Eco-friendly flotation method increases mineral yield

Flotation is one of the most important processes for separating minerals in the raw materials industry. Achieving the highest possible mineral enrichment requires the appropriate selection and dosage of reagents—a complex, time-consuming and cost-intensive procedure.

Researchers at the Helmholtz Institute Freiberg for Resource Technology (HIF), which is part of the Helmholtz-Zentrum Dresden-Rossendorf, have developed a workflow for the economic and ecological optimization and upscaling of flotation reagents. Initial tests on an industrial scale have shown a significant increase in the concentration of valuable minerals and confirmed the effectiveness of the developed approach.

The paper is published in the journal Colloids and Surfaces A: Physicochemical and Engineering Aspects.

Within the flotation process, gas bubbles are added to a liquid with finely ground particles, and the bubbles adhere to particles with a water-repellent surface. These rise to the top with the attached air bubbles and form a froth layer that can be skimmed off. Mineral particles have different surface properties, but it is the selectively adsorbing reagents that determine to which particles gas bubbles can adhere.

Various reagents—substances that trigger a reaction if contacted with certain other substances—are used to increase the efficiency of particle separation. However, quantifying the potential of new reagents in industrial flotation processes is very costly and time-consuming.

“Flotation reagents are crucial for enrichment efficiency. Our knowledge about their effect has often only been based on laboratory-scale experiments. The selection and dosing of reagents has often been informal, subjective and empirical, based on experience. However, a reagent system consists of several components whose interactions are complex.

“Simply replacing a reagent therefore rarely leads to the desired success. Instead, factors such as dosage, application method and interactions with other reagents and minerals must be taken into account,” says HIF doctoral student Borhane Ben Said, explaining the challenges.

New workflow successfully tested on an industrial scale—Spin-off in preparation

In the CoSilFlot project, Ben Said investigated the selective separation of scheelite and calcite using colloidal silica as a reagent. The experiments were statistically planned, numerically optimized and digitally processed so that a large number of flotation tests could be ruled out at an early stage and the optimum dosage ranges of the single reagents on an industrial scale were quickly determined.

The methodology was successfully tested in an industrial flotation plant in Europe, where an increase in the valuable mineral content of up to 16% was achieved. “This underlines the enormous potential of our workflow.

“We are currently working on various case studies in the follow-up project CoSilFlot+, including the replacement of highly toxic hydrofluoric acid with sodium fluoride in feldspar flotation and the implementation of biopolymers for the separation of chalcopyrite and molybdenite,” says Ben Said, describing the next steps.

The results offer a good utilization opportunity for mining companies and manufacturers of flotation reagents, as the companies can respond better to changes in the case of complex mineral compositions. The flexibility is also advantageous for the implementation of environmentally friendly flotation reagents, as the mining industry is dependent on ecologically compatible reagents in the future. In addition, the workflow offers good prospects of being spun off as a company.

“Following successful validation, we plan to establish a spin-off that will offer the CoSilFlot+ workflow as an engineering service for mining companies and chemical manufacturers. The aim is to bring both players together to develop efficient and environmentally friendly solutions and further optimize process results.

“At the same time, manufacturers of flotation reagents can open up new applications for their products and thus improve their market opportunities,” says Ben Said.