Found in smartphones, modern cars, climate-friendly photovoltaic units and used in many other industries, hi-tech materials have become an indispensable constituent of everyday life. Although recycling can partially cover the demand for raw materials, most are still sourced from mining. The environmental impacts are well known: land use, the generation of additional traffic infrastructure and the industrialization of often remote areas. Mining also requires vast quantities of water and produces correspondingly large volumes of wastewater. Working in partnership with colleagues in Finland, a team of researchers at HIF led by process engineer Bruno Michaux has developed a method of making water usage in the processing of mineral raw materials more sustainable. Taking the mineral fluorite as an example, they have shown how the water consumption can significantly be reduced by the aid of process simulation.
Fluorite – also known in mineralogy as fluorspar and by its chemical name of calcium fluoride – is an important raw material for industry. It is used, for example, in the smelting of iron, in aluminum extraction and in the chemical sector as a raw material for producing fluorine and hydrofluoric acid. Probably the best-known product of fluorine chemistry is PTFE, a fluoropolymer which is sold in membrane form under the trade names Teflon and Gore-Tex.
Ore beneficiation as a water guzzler
“The extraction of fluorite consumes a lot of water,” explains Bruno Michaux. “Depending on the local climate, but even more so on the design of the mineral beneficiation plant, it can be up to 4,000 litres per tonne of ore.” There is obviously nothing that the HIF researchers can do about the weather, but they can certainly contribute to optimizing the processing itself. In this step of the process, waste rock is separated from the extracted ore in order to raise the fluorite content from below 50 percent to around the 98 percent mark. To accomplish this, the engineers apply the flotation process. In simple terms, it works as follows: the ore is ground and mixed with plenty of water; then various chemicals are added to the mixture to render the fluorite surface water-repellent (hydrophobic). Air is then pumped into said mixture, creating small bubbles that carry the hydrophobic particles to the surface. The fluorite thus accumulates in the resulting foam while the waste rock is left behind. Before the latter can be deposited on a waste dam or returned underground as a filling material, a dewatering step is needed. In order to achieve the desired concentration of fluorite, flotation is repeated several times, which consequently requires a lot of water.