Indian Journal of Chemical Technology Vol. 22, May-July 2015, pp. 162-166 Notes Immobilization of toxic metals of industrial waste via low temperature vitrification I B Singh* & K Chaturvedi CSIR-Advanced Materials and Processes Research Institute, Bhopal 462 064 (M.P.), India E-mail: ibsingh58@yahoo.com Received 14 March 2014; accepted 23 May 2014 Wastes generated from metal finishing and galvanizing processes, have been vitrified at 800-950°C after heating of waste, clay and sodium carbonate in their different proportions. Observed results indicate that a composition containing 1:1:2 ratio of waste, sodium carbonate and clay attains a clear vitrification at 950°C. TCLP analysis of the leachates obtained from the vitrified masses of different wastes indicates the leachability of Cr, Cu, Zn and Pb becomes far below from their threshold values. Decrease of waste content and increase of sodium carbonate in the mixture has shown a further decrease of vitrification temperature. However, compressive strength of the vitrified mass is found to reduce considerably with the increase of sodium carbonate content in the vitrifying compositions. Keywords: Hazardous waste, Leachbility, TCLP, Toxic metals, Vitrification Fast industrialization has resulted in generation of a large amount of toxic metals like Cr, Pb, Cu, Zn, etc bearing hazardous waste from the metal finishing, electroplating and galvanizing processes. Disposal of such types of waste in the soil causes contamination of ground and surface water. Because physical and chemical changes due to weathering or other effects start the release of contaminates from the waste that percolate in to the water. To control leaching of toxic elements from waste, thermal treatment is known to decrease the mobility of the toxic metals with the increase of thermal treatment temperature 1-5 . Thermal treatment approaches like vitrification, sintering, bricks firing, etc are being employed for stabilization and solidification of the wastes. Among them, vitrification is considered to be promising one as contaminants get imbedded/immobilized in to the glassy structure of the vitrified mass that reduces the susceptibility of their release in the environment. Kox and Vlist 6 have carried out vitrification at >1650°C in year 1980 itself for the treatment of metals bearing hydroxide of the plating waste. Later on, a number of studies have been carried for the thermal treatment of industrial metals bearing hazardous wastes via vitrification process. Thermal treatment of electroplating sludge containing Cr with/without bottom ash via vitrification at ~1300°C, has been found to retain more than 98% Cr of the waste in the vitrified slag 7 . Heavy metals like Cr, Ni, Cu, Zn, Pb of galvanic waste have been immobilised using soda-lime-borosilicate glass via vitrification at ~1300°C 8 . In vitrification of stainless dust with silica- clay mixture at 1100°C, it was observed that hazardous components of the waste get entrapped into the amorphous silica-alumina-clay vitrified matrix 9 . Addition of silica/clay/alumina plays a major role in making of amorphous matrix after vitrification. Silica (SiO 2 ) addition is beneficial on the immobilization of hazardous metals and the encapsulation of a glass network during the vitrification process 10,11 . Invention related to treatment of radioactive and/or hazardous waste by making silicate-based glass after heating at 1150°C has revealed entrapping of toxic elements of the waste in to the glassy structure 12 . Another invention describes the treatment of contaminated soil containing stainless steel dust via vitrification at 1450°C 13 . However, involvement of a higher thermal energy for attaining vitrification at high temperature (~1400°C), makes this process very expensive. In addition, some of the components of the waste get vaporized at this range of temperature, create secondary pollution problem in the environment. This is another major disadvantages of vitrification at high temperature. To reduce cost and minimize formation of toxic vapours, attainment of vitrification at lower temperature (<1000°C) could be a viable thermal treatment technology for the immobilization of toxic metals of industrial hazardous wastes. In view this, present investigation was aimed to develop low temperature eutectic composition containing waste, clay/fly ash and sodium carbonate (Na 2 CO 3 ) in their different proportions to obtain vitrification at <1000°C. Determination of leachabilty of different metals of the waste from the vitrified masses, was another objective of the study to examine the extent of the immobilization of the toxic metals of the waste in the vitrified matrix.