Reactivity and overburning tendency of quicklime burnt at high temperature

摘要

This study allowed the investigation of the burn-ability, overburning tendency, and lime slaking reactivity of carbonate rocks in the typical range of temperatures occurring in a TSR kiln firing solid fuels (1150 to 1300 ℃). Crushed rock fractions were submitted to burning and slaking tests. A multidisciplinary analytical approach, including chemical-physical, mineralogical-petrographic, crystallographic and thermal analyses, was carried out on raw materials and burnt products. The first part of the study allowed identification of the rock fabric and the impurity content, i.e. the mineralogical-petrographic composition, as key factors controlling the slaking rates and the overturning tendency of the lime at high temperature. Especially, coarse-sized granoblas-tic marbles, grain-supported and coralline limestones, presenting calcite cement fillings and/or replacements, are affected by higher overturning tendency than fine-grained marbles and/or mud-supported or micritic limestones. Moreover, hydraulic limes showed higher reactivity than pure limes at high temperature. This fact has to be related to the formation of different cementi-tious minerals at T > 1250 ℃, which slake at higher rates than the dead-burnt lime. Moreover, they could act as sintering inhibitors for the lime at high temperature [10]. Results from calcination kinetics analysis performed on massive samples allowed the conclusion that the higher the grain/crystal sizes of carbonate rocks are, the higher are the (apparent) activation energy, the calcination velocity, the starting calcination time/temperature and the slaking reactivity. This is consistent with a previous study performed on massive granulated samples reported by [18], and pseudomorphic and topotactic calcination reactions reported by [13].