Mar 29 2019
It is a well-known fact that water is an important resource that is depended by a large number of industries and one that can be used more frugally.
Plenty of water is needed for mineral processing. (Image credit: HZDR/Detlev Müller.)
The beneficiation of mineral ores is one example of that. Now, considering the raw material fluorite as a case in point, scientists at Helmholtz Institute Freiberg for Resource Technology (HIF) have demonstrated how the use of water can be improved. The team devised a novel process that prolongs the replication of the beneficiation process. It specifies the conditions in which it would be viable to recycle water without incurring significant losses at the time of ore enrichment. As a result, the usage of fresh water can be considerably cut down. Such an approach would not only benefit the environment but it would also prove useful for the mining companies, since it makes it more efficient to extract raw materials. The team has described the novel process in the Journal of Environmental Management. Part of Helmholtz-Zentrum Dresden-Rossendorf, HIF now works closely with TU Bergakademie Freiberg.
Hi-tech materials can be found in climate-friendly photovoltaic units, contemporary cars, and smartphones and also employed in a host of other industries. These materials have turned out to be a vital part of day-to-day life. While recycling can partly meet the requirement for raw materials, a majority of these materials are still obtained from mining. The impacts caused to the environment are well known—the industrialization of remote regions, the creation of extra traffic infrastructure, and land use. In addition, mining also needs huge volumes of water and correspondingly generates large quantities of wastewater. Now, working closely with coworkers in Finland, a research team at HIF, headed by process engineer Bruno Michaux, has created a new method through which the consumption of water required for processing mineral raw materials can be made more sustainable. Taking the fluorite mineral as a case in point, the researchers have demonstrated how the usage of water can be considerably decreased with the help of process simulation.
In mineralogy, fluorite is also called fluorspar and is usually referred by its chemical name of calcium fluoride. It is considered to be a vital raw material for industry, and is utilized, for instance, in aluminum extraction, in the smelting of iron, and in the chemical industry as a raw material for making hydrofluoric acid and fluorine. Perhaps, PTFE, a kind of fluoropolymer, is the most popular product of fluorine chemistry. It is sold in a membrane form typically under the trade names Gore-Tex and Teflon.
Ore beneficiation as a water guzzler
The extraction of fluorite consumes a lot of water. 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.
Bruno Michaux, Process Engineer, Helmholtz-Zentrum Dresden-Rossendorf
Evidently, the HIF scientists cannot do anything about the weather, but they can definitely help in improving the processing itself. In this procedural step, waste rock is first isolated from the extracted ore so as to increase the fluorite content from less than 50% to close to the 98% mark. The engineers accomplished this by applying the flotation process. In other words, it operates in the following way: the ore is initially powdered and combined with a lot of water; numerous chemicals are then added to the resultant mixture to make the surface of the fluorite water-repellent (hydrophobic). Next, air is pumped into this mixture, which produces tiny bubbles that transmit the water-repellent particles to the surface. Therefore, the fluorite builds up in the ensuing foam, leaving behind the waste rock. A dewatering step is required before depositing the waste rock on a waste dam or returning underground as a filling material. To realize the required concentration of fluorite, a flotation process is repeated a number of times, which accordingly needs plenty of water.
Mining companies are trying to reduce their consumption of water by using it multiple times. However, used water contains substances that can interfere with the process performance, and that is something to be avoided.
Bruno Michaux, Process Engineer, Helmholtz-Zentrum Dresden-Rossendorf
Magnesium and calcium ions are examples of such substances, which tend to obstruct the hydrophobization of the surface of fluorite. The concentration of the ions decides the potency of this effect. In the latest approach, the effect of water’s chemical composition on the flotation is taken into consideration. Owing to elaborate lab experiments conducted on a fluorite ore, the team achieved data that reflected the intricate interaction of the dissolved substances and subsequently incorporated them into the HSC Sim simulation software. The mining industry is already using this software for mapping the processing plant and for controlling the mineral beneficiation process.
Digital monitoring of water and energy consumption
“With the additional features we developed, the software is now able to take into account the composition of the process water,” Michaux explained. “This enables the possibility of recycling the water without compromising the process efficiency.”
In addition, the simulation enables operators to improve the usage of varied water reservoirs close to the mine like aquifers, sea, rivers, or lakes. Additional process steps, like the grinding and dewatering of the ore, have to be incorporated in the coming days. In an ideal situation, the consumption of water may subsequently fall below 1,000 L per ton of ore.
The researchers are hoping to apply this novel technique to a practical test in a real mining operation quite soon.
As this requires a fully digitized treatment process in which sensors are continuously measuring and reporting the properties of the streams to process control, it is only larger mines that will venture such an investment at this early stage. The potential of digitization is, however, enormous: real-time monitoring and truly intelligent process simulation make it possible to extract more raw materials while using less energy and fewer natural resources.
Bruno Michaux, Process Engineer, Helmholtz-Zentrum Dresden-Rossendorf
This also applies to ores, apart from recycling the water in fluorite processing, for which the simulation technique was devised by the HIF researchers.