Imerys Phosphate Production Additive is vital in the production of phosphoric acid when the phosphate rocks being used have a weight ratio of “active SiO2”/F lower than 0.53 or if, in general, its “active SiO2” content is considered low. “Active SiO2” is essential in order for the released HF to be captured during Phosphate Production.
Moreover, when ”low active SiO2 content of phosphate rock” is the case, the resulting by-produced gypsum dihydrate is characterized by needle-type crystallization, which inhibits the subsequent acid/gypsum filtration process, dramatically reducing the phosphoric plant’s capacity and economic viability. Phosphate Production Additive addition changes completely the morphology of the gypsum dihydrate crystals, thus improving significantly the filtration rate.
To solve these two problems (HF and Gypsum needles), Imerys active perlite is co-fed with phosphate rock at a calculated rate to correct the active SiO2/F ratio to at least 0.53 (and adjust the Al2O3/P2O5 rate, which is also important, to approx 0.020), The gypsum crystal habitus then changes from to a cluster-like shape whose specific surface area is significantly smaller. Filtration rates soar as a result, to sometimes double or even triple “pre-perlite” values but at the same P2O5 recovery yield (around 95%). In addition to the increased efficiency in filtration, the addition of perlite also results in a reduction in overall plant corrosion caused by HF, and a reduction of HF emissions to the atmosphere.