。向水泥中添加AC会使成本再额外增加43.8%。尽管使用水泥对制动衬片粉尘进行S/S处置有效地固定了相关重金属，但成本因素可能会阻碍该技术在废物处置方面的商业应用，除非实施新的监管要求。
