The importance of coarse particle rejection in reducing water and energy consumption

In my keynote lecture at last month's IMPC Asia Pacific Conference I highlighted the importance of ScienceDirect in the evolution of Minerals Engineering journal. Analysis of the huge number (around half a million per year) of downloads from ScienceDirect showed that in recent years the most sought after papers were those involved with sustainability, particularly the growing need to conserve water and reduce energy consumption.

In my early years in mineral processing little thought had been given to water conservation, apart from recycling where possible, and although it was well known that mineral processing, particularly comminution, was a massive consumer of energy this was just accepted as a fact of life and no real efforts were made to attempt to minimise consumption. 

Now it is realised that conservation of water and energy is not just desirable, but is essential, and every effort is being made to mitigate consumption in these areas. Rejection of gangue at as coarse a size as possible is critical and is now an area for intensive research and innovation.

Preconcentration within the crushing circuit aims at reducing the amount of material fed to the energy-hungry grinding circuit, and heavy medium separation has been used for years on ores which are amenable to this, such as tin and lead-zinc ores, and coal. The range of ores which can be preconcentrated has been dramatically increased in recent years with the development of sensor-based electronic sorting, a completely dry process originally used for the concentration of diamond ores, but now being used in many other areas, due to modern sensors which can rapidly detect a range of physical properties, including grade of particles.

Typical electronic sorter

High Pressure Grinding Rolls (HPGR) have found favour for fine crushing, replacing tertiary cone crushing and rod milling, while stirred mills, introduced into the minerals industry to provide the need for ultra fine grinding, have replaced ball mills for many fine grinding duties. It is interesting that in recent years HPGRs have been used to grind finer while stirred mills are taking coarser and coarser feeds, replacing ball mills, which have always been known to be inefficient users of energy. Could it be that in future there will be an overlap in the product from HPGRs and the feed to stirred mills, and tumbling mills, including the SAG mill, will become obsolete?

In his forthcoming keynote lecture at Comminution '23, Prof. Arno Kwade, of Technische Universität Braunschweig, Germany will show how dry operation of stirred media mills has recently come into focus for the minerals industry, and maybe the comminution circuit of the future might be totally dry, with water being added only at the subsequent concentration stage.

A comminution circuit of the future?

Flotation is the dominant concentration method, and in my early years with Minerals Engineering, flotation research was targeted at the treatment of fine particles. In contrast, flotation at coarse sizes has become a recent focus for research and innovation.

Eriez is a regular sponsor of MEI's flotation conferences, and is one of the sponsors of Flotation '23 in Cape Town next year. One of Eriez’s products is the HydroFloat® Separator for coarse particle mineral concentration, which delivers the capacity of a density separator while maintaining the selectivity of a flotation device. Using a novel aeration system to disperse fine bubbles into a fluidised-bed environment, the HydroFloat® Separator significantly increases the selective recovery of coarse particles by applying flotation fundamentals to gravity separation, reducing water and energy consumption and producing safer tailings.

I was pleased to hear that last month Weir Minerals, a sponsor of Sustainable Minerals '22 announced a cooperative agreement with Eriez to design and develop coarse particle flotation systems. This cooperation allows both companies to better connect the Eriez equipment  with the slurry classification and conveying expertise of Weir Minerals.

A leading player in the development of coarse flotation systems has been Prof. Graeme Jameson, the inventor of the Jameson Cell, and one of his recent inventions, the Novacell, is said to be a breakthrough in flotation equipment technology, a "Universal" machine which provides efficient coarse and fine particle flotation in one device.

The HydroFloat Separator and the Novacell

It is great to see our industry, once so conservative and reluctant to change, embracing new areas of research and development.

@barrywills