Upgrading the glassy slag from waste disposal by thermal plasma treatment.

The paper reports on the experimental results obtained from the production of glassy slag by the plasma smelting of a mixture of two different wastes. The combination of two wastes with different chemical compositions is a promising way to optimise the energy consumption in the disposal process. Asbestos-cement roof tiles (ACRTs) and fly ash from fluidised-bed boilers (with a weight ratio of 1:1) were used for the preparation of glassy (vitrified) slag. The thermal process facilitated a 14.4% reduction of the weight of the original mixture and a 72% volume reduction of the waste. The glassy slag is then adopted as a raw material in the production of porous materials intended for various architectural applications, thus eliminating the necessity for its further disposal. The formation of a porous glass-ceramic matrix, using the vitrified slag containing CaSO4 as the pore-forming agent, is described in detail. A glass-ceramic foam with 66% porosity is formed by the rapid heating of the mixture of glassy slag and a 1 wt% of CaSO4, consisting of crystallised calcium aluminosilicate (Ca2Al2SiO7, Ca0.88Al1.77Si2.23O8). The thermal conductivity of the prepared porous material, measured by a laser flash thermal analysis, is 0.22 W·m-1·K-1.