Patent ID: 6287532
Filing Date: 2001-09-11
Classification: C01F,C01G,C01P,H01L

Abstract:
A process for producing a hydrotalcite compound derived from a water-soluble magnesium compound and a water-soluble aluminium compound which contain(s) at least 50 ng/g (ppb) of a uranium compound as calculated in terms of uranium (U) based on Mg(OH).sub.2 and/or Al(OH).sub.3, said hydrotalcite compounds being represented by the formula (1) below:Mg.sub.1-X.sup.2+ Al.sub.X.sup.3+ (OH).sub.2 A.sub.X/2.sup.2-.multidot.mH.sub.2 O (1)in whichx is a positive number in the range of 0.2.ltoreq.x.ltoreq.0.5,A.sup.2- is at least one of CO.sub.3.sup.2- and SO.sub.4.sup.2-, andm is a number in the range of 0-2, having an average secondary particle size of not more than 3 .mu.m and a BET specific surface area of not more than 30 m.sup.2 /g and wherein they have a uranium (U) content of not more than 10 ppb,which comprises(1) subjecting an aqueous solution of the water-soluble aluminium compound and the water-soluble magnesium compound, which as a whole contain a uranium compound in an amount corresponding to at least 50 ng of uranium (U) as calculated per gram of Mg(OH).sub.2 and/or Al(OH).sub.3, to a coprecipitation reaction under alkaline conditions, the composition of the starting materials satisfying the molar ratio within the range defined by the formula (2) below: ##EQU3##at temperatures of 10-50.degree. C. under stirring, and(2) subjecting the resulting coprecipitation product, without isolating it from the suspension which served as the mother liquor of the coprecipitation reaction, to a hydrothermal reaction at a temperature of 90-200.degree. C. for at least 0.5 hour, while keeping the pH of the reaction suspension within the range of 7.0-13.5.