Importance

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Abstract

The present invention is directed to the preparation of gypsum plaster prepared from gypsum rock having a substantial salt content to render it more suitable for manufacturing processes such as the manufacture of gypsum board by rapid and intimate mixing with a flow of water followed by rapid separation of the bulk of the water, the recovered purified wet or damp plaster being used at once in the manufacturing process before an unacceptable degree of hydration has occurred. It is preferred to use for the washing cold water, say up to 40.degree. C. and to add no retarder or other additive at the washing stage in order to minimize cost and avoid interference with the subsequent manufacturing process. The time elapsing between contacting the plaster with water and recovery of wet purified plaster preferably does not exceed 30 seconds. A rotary or vortical mixer may be used and the preferred means for rapid separation is a continuous decanting centrifuge having a cone angle not exceeding 7.degree..

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First Claim