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Elcad flourine emission11/5/2022 The tri calcium phosphate is converted by reaction with concentrated sulphuric acid into phosphoric acid and insoluble calcium sulphate. The vacuum must be released during the discharge of the cake and it is beneficial to blow air through in the reverse direction at this The cake must then be discharged and the cloth efficiently washed to clear it of any remaining solids which might otherwise build up and impair filtration in subsequent cycles. The remaining liquid must be removed from the filter cake as far as possible at the end of the washing sequence. It is only possible to achieve the desired degree of separation at a reasonable rate if the filtration is either pressure or vacuum assisted and in practice vacuum is always used. The initial separation must be followed by at least two stages of washing, to ensure a satisfactory recovery of soluble P2O5. The filter medium must move in sequence through the various stages for continuous operation. Five tonnes of gypsum are generated for every tonne (P2O5) of product acid produced. This stage separates the phosphoric acid from the calcium sulphate dihydrate. Some grades of commercial rock do not need grinding ,their particle size distribution being acceptable for dihydrate reaction section (60_70% <150) most other phosphate rock need particle size reductio Generally using ball or rod mills. Nowadays phosphoric acid is produced from phosphatic o mined in different parts of the world.Bones used to be principal natural source of phosphoric a.Let us see the manufacture of phosphoric acid by wet proc Involving sulfuric acid leaching of dihydrate process. Only one scrubbing stage is generally used and 17-23% fluosilicic acid is obtained with a recovery efficiency of about 83-86%. Essentially, this removes any P2O5 values from the gas. Gas from the evaporator flash chamber is first fed through an entrainment separator if a system operating under vacuum is used. Fresh water, recycled pond water, sea water and dilute fluosilicic acid have all been used as scrubbing liquor. Silica is removed from the acid by filtration. A product containing up to 22% fluosilicic acid is recovered in the fluoride recovery system at atmospheric pressure and the removal efficiency is better than 99% (90% with one absorber). The most widely used scrubber is the void spray tower operating at atmospheric pressure but others, such as packed bed, cross-flow venturi and cyclonic column scrubbers have been Extensively employed. These can vary both in the scrubbing liquor and in the type of scrubber used. H2SiF6 SiF4 +2HFĪ number of different scrubbing systems have been used for removing fluoride. The fluosilicic acid may decompose under the influence of heat to give volatile silicon tetrafluoride and hydrogen fluoride. In the presence of silica this reacts readily to form fluosilicic acid via silicon tetrafluoride. The fluorine is liberated as hydrogen fluoride during the acidulation of phosphate rock. The phosphate minerals in both types of ore are of the apatite group, of which the most commonly encountered variants are:– Fluorapatite Ca10(PO4)6(FOH)2 – Francolite Ca10(PO4)6–x(CO3)x(FOH)2+x Fluorapatite predominates in igneous phosphate rocks and francolite predominates in sedimentary phosphate rocks. – Sedimentary as found in Morocco, Algeria, Jordan U.S.A., etc. Phosphate ores are of two major geological origins:– Igneous as found in Kola, South Africa, Brazil, etc. Raw Materials for Phosphoric Acid Productionīones used to be the principal natural source of phosphorus but phosphoric acid today is produced from phosphatic ores mined in various parts of the world.
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