Tapping characterisation of high shear mixer agglomerates made with ultra-high viscosity binders

Abstract

The time-dependent consistency regimes produced during high shear mixing of zeolite powder and an ultra-high viscosity binder (linear alkylbenzene sulphonate (LAS) paste) were quantitatively described by the bulk aerated and tapped densities, which were determined using both hand and automated tapping techniques. The Hausner ratio was calculated, providing information on the inter-granular friction and cohesivity of the granular bulk as a function of mixing time. An agglomeration mechanism is proposed based upon the trend in Hausner ratio, which was confirmed by optical micrographs and granule size distribution data. The suggested mechanism comprises layering of zeolite particles onto an LAS paste core, breakage of powder-coated paste granules, micro-mixing of the granules, granule growth via coalescence, and finally granule consolidation.The bulk tapping data were analysed using the Kawakita equation and a logarithmic compaction approach. Three distinct compaction regions were identified with the latter analysis, the first of which was related to weak agglomerate break up, and the second and third to granule movement involving elastic and plastic granule deformations respectively during rearrangement. A variety of bulk compaction parameters were obtained, and their variation with mixing time is discussed. At least 10 times as many automated taps were required to reach the final tapped density in comparison to the hand-tapping procedure, and the final density was always lower than that obtained via hand-tapping. When the automated tapping data were scaled in terms of total number of taps and analysed, the parameters describing the bulk compressibility showed similar trends to those obtained from the hand-tapping procedure.