Modern Mining June 2023

of electricity savings and reduced environmental impact, ie, doing more with less. GoldOre’s environmental solutions A little-known application of the MACH is in the field of environmental remediation where it is used to enhance sodium metabisulphite (SMBS)/Air or sul phur dioxide (SO 2 ) /Air systems where the power of cavitation is harnessed within the venturis of the MACH to improve mass transfer. Cavitation (which is the rapid formation and implosive collapse of voids within a fluid) supports free radical chemistry – also a key mechanism of SMBS/Air systems – so it makes sense that the two technologies would marry well together. The MACH may also be used for arsenic remediation by enhancing the precipitation of scoro dite-like compounds, which research has shown to have long-term stability on tailings dams. Last, but not least, there is the field of water treatment where the MACH may be used to treat acid mine drainage, for example. Apart from saving power by bring ing efficiency to these systems, the environmental applications of the MACH significantly reduce a mine’s overall impact on the environment, paving the way for a more sustainable future. Research-driven power optimisation Having established the effectiveness of the MACH to improve both extraction kinetics and recoveries, GoldOre turned its attention to optimising the power consumption of the MACH. This entailed revisiting the initial design criteria and systematically eliminat ing anything that was a nice-to-have. It took many years of research to understand the critical components within the MACH and to enhance these whilst simultaneously streamlining the design. Collectively, the design tweaks, together with the adjustment of operating parameters such as pressure and venturi speeds, resulted in a massive reduction in the power requirement of the MACH – by as much as 70 to 80% while maintaining metallurgical perfor mance. By comparison, the MACH draws around 50% less power than rival shear reactors on the market. This is enabled by the cavitation effect in the ventu ris, which requires a lower back-pressure, and hence also a lower power draw, when compared to compet itive systems. The metallurgical benefits of cavitation remain unmatched by rival shear reactor systems. Careful work was done to maximise the self aspirating abilities of the MACH in order to lower the pressure requirements of gas that is dosed into the reactor. Whereas existing systems in industry require gas pressures as high as 10 bar in order to operate effectively, the MACH is able to operate at highest efficiency with gas injection pressures as low as 1 bar. Given that much power is required to oper ate compressors to achieve high gas pressures, the lower gas pressure requirement of the MACH goes a long way to reducing overall power consumption.

The MACH is not a mill Another interesting phenomenon in minerals processing is particle breakage and liberation improvements, essential for effective mineral extraction, that can be achieved using the MACH, especially in multiple pass systems. This is owing to the energy release during cavitation – the centre of an imploding cavitating bubble can reach 5 500 0C and the water jet that splits the bubble will impact on a particle with a pressure of 1 000 atmospheres. This phenomenon can be put to good use by allow ing operations to coarsen mill grinds slightly, to achieve their final grind targets with the MACH at a lower overall energy consumption, whilst prepar ing the ore for downstream metallurgical processing through pico-bubble generation in the venturis of the MACH. Pico-bubbles enhance both leaching and flotation systems as well as any system where a gas is required to be dissolved into a liquid. As mills tend typically to be the highest power consumers on any metallurgical plant, any power savings on a mill operation will have a significant impact on overall power consumption. Technology that outlasts your operation Moreover, the MACH has been designed for longev ity – there are installed reactors in very abrasive environments that have required zero maintenance in over 10 years and are set to outlast the life of the operations in which they are installed. Unlike

The MACH reactor going through quality control checks.

June 2023  MODERN MINING  29