A study of thermal decomposition of antigorite from dunite and lizardite from peridotite

Two varieties of serpentines, antigorite and lizardite originated from dunite and peridotite, respectively, were previously undergone heat treatment in the range from 396 to 1128 °C and then leached via an original approach to the acid processing of dehydrated serpentines. Because of unsaturated (weak) Si–O(Si) bonds existing in the serpentines structure, ortho- [SiO 4 ] 4− , di- [Si 2 O 7 ] 6− and other silicate units are easily leached from dehydrated serpentines in the form of soluble silicic acids along with magnesium compounds via this approach, whereas the more complex fragments largely comprised of metasilicate [(SiO 3 ) 2− ] n chains remain in the unreacted mass The yields of silicic acids produced from heated serpentines are variable. The influence of thermal treatment on both the serpentinite samples was investigated by thermal, X-ray diffraction and chemical analyses. The data derived from the experimental studies allowed to reveal the distribution of primary ortho- [SiO 4 ] 4− and meta- [(SiO 3 ) 2− ] n silicate units in the silicate layers inherent in these serpentine minerals and to understand its influence on the mechanism of their decomposition including the high-temperature phase transformations into forsterite Mg 2 SiO 4 and enstatite Mg 2 Si 2 O 6 .