Beneficiation of Low Grade Kaolin by High Shear Agitation with Dispersant (HSD) Pre-Treatment for High Yield and Improved Fired Colour

Abstract

Crude kaolin contains various amounts of discolouring elements such as anatase (TiO2), mica and iron oxide (Fe2O3), which give low brightness and are detrimental in use. In addition, the anatase (titaniferrous) and mica can also contain iron contaminants. Beneficiation of two crude low grade china clays, marked as KY and SR, was attempted through imitating existing industrial practice of levigation and hydrocyclone classification, and through an innovative technique of high shear agitation with dispersant (HSD) pre-treatment. HSD treated clays were subjected to impurity removal by sieving, demagnetizing and coarse/heavy impurity removal by sedimentation under gravity techniques. The results in terms of yield of clay (% on feed basis), grade of clay (kaolinite%) and effect of purified clays on the whiteness of porcelain were compared. It was found that by use of HSD pre-treatment, SR dump clay could be purified to contain 90.7% kaolinite and 0.75% free silica with a striking yield of 62.32% as compared to 88.90% kaolinite, 3.34% free silica and 30.2% only as yield by levigation and hydrocyclone. The KY dump clay was purified to contain 85.51% kaolinite and only 5.57% free silica with 44.3% yield by HSD pre-treatment as compared to 72.29% kaolinite, 16.29% free silica and 30.4% only as the yield by levigation and hydrocyclone classification. The kaolinite enrichment and removal of free silica to a major extent and chromophore impurities (although to a minor extent) in these dump clays after beneficiation rendered them suitable for polished vitrified porcelain tiles application as far as the development of white fired colour in the tiles body is concerned.