Zeolite prodn. with low fluoride content - in calcium fluoride mfr. from hexa:fluorosilicic acid by adding aluminium sulphate during pptn. to give stable silica sol.

摘要

Prodn. of zeolites lowin fluoride from SiO2 sol and alkali aluminate involves reacting H2SiF6 in aq. solb. with CaCO3 at 20-100 degrees C in the presence of a mole Al2(SO4)3/mole H2SiF6 (a = 0.01-0.33, pref. 0.05-0.1) so that a pH of 1.0-5.5 is attained. The CaF2 pptw. formed is filtered off, then the filtrate, which is a SiO2 sol, is mixed with an alkaline soln. of b mole alkali (na)aliminate ( is not 2a) and kept at 70-100 degrees C. The crystalline (Na) zeolite (esp. zeolite A) formed is sepd. Process makes possible the conversion of SiO2 obtd. in the mfr. of CaF2 from H2SiF6 into zeolite, since a stable fluid SiO2 sol is obtd., rather than a gel which is difficult to process. The process is suitable for batch or continuous operation.