Case Studies in Chemical and Environmental Engineering (Dec 2023)
Thermodynamic prediction of the possibility of comprehensive processing chrysotile-asbestos waste
Abstract
The article presents the results of thermodynamic prediction of a new process of interaction of chrysotile-asbestos waste with calcium carbide and aluminium (III) oxide with the co-producing gaseous magnesium and calcium aluminosilicate. The study was carried out by the thermodynamic modelling method using the HSC-6.0 Chemistry software package developed by the Finnish metallurgical company Outokumpu, and the optimal parameters of the process under study were determined by means of the second-order rotatable experiment planning designs with the computer construction of a 3D model of changing the technological parameters. Based on the results obtained, it was established that the interaction products in the system under consideration are Mg(g), CaSiO3, 2CaO·Al2O3·SiO2, FeSi, SiC, SiO(g), Fe, Fe3Si, CO(g). The equilibrium distribution degree of the elements in the system is largely dependent on temperature and calcium carbide, which, from a thermodynamic point of view, is more reactive to MgO than FeSi2. An increase in the calcium carbide content in the charge reduces the transition degrees of calcium and silicon into the silicates (2CaO·Al2O3·SiO2 and CaSiO3), increases the transition degrees of aluminium into 2CaO·Al2O3·SiO2 and silicon into SiC and SiO(g). Up to 1640 °C, an increase in the amount of calcium carbide reduces the transition of silicon into the alloy, and at the higher temperature, on the contrary, it increases. In the temperature range of 1636–1700 °C at a pressure of 0.1 bar, to achieve high extraction degrees of the elements from the chrysotile-asbestos production waste, such as 80.0–90.6% of magnesium into gas, 80–84.3% of calcium, 74.3–76.8% of silicon and 81,6-87,4% of aluminium into the silicate melt, the process should be carried out in the presence of 28–31.5% of calcium carbide. Silicon, passing to a small extent into the alloy, forms nickel-alloyed (2.8–3.1% of Ni) FeSi25 ferrosilicon. The silicate melt mainly consists of 2CaO∙Al2O3·SiO2 (72,9%) and CaSiO3 (10.6%).
