Correlation between particle size and surface area for chlorite and K-feldspar

The specific surface area as determined by BET analysis is often used for scaling mineral surface reaction capacities and rates between particles of different sizes as found in nature. Generally, an inverse proportionality between BET area and particle size is assumed, based on geometry. However, macroscopic laboratory studies of mineral surface reactions generally employ crushed material that may have been mechanically disturbed, potentially leading to an artificial increase in the specific surface area, and a change in the apparent surface reactivity. In this study, we determine the BET area for natural K-feldspar and chlorite samples from Sweden as function of particle size in a first step towards relating the surface reactivity for these minerals to grain size. Byegård et al. (1998) and André et al. (2009) for granite and Dubois et al. (2010) for natural magnetite and labradorite, have observed a deviation from linearity when relatively large particle size fractions are considered. André et al. (2009) proposed that this was due to artificial, new surfaces associated with newly developed microcracks within a mechanically disturbed zone at the particle edge. This work aims at studying the dependency of the specific surface area, measured via the BET method, and the particle size for two common silicate minerals, chlorite and K-feldspar.