Increasing the Filtration Rate of Phosphor-gypsum by Using Mineral Additives

Phosphogypsum is a by-product of processing phosphate rock for phosphoric acid production by acidulation with sulfuric acid. The size of phosphogypsum crystals is a major factor for the economics of the process as it greatly affects the filterability of the phosphoric slurry. Some minerals containing two major chemical components, silica and alumina, proved to be very effective additives for growth of phosphogypsum crystals. To analyze the effect of these components on crystal growth, many additives are tested in the industrial scale in present work. Tests were carried out in the industrial phosphoric acid production unit of PP2 in Safi site.The present paper summarizes the results of phosphoric acid production from Youssoufia Washed Floated phosphate with addition of minerals aiming at increasing the filtration rate and better understand the effects of silica and alumina on filtration rates and phosphogypsum crystal size distribution.It is shown that the addition of reactive silica for complexation of the F element, which is unfavorable to a good crystallization, is seen to be insufficient in the absence of alumina; the crystals are developed, but in a single direction and become like thin bars. Furthermore, the presence of alumina improves the crystal morphology advantage with regular development along the three axes and achievement of large and uniform crystal shape.