Abstract
During phosphoric acid manufacture, phosphate rock is reacted with sulfuric acid and the by-product, gypsum, is separated using vacuum, belt or pan filters. Filtration efficiency is known to depend on the size distribution and shape of the gypsum crystals. These properties are influenced by several process variables such as solids loading, phosphoric and sulfuric acid concentration, impurities present in the rock and temperature. Successful control of these parameters to yield optimum filtration efficiency in industrial scale has often been difficult. Alternately, the use of chemical additives to attain a consistent filter cake has been examined in the past. In this study, the addition of poly-1-glutamic acid and polyvinyl sulfonate on the crystal habit modification of dihydrate and hemihydrate were investigated. Enhanced filtration rates were obtained with both the additives and the filtration efficiency exhibited a direct correlation with the aspect ratio of the crystals formed. High sulfate concentration was also found to result in increased filtration rates.
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