Perlite’s Contribution to Phosphoric acid and Phosphorous fertilizers production

Phosphate rocks play a crucial role in ensuring the availability of phosphorous for the world’s food needs. Phosphate rocks are used to manufacture phosphoric acid in the wet process as well as Phosphorous fertilizers. Phosphoric acid is manufactured from phosphate ores using thermal and wet processes. In industry, the wet process is more commonly used due to its lower energy requirements compared to the thermal process and, thus, greater economic viability.[1]

Wet process phosphoric acid (WPA) manufacturing is mainly via the dihydrate process. Phosphogypsum is the by-product. The size distribution of phosphogypsum is a major factor for the economics of the process as it greatly affects filtration efficiency of the acid. [2]

Although there is a great variety of rocks, different phosphoric acid processes and plant procedures, the problems associated with WPA production are basically similar. Since rather low grade and low-quality rocks are increasingly processed worldwide, there is an upward trend to add mineral modifiers such as clays and silicas (perlite included), to these rocks. These amend rock behavior and overcome problems in WPA production. They increase gypsum filterability and washing, reduce corrosion and fluorine emission and improve the quality of the concentrated acid product and derived fertilizers. [3]

The silica content of the rock is in two forms. The active silica (clay) is beneficial as it reacts with fluorides in the rock and produces fluosilicates which due to the low solubility, readily precipitates and finally reduces corrosion. The other silica (quartz) is inert and will not affect the process chemistry, but causes erosion in the various digestor section equipment. The phosphate bearing mineral contains about 3-4% by weight F. Hence the rock should have enough active silica to fix fluorides while the inert silica should be minimum. For this, it is recommended to have activesilica/fluoride ratio of 0.5 and the total silica should not exceed 3%. [4]

Our target as in.mat-Lab is to develop and apply an Active Silica determination method as a tool for various perlite qualities evaluation and comparison for usage in WPA process industries.

Literature
[1] “Quality of Phosphate Rocks from Various Deposits Used in Wet Phosphoric Acid and P-Fertilizer Production”, Urszula Ryszko, Piotr Rusek and Dorota Kołodynska
[2] “Effect of calcinated and activated perlite on improving efficiency of dihydrate process for phosphoric acid” Boumnijel, Hedi Ben Amor, Cheker Chtara
[3] M. Schorr, I.J. Lin: “Wet process phosphoric acid – Production problems and solutions”, Industrial Minerals, April 1997, p.p.61-71.
[4] “Operating experience with different rock phosphates in nitrophosphate complex” V.S. Joshi and P.A. Shah G.N.F.C. Ltd, India[/vc_column_text][/vc_column][/vc_row]