Reduction of insoluble content of a Selenite sample from Rajasthan

Reduction of insoluble content of a Selenite was received from M/s. Bikaner Gypsums Ltd., Calcutta, assaying 45.16% SO3, 31.71% CaO, 1.06% Insolubles 0.29% CO and traces of NaCl, MgO etc. The impurity was clay present as inclusions of pockets and stringers within the crystal aggregates of Selenite which was liberated mostly at about 6-10 mm size. For complete liberation, grinding to -28 mesh was indicated. Batch tests showed that bulk of the clay could be eliminated after washing the ¾ “ size sample and desliming. For further removal of clay finer grinding to about -20 mesh followed by further washing is necessary. Based on the batch tests results, pilot plant scale tests were conducted following the same procedure. The ¾ “ washed sand assayed 0.59% insolubles, which on further grinding and desliming yielded a mixed sand product weighing 73.2% and assaying 0.4% insoluble corresponding to about 99.6% Selenite equivalent. The product was of acceptable grade.