Authors: Sofrà, F; Bhattacharjee, P

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Sofrà, F & Bhattacharjee, P 2021, 'Online yield stress measurement for real-time process control', in AB Fourie & D Reid (eds), Paste 2021: 24th International Conference on Paste, Thickened and Filtered Tailings, Australian Centre for Geomechanics, Perth, pp. 119-130,

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The authors report a robust estimate of the shear yield stress of a slurry from inline measurement of a flowing slurry process stream. At present, slurry density is often used as a proxy in estimating the shear yield stress based on laboratory-scale measurements performed as a function of solids concentration. However, this approach leads to inaccuracies due to poor translation of laboratory data to operational situations and fluctuations in the sensitive yield stress-concentration dependence due to material and process variations. A robust inline measurement that directly relates to the in situ yield stress is therefore both a valuable and significant advance. In order to provide continual, inline rheology data for process control, the OnLine Rheometer Series 1000 (OLR) was piloted for a high clay, gold process thickener underflow in a pilot pipe loop facility. Benchtop measurements of the vane yield stress, and solids concentration were performed on samples drawn from the line as the circulating liquid was progressively diluted. The measured vane yield stress was compared with the Yield Stress Index (YSI), a native function available in the software of the OLR, over a concentration (c) ranging between 49.4 wt% < c < 64.5 wt%. Over the concentration range studied, the vane yield stress exponentially increased with concentration and ranged between 4 and 65 Pa while the YSI values ranged between 16 and 131 units showing an identical dependence on concentration. Importantly, it was found that the YSI correlated linearly with the yield stress values measured using the vane. It follows that the YSI metric can be used to estimate the yield stress within a small factor in actual operations. This finding supports the use of the YSI as an inline control variable in mineral processing and tailings management operations; in thickening and paste preparation for example.

Keywords: rheology, yield stress, online measurement, automation

Bell, D, Binding, D & Walters, K 2006, ‘The oscillatory squeeze flow rheometer: comprehensive theory and a new experimental facility’, Rheologica Acta, vol. 46, no. 1, pp. 111–121.
Colombo, G, Kim, S, Schweizer, T, Schroyen, B, Clasen, C, Mewis, J & Vermant, J 2017, ‘Superposition rheology and anisotropy in rheological properties of sheared colloidal gels’, Journal of Rheology, vol. 61, pp. 5, pp. 1035–1048.
Field, JS, Swain, MV & Phan-Thien, N 1996, ‘An experimental investigation of the use of random squeezing to determine the complex modulus of viscoelastic fluids’, Journal of Non-Newtonian Fluid Mechanics, vol. 65, pp. 177–194.
Hoekstra, H, Mewis, J Narayanan, T & Vermant, J 2005, ‘Multi length scale analysis of the microstructure in sticky sphere dispersions during shear flow’, Langmuir, vol. 21, pp. 11017–11025.
Hoekstra, H, Vermant, J, Mewis, J & Fuller, GG 2003,’Flow-induced anisotropy and reversible aggregation in two-dimensional suspensions’, Langmuir, vol. 19, pp. 9134–9141.
Kim, M, Eberle, APR, Gurnon, AK, Porcar, L & Wagner, NJ 2014, ‘The microstructure and rheology of a model, thixotropic nanoparticle gel under steady shear and large amplitude oscillatory shear (LAOS)’, Journal of Rheology, vol. 58, pp. 1301–1328.
Konigsberg, D, Nicholson, T, Halley, P, Kealy, T & Bhattacharjee, P 2013, ‘Online process rheometry using oscillatory squeeze flow’, Applied Rheology, vol. 23, no. 3,
Nguyen, QD & Boger, DV 1983, ‘Yield stress measurement for concentrated suspensions’, Journal of Rheology, vol. 27, no. 4,
pp. 321–349.
Nguyen, QD & Boger, DV 1985, ‘Direct yield stress measurement with the vane method’. Journal of Rheology, vol. 29, no. 3,
pp. 335–347.
Nguyen, QD & Boger, DV 1992,’ Measuring the flow properties of yield stress fluids’, Annual Review of Fluid Mechanics, vol. 24, no. 1, pp. 47–88.
Schroyen, B, Swan, JW, Van Puyvelde, P & Vermant, J 2017, ‘Quantifying the dispersion quality of partially aggregated colloidal dispersions by high frequency rheology’, Soft Matter, vol. 13, no. 43, pp. 7897–7906.
Sofrà, F & Boger, DV 2002, ‘Environmental rheology for waste minimisation in the minerals industry’, The Chemical Engineering Journal, vol. 86, pp. 319–330.
Sofrà, F, Boger, DV & Scales, PJ 2015, ‘Rheological concepts’, in RJ Jewel & AB Fourie (eds), Paste and Thickened Tailings – A Guide, 3rd edn., Australian Centre for Geomechanics, Perth.
Varadan, P & Solomon, MJ 2001, ‘Shear-induced microstructural evolution of thermoreversible colloidal gel’, Langmuir, vol. 17, pp. 2918–2929.
Vermant, J, Walker, L, Moldenaers, P & Mewis, J 1998, ‘Orthogonal versus parallel superposition measurements’, Journal of NonNewtonian Fluid Mechanics, vol. 79, pp. 173–189.

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