Process for producing a carbonate composition

Abstract

A process for obtaining a sodium hydroxide solution and a slurry of fine calcium carbonate particles suitable for use as a paper coating or filler pigment includes the initial step of reacting a calcium hydroxide with sodium carbonate under conditions effective to produce an aqueous slurry containing sodium hydroxide and calcium carbonate as a precipitate. The aqueous sodium hydroxide solution is then removed from the first slurry by suitable means such as filtration. The slurry is reconstituted, and a fine fraction comprising an aqueous slurry of fine metal carbonate particles is removed from by suitable means such as a classifying device. The second half of the process can be used independently to process mined calcium carbonate. This includes steps of classifying the carbonate slurry to remove a coarse fraction comprising carbonate particles larger than a predetermined particle size to obtain a slurry of fine carbonate particles, grinding the coarse fraction to reduce the size of carbonate particles therein to form a ground product, and reclassifying the coarse fraction to obtain an additional quantity of a slurry of fine carbonate particles. The ground product is preferably combined with fresh aqueous slurry to form a combined product, and the classifying step is repeated continuously or intermittently in a closed circuit using the combined product to obtain a slurry of fine carbonate particles.