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

In line with the detailed investigations carried out in the laboratory for the separation and removal of colouring titanoferrous impurities from cryo-filtered Mamuara clay (Gujarat, India) based on high shear pretreatment and flotation, almost identical studies were carried out on cryo-filtered and bleached clay supplied by Amberger Kaolin Werke Eduard Kick GmbH & Co., Hirschau, Germany (AKW). Contrasting differences between Mamuara and AKW feed clays are in particle size, aspect ratio and viscosity. The same procedure, as described in Part I of this paper (Vol.38, Issue 1–2, Dec.2007) was followed for this investigation also. However, HSD and HSC were carried out at 50% solids only. The flotation feed, in noodle form, was reportedly prepared by subjecting the raw clay to blunging, de-gritting followed by hydrocycloning, flotation, cryofiltration (superconducting high gradient magnetic separation) and finally reductive bleaching and drying in the factory. Particle size distribution analysis showed 67% particles below 2 μm and about 43% below 1 μm. This material assayed as low as 0.3% of TiO ₂ and 0.49% Fe ₂O ₃ and measured a brightness of 83.4% ISO. AKW clay also showed a similar behaviour of interdependability for high shear pretreatment during initial test work as manifested by Mamuara clay. Hence detailed investigations were conducted to establish the nature of interdependence of HSD and HSC (time) with respect to titania removal. It could be shown that impurity removal increases as total pretreatment time increases up to a certain limit and the time required for HSD is at least twice of HSC time. This is totally opposite to that observed for Mamuara clay. Again, Aeropromoter 6494 was found better than 6493 and no frother is required when this collector is used. All other manifestations were very similar to that of Mamuara clay. While macro-flocculation of the impurity particles (devoid of air bubbles) occurred with 6493 at higher dosages, the same was not observed with 6494 with similar dosages. Using an IKA, KG stirrer (having 8 number of teeth on its rotor and develops a shear frequency of 2667 s ^{− 1}), the product titania could be reduced to 0.13% from a feed value of 0.3%. The flotation product measured 84.5% ISO brightness at a clay recovery of 92%. The titania removal is as high as 62.5%. The brightness was further improved to 85.2% by reductive bleaching.