REVERSIBLE TRANSFORMATION BETWEEN ARAGONITE AND CALCITE INDUCED BY MECHANICAL MILLING AT LOW TEMPERATURE

The mechanical milling of biogenic aragonite and calcite was performed at room temperature with milling time of 1min~10hand the milled products were characterized with XRD and SEM.The results show that the reversible transformation between aragonite and calcite can be realized by milling at low temperature.In fact,the pure aragonite begins to transform into calcite after 15min milling.On further milling for about 1h,the calcite proportion amounts to the maximum of about 33%,however,gradually decreases to an equilibrium value with more than 1h milling.In comparison,the pure calcite begins to transform into aragonite only after 5hmilling.On further milling,the aragonite proportion increases rapidly to about 80%,then gradually increases to an equilibrium value after more than 6.5hmilling.The milled products always reach a similar equilibrium value(aragonite-88%,calcite-12%)after enough milling time,independent of the original material composition.Therefore,the milling-induced transformation between aragonite and calcite is consistent with Le Chatelier′s principle.