Authors: Nugraha, T; Fourie, AB; Leong, YK; Avadiar, L

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Nugraha, T, Fourie, AB, Leong, YK & Avadiar, L 2013, 'The utilisation of a coiled plug flow reactor for the flocculation of kaolin slurry', in R Jewell, AB Fourie, J Caldwell & J Pimenta (eds), Proceedings of the 16th International Seminar on Paste and Thickened Tailings, Australian Centre for Geomechanics, Perth, pp. 175-184.

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Abstract:
The flocculation of mine tailing slurries to facilitate the consolidation of the slurries and separation of water was studied by using kaolin slurry as a model material. The mixing and reactions between kaolin slurry with flocculants (Magnafloc 336) occurred in a coiled Plug Flow Reactor (cPFR) which was constructed from 2.54 cm inner diameter plastic tubing, 10 m long, and coiled at a diameter of 20 cm. The flocculant was added into the slurry stream through two or four flocculant injection points along the cPFR. The kaolin slurries used during the experiment were set at 3 wt% and 8 wt%, while the flocculant application was varied between 26–75 g/ton (dry weight solid based). The performance of the cPFR was characterised by calculating various parameters that included the Reynolds number, as well as Dean number and Germano number to accommodate the effects of the curvature and torsion of the cPFR. Shear could also be evaluated based on the measured pressure drop across the reactor. The flocculated slurry that was produced in the cPFR was then sent to a settling column (17.6 cm diameter, 140 cm high) where settling rates were measured. The settling column was also equipped with a gamma-radiation-based density gauge. The results showed that despite the short residence time (14.8 s) within the cPFR, the reaction could occur to a sufficient extent to produce settling rates of 10.3–25.7 m/hour, at initial kaolin concentration of 3 wt% with flocculant concentrations between 26–75 g/ton. At an initial kaolin concentration of 8 wt%, the settling rate was found to be between 0.6–25.1 m/hr. Furthermore, it was also observed that settling rates did not only increase with concentration of flocculant, but also increased when the flocculant injection points were changed from two points to four points along the cPFR. The impact of the changes in the flocculant injection points was more significant at higher solids concentration. The higher settling rate was correlated with optical microscopy data, which clearly showed larger size of particles of the flocculated slurry at higher settling rates. The density gauge also showed that slurry density was not uniform with height. The bottom of the sedimented slurry consistently showed higher density than the layer above it. Moreover, the distribution of the slurry density with height continued to change during settling, while some sudden increase in density could be observed following raking.

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