The carbonation of chrysotile [Mg₃Si₂O₅(OH)₄] was studied at various temperatures in order to examine the carbonation rate and Mg leaching properties in an alkali solution and distilled water using the direct method. For the efficient carbonation reaction, the chrysotile was converted to metachrysotile by heating at 630°C for 2 h. The carbonation rate was found to increase with the reaction temperature: 5 and 31% at 100°C and 45 and 53% at 260°C in distilled water and alkali solution, respectively. The carbonation in the alkali solution was faster producing well-faceted rhombohedral magnesite (MgCO₃) in comparision to the case in the distilled water. Highly crystalline magnesite could be obtained after the carbonation for 1 h at 260°C under a CO₂ pressure of 3 MPa in the alkali solution.
The additional object of this study was to convert the fibrous chrysotile to a non-hazardous material. During carbonation, the magnesite exhibited the typical rhombohedral morphology while the unreacted chrysotile changed primarily to aggregations of chrysotile crystals. This result has an important implication for the elimination of toxicity through the transformation of chrysotile asbestos into a non-hazardous material.