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Abstract

A process for the preparation of precipitated silica is disclosed. The precipitated silica has a refractive index from about 1.440 to about 1.450, among other properties. The silica is prepared by a method including; a first step of using an initial feedstock of water, an electrolytic salt and a fraction of the total amount of silicate employed; a second step including preneutralizing the feedstock with the acidifying agent until about 50 to 85% of the amount of M.sub.2 O present has been neutralized; a third step including introducing into the preneutralized feedstock the remaining fraction of alkali metal silicate in aqueous solution and the acidifying agent, under conditions such that the pH of the reaction medium remains substantially constant and from about 8.6 to about 9.6; a fourth step including, after the addition of silicate is stopped, in continuing the addition of acidifying agent until the medium reaches a pH of about 7 to 8; a fifth step including, after maturation, in continuing the acidification of the reaction medium until a silica broth with a pH of about 3.7 to 4.6 is obtained; wherein the consolidation ratio CR ##EQU1## of the process is less than or equal to 7, and the separated and dried silica is ground, if necessary, until an average particle diameter d.sub.50 from about 6 to about 13 .mu.m is obtained.

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First Claim