CO2 reacted in the period of fast reaction rate with respect to that of the reaction stoichiometry for complete conversion of CaO to CaCO3. As seen in Figure 2, while mass after calcination remains constant, the mass change upon carbonation- the carrying capacity- reduces with a large number of cycles. In calcination, porous CaO (molar volume = ) is formed in place of CaCO3 (.). On the other hand, in carbonation, the CaCO3 formed on the surface of a CaO particle occupies a larger molar volume. As a result, once a layer of carbonate has formed on the surface (including on the large internal surface of porous CaO), it impedes further CO2 capture. This product layer grows over the pores and seals them off, forcing carbonation to follow a slower, diffusion dependent mechanism. Sintering CaO is also prone to sintering, or change in pore shape, shrinkage and grain growth during heating. Ionic compounds such as CaO mostly sinter because of volume diffusion or lattice diffusion mechanics. As described by sintering theory, vacancies generated by temperature sensitive defects direct void sites from smaller to larger ones, explaining the observed growth of large pores and the shrinkage of small pores in cycled limestone. It was found that sintering of CaO increases at higher temperatures and longer calcination durations, whereas carbonation time has minimal effect on particle sintering. A sharp increase in sintering of particles is observed at temperatures above 1173 K, causing a reduction in reactive surface area and a corresponding decrease in reactivity. Solutions: Several options to reduce sorbent deactivation are currently being researched. An ideal sorbent would be mechanically strong, maintain its reactive surface through repeated cycles, and be reasonably inexpensive. Using thermally pre-activated particles or reactivating spent sorbents through hydration are two promising options. Thermally pre-activated particles have been found to retain activity for up to a thousand cycles. Similarly, particles reactivated by hydration show improved long term (after~20 cycles) conversions. Disposal of waste sorbent Properties of waste sorbent After cycling several times and being removed from the calcium loop, the waste sorbent will have attrited, sulfated and become mixed with the ash from any fuel used. The amount of ash in the waste sorbent will depend on the fraction of the sorbent being removed and the ash and calorific content of the fuel. The size fraction of the sorbent is dependent on the original size fraction but also