The influence of exchangeable cation on thermal behaviour of ground vermiculite

Grinding and contact with water or salt solution increased the specific surface (ssa) but lowered the first dehydration effect (escaping up to 150degreesC) and increased the second dehydration effect (150 to 500degreesC). The dehydroxylation was moved to lower temperatures and was only DeltaM(500-1100degreesC)=3.7 +/- 0.3 % as compared to 5.5% in the parent vermiculite (V). Except DeltaM(20-150degreesC), the mass losses measured at the remaining T ranges, were consistent in the ground samples, thus the grinding for 2 min caused the homogenization of the crystal structure of vermiculite [DeltaM(150-500degreesC)=7.6 +/- 0.7%]. DTA curves after grinding and cation exchange indicate an important exothermal peak at 795-870degreesC, its temperature depending on exchangeable cation. It indicates the formation of high temperature phases (enstatite, forsterite, spinel). The lowest temperature of the peak (795degreesC) was observed in V-gr-Li, here lithium silicate was formed. The highest peak temperature (870degreesC) was found in V-gr-K, where almost only forsterite developed. These exothermal peaks were very weak in unground V with various exchangeable cations.