In situ laboratory X-ray powder diffraction study of wollastonite carbonation using a high-pressure stage

A high-pressure gas stage, recently developed for in-situ X-ray powder diffraction studies of polymer crystallization under CO_2, has been used to observe the carbonation of wollastonite under various temperature/pressure conditions despite the fact that the stage was not designed for use with moisture-containing samples. The rate of carbonation of wollastonite at 60 °C was found to be pressure-independent. Additional experiments at 34.5 bar between 43 and 73 °C enabled an activation energy of 53 kJ mol⁻¹ to be determined for the rate-limiting step. This value agrees very well with a published value for the leaching of Ca from wollastonite in acidic conditions and suggests that Ca leaching is the rate-limiting step in wollastonite carbonation at these temperatures.