Physical Separation '22 Day 3: Classification, and panel discussion on the future of physical separation

Wednesday 11th May

The theme of the final day's technical session was Classification and Solid-Liquid Separation, with eight presentations, from Australia, Canada, Chile, India and Peru.

Perhaps the most ubiquitous separation machine in the minerals industry is the hydrocyclone, and five of the presentations involved the use and design of these important devices.

Shashank Shekhar Pathak, of Weir EnSci, Weir Mineral India, presented a theoretical approach to develop a predictive model of the air core in hydrocyclones and Shuvam Mohanty, of the University of New South Wales, Australia, described the parametric analysis of axial flow hydrocyclones with suitably designed numerical experiments at various operating conditions. The effect of inlet dimensions, vortex finder length, and vortex finder diameter on the performance and flow pattern were computationally investigated using large eddy simulation for twelve hydrocyclone separators altogether. The results shows that the maximum tangential velocity and axial velocity profiles in the hydrocyclone decreases with increasing inlet dimensions, vortex finder length and diameter. 

The handling of tailings is of great importance in mining. Efficient tailing management is necessary for safe disposal as well as reutilisation of tailings to provide a sustainable solution to the modern mining industry. The Double Effect (DE) hydrocyclone is a double efficiency classification unit, working as a single stage without the need for additional pumping. The double classification helps dramatically reduce the amount of fine material entrained by coarse material, that might occur with a single stage and, at the same time, helps improve water recovery in the process. Chandranath Banerjee, of Weir EnSci, Weir Mineral India, presented a parametric study to analyse the physical response of design and operating variables of a DE hydrocyclone on the classification behaviour of mine tailings.

The KREBS CycloWash is an FLSmidth patented, ancillary elutriation (cleaning) device that markedly improves the desliming performance of standard cyclones, as it also reduces operating costs. The CycloWash, located in the lower/apex section of the hydrocyclone, injects water into the cyclone, and the injection water displaces the fines-laden water in the partially thickened underflow pulp. The result, essentially, is a second stage of classification taking place, where the displaced water with fines joins the normal cyclone overflow. The coarse solids are thickened, and they discharge through the apex orifice as a thoroughly deslimed underflow. 

Pablo Hinojosa, of UNSA, Peru, said that there must be a contingency plan for the classification of tailings via hydrocyclones in situations of high fines in the tailings entrance feed, so that actions including shutting down cyclones are avoided. If cyclones are closed, the pressure will increase and therefore more sand will be lost in the overflow (especially in conditions of tailings with good quality of input material, that is, a feed with coarse quality). He proposed reducing the content of fines in the underflow by reducing the diameter of the truncated cone of the CycloWash (a size that is close to the diameter of the apex), with the aim of improving the quality of underflow. In this way, a better quality underflow will be obtained when there is a high content of fines in the feed.

The design and operation of hydrocyclone cluster distributors is reported to have a significant impact on grinding circuit classification and therefore the overall minerals processing circuit performance.  Nirmal Weerasekara, of Weir Minerals, Australia, introduced a novel approach of assessing the performance of hydrocyclone distributors by employing a coupling between Computational Fluid Dynamics assessment and JKSimMet cyclone assessment, including classification and roping detection, novel hydrocyclone distributor designs then being compared against traditional designs using this approach.

According to Joshua Starrett, of the University of Newcastle, Australia, high-performance particle size classification is emerging as an enabler for achieving step change improvement in mineral beneficiation. He said that conventional mechanical screens provide sharp separations but are limited by decreasing performance at lower cut sizes and impacts of wear. Similarly, traditional devices such as hydrocyclones can offer good separations but are significantly impacted by water entrainment of fine particles. Joshua presented a study utilising a REFLUX™ Classifier, with water as a fluidising medium, to classify feed suspensions based on particle size. The partition curves were remarkably sharp, exhibiting virtually no ultrafine entrainment with the coarse underflow, and virtually no oversize particles in the overflow. 

The slurry flow properties in the compression zone of a thickener are challenging to predict, mainly due to the high concentration of solids causing non-Newtonian flow behavior. More accurate prediction of slurry sliding velocity at the thickener floor would enable the development of better thickener models, control strategies, and unit designs. An inclined open flume is often used to investigate such flows, where the slurry with known properties is fed and monitored as gravity-driven. Guilherme Anrain, of University of British Columbia, Canada, presented work using open-channel flow data available from the literature and data from their experiments to train machine-learning models — parameters including flow rate, flume slope, slurry depth, and slurry rheological properties.

In the final presentation in the session Christian Ihle, of the University of Chile, highlighted how water shortage and low ore grades present in many mineral processing plants lead to high water recirculation, which can lead to low water quality without proper treatment. Inclined plate clarifiers are a low footprint solution to remove turbidity from such streams. The presentation focused on the study of the effect of heating of the downward facing wall of such inclined elements, both on particles settling and re-suspension. 

After a short break, Erin Bobicki, of the University of Alberta, Canada, chaired a two hour panel discussion on 'Looking to the Future: Physical Separation in 2030'. The panelists were Peter Amelunxen, formerly with Hudbay Minerals, Canada, now Vice-President of Technical Services at Capstone Copper, Canada, Priscila Esteves, of Steinert, Brazil, Kevin Galvin, of University of Newcastle, Australia, and Neil Rowson of the University of Birmingham, UK.

There was wide range of discussion, including how different processes, such as gravity, flotation and magnetic separation will need to be integrated more in future as ores become more complex. It was a superb discussion, led by an excellent chairperson in Erin Bobicki, with highly experienced panelists with diverse specialties. It should be essential viewing for anyone in our industry.

Following the discussion, Jon Wills thanked the panelists and all those who have presented work over the last 3 days. He hoped that by the time of the next Physical Separation conference, in two years time, we would be meeting face to face again in Falmouth.

The recordings of the panel discussion and all the presentations at the conference are available on demand for the next 6 months, so it is not too late to register to access these.

All presenters have been invited to submit papers on their work for peer-review in a virtual special issue of Minerals Engineering.

Once again, we thank our sponsors for their support throughout these difficult times.

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