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.
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.
Adachi, Y., Kobayashi, A. and Kobayashi, M. (2012) Structure of coloidal flocs in relation to the dynamic of properties of unstable suspension, International Journal of Polymer Science, Vol. 2012, Article ID 574878, 10 p.
Barany, S., Meszaros, R., Kozakova, I. and Skvarla, I. (2009) Kinetics and mechanism of flocculation of bentonite and kaolin suspensions with polyelectrolytes and the strength of flocs, Colloid Journal, Vol. 71, No. 3, pp. 285–292.
Carissimi, E. and Rubio, J. (2005a) The flocs generator reactor-FGR: a new basis for flocculation and solid-liquid separation, International Journal of Mineral Processing, Vol. 75, pp. 237–247.
Carissimi, E. and Rubio, J. (2005b) Advances in particulates aggregation-flotation separation, in Proceedings of Centenary of Flotation Symposium 2005, G.J. Johnson (ed), 6–9 June 2005, Australia, electronic resource, 10 p.
Carissimi, E., Miller, J.D. and Rubio, J. (2007) Characterisation of the high kinetic energy dissipation of the flocs generator reactor, International Journal of Mineral Processing, Vol. 85, pp. 41–49.
Cioncolini, A. and Santini, L. (2006) An experimental investigation regarding the laminar to turbulent flow transition in helically coiled pipes, Experimental Thermal and Fluid Science, Vol. 30, pp. 367–380.
Du, J., Pushkarova, R.A. and Smart, R. St.C. (2009) A cryo_SEM study of aggregate and floc structure changes during clay settling and raking processes, International Journal of Mineral Processing, Vol. 93, pp. 66–72.
Elmaleh, S. and Jabbouri, A. (1991) Flocculation energy requirement, Water Research, Vol. 25, No. 8, pp. 939–943.
Fawell, P.D., Farrow, J.B., Heath, A.R., Nguyen, T.V., Owen, A.T., Paterson, D., Rudman, M., Scales, P.J., Simic, K., Stephens, D.W., Smith, J.D. and Usher, S.P. (2009) 20 years of AMIRA P266 “Improving Thickener Technology”: How has it changed the understanding of thickener performance, in Proceedings 12th International Seminar on Paste and Thickened Tailings (Paste09), R.J. Jewell, A.B. Fourie, S. Barrera, J. Wiertz (eds), 21–24 April 2009, Viña Del Mar, Chile, Gecamin Limited, Santiago, Australian Centre for Geomechanics, Perth, pp. 59–68.
Farrow, J.B., Johnston, R.R.M., Simic, K. and Swift, J.D. (2000) Consolidation and aggregate densification during gravity thickening, Chemical Engineering Journal, Vol. 80, pp. 141–148.
Germano, M. (1989) The Dean equations extended to a helical pipe flow, Journal of Fluid Mechanics, Vol. 203, pp. 289–305.
Hogg, R. (2000) Flocculation and dewatering, International Journal of Mineral Processing, Vol. 58, pp. 223–236.
Huttl, T.J. and Friedrich, R. (2000) Influence of curvature and torsion on turbulent flow in helically coiled pipes, International Journal of Heat and Fluid Flow, Vol. 21, pp. 345–353.
Manno, P., Moulin, P., Rouch, J.C., Clifton, M. and Aptel, P. (1998) Mass transfer improvement in helically wound hollow fibre ultrafiltration modules yeast suspension, Separation and Purification Technology, Vol. 14, pp. 175–182.
Owen, A.T., Fawell, P.D., Swift, J.D., Labbett, D.M., Benn, F.A. and Farrow, J.B. (2008) Using turbulent pipe flow to study the factors affecting polymer-bridging flocculation of mineral systems, International Journal of Mineral Processing, Vol. 87, pp. 90–99.
Sreenivasan, K.R. and Stykowski, A.J. (1983) Stabilisation effects in flow through helically coiled pipes, Experiments in Fluids, Vol. 1, Issue 1, pp. 31–36.
Tse, I.C., Swetland, K., Weber-Shirk, M.L. and Lion, L.W. (2011) Fluid shear influences on the performance of hydraulic flocculation systems, Water Research, Vol. 45 (17), pp. 5412–5418.
Webster, D.R. and Humphrey, J.A.C. (1993) Experimental observation of flow instability in a helical coil, Transactions of the ASME: Journal of Fluids Engineering, Vol. 115, pp. 436–443.
White, R.B., S̆utalo, I.D. and Nguyen, T. (2003) Fluid flow in thickener feedwell models, Minerals Engineering, Vol. 16, Issue 2, pp. 145–150.