Solidification and stabilization of asbestos brake lining dust using polymeric resins

Two polymeric resins, Polymal and Hetron, were evaluated to solidify/stabil ize (S/S) for ultimate disposal brake lining dust containing asbestos. This dust was generated as part of a sequence of processing steps in the manufa cture of automobile brake linings. The mean grain size of the lining dust f or disposal was 298.2 mu m, the range being from 24.9 to 567.3 mu m. Based on the Toxicity Characteristic Leachability Procedure (TCLP) and the Americ an Nuclear Society (ANS) 16.1 (modified) leach protocols, although the untr eated lining dust contained high concentrations of Zn, Ba, Pb, Fe, Cu, and Cr, solidification with Polymal and Hetron respectively reduced the leachab le fraction of these heavy metals in the lining dust to less than 14 and 18 %, compared to untreated control; and the heavy metal concentrations in the TCLP leachate were below the permissible limits set by the Malaysia Enviro nmental Quality Act (EQA) (1974), the Environment Quality (Sewage and Indus trial Effluents) Regulations (1979), as well as the USEPA regulatory limit fur TCLP. The final pH of the extract from the untreated dust ranged from 4 .92 to 4.95, whereas when polymeric resins were used, the pH increased to b etween 5.1 and 5.2. When the ANS 16.1 (modified) leach test was performed, the leaching rate was highest for Zn, followed by Ba and Pb, while the leac hing of Cr, Cu, and Fe was too low for detection. The observed linear relat ionship between the cumulative fraction leached (CFL) and the square root o f the leaching time in all polymer resin treated samples indicates that the mechanism of leaching is mainly through diffusion. The Leachability Index (Li) obtained ranged between 9 and 10, which exceeds the guidance value of 6, clearly indicating that the heavy metal retention within the solidified matrix is quite effective. The hardening time when polymeric resins were us ed ranged anywhere from 1.5 to 12 h, and this decreased as the amount of ME K Peroxide initiator was increased. Compressive strength of the brake linin g solid matrix was between 53 and 68 MPa, which was much higher than the st andard guidance limit for polymeric resin solidification. Between the two r esins, Polymal shows better performance in terms of heavy metal retention c apability, whereas Hetron exhibits higher compressive strength. Despite the attractive performance features of either of the resins, S/S with either o f them appears to be prohibitively expensive for the current Malaysian regu latory marketplace, although attractive elsewhere.