| 摘要 |
PROBLEM TO BE SOLVED: To inexpensively recover silicon fluorice (SiF4 ) discharged from a phosphoric acid producing process by adding silicon dioxide when a rock phosphate is brought into contact with sulfuric acid soln. to produce phosphoric acid. SOLUTION: Silicon dioxide is added when rock phosphate is brought into contact with a sulfuric acid soln. to produce phosphoric acid, the resultant crude phosphoric acid is concd. and silicon fluoride (SiF4 ) is obtd. by decomposing hydrosilicofluoric acid (H2 SiF6 ) in generated vapor or a condensate with concd. sulfuric acid. The reaction of the rock phosphate with the sulfuric acid soln. is represented by the formula Ca10 (PO4 )6 F2 +10H2 SO4 +20H2 O→10CaSO4 .2H2 O+6H3 PO4 +2HF. This HF is converted into hyrosilicofluoric acid as shown by the formula 6HF+SiO2→H2 SiF6 +2H2 O by adding silicon dioxide at the time of the reaction. The SiF4 is then obtd. by decomposition represented by the formula H2 SiF6 (ap.)→SiF4 +2HF.
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