Solidification and stabilization of asbestos waste from an automobile brake manufacturing facility using cement

Currently, the generated brake lining waste dust, which contains asbestos a s its major component, is disposed of into a secure landfill without any ad ditional treatment. As an alternative to this, solidification/stabilization (S/S) disposal of the dust was investigated using Portland cement alone ac id Portland cement mixed with activated carbon (AC), as the binders. Toxici ty Characteristics Leaching procedure (TCLP) results on the solidified matr ix 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 4-2 4% compared to cement alone. The pH of the TCLP leachate extracted from vir gin 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 TCL P extract for the untreated dust. Results of ANS 10.1 (modified) leach prot ocol revealed that Ba in cement-treated samples showed the highest leach ra te, followed by Zn, Pb, Cr, Cu and Fe. The leach rate of heavy metals decre ased with progress in time. Cement mixed with AC exhibited similar leach ch aracteristics, however, the leach rate was lower. The linear relationship b etween the cumulative fraction leached (CFL) and the square root of leachin g time in all cement-based samples indicate that a diffusional process is t he controlling transport mechanism for the leaching of the heavy metals. Th e 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 w ell 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, w hich was well above the specified limit of 414 kPa for such matrices. An ec onomic 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 effect ively immobilized the heavy metals of concern, cost considerations may hind er the commercial adaptation of this technique for waste disposal unless ne w regulatory demands are implemented. (C) 2000 Elsevier Science B.V. All ri ghts reserved.