The cellulose-based compound developed by the team is renewable, biodegradable and non-toxic, and research shows that it could be more effective in separating metals than the oil-based commercial frothers currently used in flotation. The team has applied for a patent for the technology under the name of CellFroth.
Rodrigo Serna, a professor at Aalto University who came up with the idea, said that the chemical technology used in froth flotation has remained relatively unchanged for decades.
"We wanted to find more sustainable alternatives to these chemicals, so we started carefully exploring cellulose derivatives with properties considered suitable for frothers," he said. "It was quite surprising when, already in the first laboratory experiments, the new compound started to produce more minerals than traditional methods."
In the flotation process, air bubbles are created in a mixture of crushed ores, water and various chemicals. The metal-bearing minerals selectively attach to the bubbles, forming a froth on the surface from which they are collected. Frothers are required to control the formation and stability of air bubbles.
The current commercially applied frothers consist mainly of aliphatic alcohols and oligomeric glycol ethers. The new compound developed by the Aalto researchers is an aqueous polymer-surfactant mixture consisting of a nonionic amphiphilic polymer and a nonionic surfactant pair to be used as a flotation frother. The polymeric component of the mixture is a biodegradable cellulose derivative called hydroxypropyl methyl cellulose that is produced from sustainable sources.
The team found that their cellulose-based compound has several advantages over traditional frothers. They said it increases the amount of minerals recovered, while accelerating the flotation process, and also works efficiently in wider range of pH conditions, making it less sensitive to the changes in process conditions. In some cases, such as for zinc materials, the compound also helps reduce the need for chemicals in other aspects of processing.
This work builds on the researchers' past findings that tested the technology in a laboratory with minerals containing copper and zinc, and in continuous operation at a mini plant with ores containing copper. It has also been tested for the recovery of copper from waste streams, including mineral tailings and waste slag from metal refineries. The researchers are currently experimenting the technology with minerals containing gold.
The team's next step is to investigate commercialisation possibilities. According to the researchers, on an industrial scale the new technology could offer a higher production capacity in mineral processing plants and reduce the use of other chemicals. It can also handle waste streams with low contents of valuable minerals.
They also pointed out that in the future, as mineral resources deplete, the mineral processing industry must process larger amounts of low-quality ores to keep up with demand. Serna said: "The mining industry is under great pressure to develop more environmentally friendly practices. At the same time, they need to improve their productivity as the need for raw materials increases and the mineral reserves become depleted. These don't have to conflict with each other."
