Mineral Carbonation Using Asbestos-Containing Cement Board Waste

Mineral carbonation appears to be one of the plausible methods for the practical fixation of CO2. Carbon consumption and sequestration by carbonation reactions involving alkaline elements such as Ca and Mg have been developed. Suitable feedstocks for CO2 sequestration are mineral carbonation using Ca/Mg-silicates. Asbestos-containing cement board waste consists of chrysotile asbestos which is one of the Mg-silicate and cement. Chrysotile is one of the raw materials to form carbonate mineral for CO2 fixation in previous studies and cement contains a quantity of calcium which is able to react with CO2. Generally, asbestos-containing cement board waste is dumped in controlled waste sites in South Korea. However, this cannot be regarded as an ultimate solution because dispersion of asbestos fibers in the air is an intrinsic risk during dumping operations and in the long-term management. An alternative solution is thermal transformation of asbestos-containing material into non-hazardous phase. Therefore, the aims of the study were to sequester CO2 using asbestos-containing cement board waste via mineral carbonation and to detoxify chrysotile asbestos in cement board waste via heat treatment. Two steps of experiments were designed: (1) synthesis of a carbonate mineral (i.e., calcite and magnesite), via the physicochemical reactions of fragmented cement board with CO2 and (2) transformation of fibrous asbestos into non-fibrous material through heat treatment. Physicochemical and mineralogical properties of cement board waste were investigated by TG-DTA , XRF, XRD, SEM, and EDS analyses. XRD analysis showed that the calcite (CaCO3) was formed after reaction of fragmented cement board with CO2. Mineralogical characteristics showed minerals such as chrysotile [Mg3Si2O5(OH)4] and calcite (CaCO3) in the reactions of fragmented cement board with CO2 were transformed into calcite (CaCO3), calcium oxide (CaO), and quartz (SiO2) by heat treatment. SEM-EDS analyses showed that chrysotile fibers were disappeared from cement board. These results indicate that thermal treatment of asbestos-containing cement board combined with physicochemical reactions with CO2 can detoxify chrysotile asbestos in cement board waste and fix CO2 by forming carbonate mineral.