Additional investigations on the separation of titanoferrous impurities from kaolin by high shear pretreatment and froth flotation — Part I

Abstract

Additional investigations were carried out in the laboratory for the separation and removal of colouring titanoferrous impurities from cryofiltered kaolin so as to elucidate more information on the effect of high shear pretreatment. The procedure consists of high shear agitation of a high solids clay slurry with the dispersant (high shear dispersion – HSD) followed by high shear agitation with the collector (high shear conditioning – HSC) as pretreatment steps and subsequently, reducing the pulp density and carrying out reverse flotation to float out the titanoferrous minerals. The flotation feed was prepared from a clay sample collected from Mamuara area of Gujarat, India. The raw clay was processed by centrifugation and cryofiltration. The cryofiltered clay forms the feed to flotation and consisted of 88–90% particles below 2 μm and about 70% below 1 μm. This material assayed 1.06% of TiO 2 and 0.29% Fe 2O 3 and measured a brightness of 83.4% and a yellowness of 7.1% ISO. Earlier studies gave the indication of interdependence of HSD and HSC (time) which was experimentally confirmed in the present investigation. It could be shown that impurity removal increases as total pretreatment time increases up to a certain limit and the time required for HSC is at least twice of HSD time. Higher shear intensities favour both the impurity liberation and collection. Most importantly, the shear frequency is found more influential than the shear rate for the overall flotation performance. At high shear frequencies, i.e., when a stirrer with more number of teeth on the rotor is used, the HSD/HSC time ratio shifts towards higher values so as to reduce the total time for pretreatment with improved titania removal. Re-optimisation of collector dosage based on these improved pretreatment conditions helped to remove more titanoferrous impurities. Lowest product titania achieved is 0.35% from a feed value of 1.06%. The flotation product measured 85% ISO brightness at a clay recovery of 86.4%. The brightness was further improved to 85.7% by reductive bleaching.