Physical Separation '22 Day 1: Gravity Concentration, and Plant Practice

Monday 9th May

Physical Separation '22 is the 7th in the MEI series, and the first to be totally online. We have a fine programme over the next three days, covering gravity and magnetic separation, sorting and microwaves, classification and solid-liquid separation.

Amanda and Jon Wills opened the conference this morning, welcoming our 50 delegates from 13 countries, and thanking our sponsors, Hudbay Minerals, Gravity Mining and Steinert, our Media Partners International Mining and Imformed, and Industry Advocates the Coalition for Eco-Efficient Comminution (CEEC), the Cornwall Mining Alliance and the Critical Minerals Association.

Amanda explained that we had to commit to an online event some time ago due to the pandemic, but previous physical separation conferences have been held in Falmouth, where we hope to be back in 2 years time. Cornwall is the most appropriate venue for these events, as the county is regarded as being the birthplace of modern mining, and in its 19th century heyday the tin and copper miners upgraded their ore by physical methods, gravity concentration and hand sorting, the only methods available at that time. These methods began to fail as the ores mined became leaner and more finely grained, and froth flotation came to the rescue in the early 20th century.

Gravity concentration has, however, over the past few decades enjoyed a strong revival, with the development of enhanced gravity machines allowing the treatment of finer grained ores. There is also a strong awareness that gravity concentration is more environmentally friendly than flotation, and is cheaper and simpler. Improvements have also been enhanced by more efficient classification methods and we were fortunate to have Kevin Galvin, Laureate Professor at the University of Newcastle, Australia, the inventor of the Reflux Classfier, open the first technical session, Gravity Concentration, with a keynote lecture "New challenges for gravity concentration and classification of fine particles" (see posting of 7th February 2022).

Kevin Galvin (right) at Physical Separation '19, with Stuart Saich of Promet101

Following Kevin's keynote were six presentations from Australia, Canada, France, South Africa and Turkey.

Mineral processing flowsheets that include gravity concentration typically utilise significant quantities of energy and water for materials transport and optimum metallurgical performance. These flowsheets are prime candidates to benefit from innovative approaches to lower water consumption. Edward Hart, of Mineral Technologies, Australia, described a proprietary surge bin design that has recently demonstrated suitability in upgrading minerals by rejection of fine/low specific-gravity particles and in addition allowing pumping of high pulp density slurries that were previously not considered practical.

Water-pulsated jigging is one of the earliest methods of gravity concentration but, as explained by Mahmut Camalan, of the Turkish Energy Nuclear and Mineral Research Agency, the process is adversely affected if drag forces cause particles to fall at constant or terminal velocities and he proposed two methods, sample preheating and polymer addition to the jig water, to reduce drag forces, sample preheating enhancing separation at low to moderate pulsation, and polymer addition at moderate to fast pulsation.

Falcon SB concentrator

Over the years innovations in gravity concentration have allowed the treatment of much smaller particles than in the past and enhanced gravity devices have become standard equipment in most gold recovery processes because they are a simple, inexpensive, and effective way of recovering free gold. The Falcon Concentrator is one such device and Sepro Systems of South Africa has developed a new centrifuge bowl that significantly improves gold recovery from grinding circuits. Wynand Erasmus described the evolution of the Falcon gravity concentrator from inception to present day and presented a case study illustrating the gold recovery improvements of the new Sepro Frontier™ bowl at the pilot and industrial plant scale.

Gillian Omaga, of Université de Lorraine, France, described the use of a Falcon Concentrator to recover critical metals as by-products of lithium processing from a rare-metal granite. The application of a Selfrag high-voltage electric pre-treatment stage before grinding increased the performance of the separation. 

Numerical and experimental invesigations on a Falcon Concentrator were performed at the University of British Columbia, Canada, using a fully coupled numerical model for slurry flow, which  was developed to be generalisable for dense slurry flows. Utkan Caliskan compared the numerical results to the experimental results obtained on a lab-scale Falcon L40 unit.

Franco van der Venter, of Gravitas Minerals, South Africa, described the Optima Classifier™, a multi-commodity hindered settler, which separates fine minerals based on density. The beneficiation of fine coal, chrome and iron ore was evaluated in this study. It was found that the Optima Classifier™ was able to produce market specific products in a single stage for all commodities evaluated. It was also found that using the Optima Classifier™ to beneficiate fine minerals is not only economically feasible, but also reduces the environmental impact of fine mineral disposal.

Optima Classifier

Following the mid day break were three presentations on Plant Practice.

Much of the remaining iron ore resources in Brazil consist of low-grade itabirite, which are currently processed in complex circuit flowsheets. Accordingly, a typical industrial itabirite circuit would include a four-staged crushing/screening plant, followed by grinding in a closed-circuit ball mill, desliming in hydrocyclones and final ore mineral concentration in reverse flotation circuits. In recent years Vale implemented various initiatives for investigating alternative processes towards simplified flowsheets. Accordingly, the proposed disruptive flowsheet consists of a primary crushing stage, SAG milling, primary concentration using Vertically Pulsating High-gradient Magnetic Separation, and a final concentration stage using the Reflux Classifier. The inventor of the Reflux Classifier, this morning's keynote speaker, Kevin Galvin, described such a circuit, which would eliminate several unit operations, by excluding secondary to quaternary crushing, desliming stages, complex flotation circuits, thickening and the flotation reagent plant. 

Artisanal gold mining is based on empirical methods which reduce the efficiency of concentration processes and increase their environmental impact. Flor Granda-Arce, of Universidad de Ingenieria y Tecnologia, Peru, described the use of a water-only cyclone (WOC) for the concentration of valuable heavy minerals from placer deposits in Madre de Dios, one of the richest (and most affected) areas in the Amazon basin. The presentation highlighted the potential of using WOCs as an environmental alternative for the processing of placer deposits in this region and the specific behaviors for different minerals, especially those carrying rare earths (Ce, La) and transition metals (Zr, Ti).

The concentration and transportation of ore, concentrates, or tailings are two common challenges mining companies today. Mining companies are seeing lower available valuable metals or minerals with an increased gangue-minerals concentration which makes handling of slurries more difficult. Difficulties in handling of slurries can lead to a reduction of a mill's working life due to the filling of tailings ponds, or there can be difficulty in filtration of tailings or concentrates or pumping ore that has been slurried over long distances in pipelines. While synthetic polymers are necessary to achieve faster liquid-solid separation rates, polymers can impart negative rheological characteristics to slurries. In the final presentation of the day Lawrence Andermann, of Suez Water Technologies & Solutions, USA, discussed methodologies for measurements of rheological properties of various kinds of slurries; such as viscosity, slump tests, Marsh Funnel, and Vane Rheometry.

All of the conference presentations are available on demand, so it is not too late to register.

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