CRUDE KAOLIN DISSOLUTION IN THE ABSENCE AND PRESENCE OF SODIUM POLY(ACRYLIC ACID), SODIUM HEXAMETAPHOSPHATE, AND SODIUM SILICATE UNDER DIFFERENT EXPERIMENTAL CONDITIONS

Abstract

The influence of anionic dispersing agents, such as sodium poly(acrylic acid), sodium hexametaphosphate, and sodium silicate on the dissolution of crude kaolin was examined by measuring the dissolved metals produced in the absence and presence of dispersing agents. For this purpose, the rheological and structural changes caused by the dissolution of kaolin metal constituents were studied in batch mode using several parameters, namely, solids (wt.%), pH, contact time (aging), and dispersing agent dose. A noteworthy increase in kaolin dissolution was caused by the presence of dispersing agents, particularly poly(acrylic acid) and sodium hexametaphosphate. These agents produced conspicuously large amounts of dissolved Al in comparison to the other experimental treatments. Little dissolved Si was measured under similar conditions in distilled water, but the amount of Si released using dispersing agents was nearly double that observed in distilled water only. Excess dispersing agents interacted with kaolin and dissolved accessory elements in the kaolin (i.e. Fe, Ca, Mg) and thus released enough Fe to form a stable Fe-dispersant complex. The present study showed that this phenomenon also contributed to a significant increase in the release of dissolved Al and Si through complexation.