Technological breakthroughs

A research team at Amirkabir University of Technology in Tehran, Iran, has developed an approach that combines flotation experiments with a multi-criteria decision-making model to identify the most suitable combination of flotation reagents for apatite ore. The method considers not only mineral recovery performance but also reagent cost and market availability.

The study was conducted using tailings samples from the Chadormalu mine in Iran and was published in Scientific Reports.
From Low-Grade Ore to Reagent Selection
Apatite is a phosphate-bearing mineral and an important raw material for fertilizer production. However, many apatite ore deposits contain relatively low concentrations of valuable minerals and are associated with impurities such as silicates, limestone and iron oxides.

In such cases, using a single flotation reagent, or collector, is often insufficient to achieve the desired performance. Processing plants may therefore need to combine several chemicals to improve apatite recovery and increase the phosphorus content of the concentrate.

However, selecting the right reagent combination is not straightforward. Different chemicals have different advantages and disadvantages in terms of flotation performance, cost and availability. In practice, such decisions often rely heavily on experience and experimental results.

The researchers proposed a more quantitative approach by combining laboratory flotation tests with TOPSIS, a multi-criteria decision-making method widely used in engineering and management.

Screening a Range of Reagents

The ore samples were collected from an iron ore tailings site at the Chadormalu mine, consisting mainly of magnetite and hematite, with a P₂O₅ content of approximately 8.5%.

The researchers conducted two stages of experiments.

In the first stage, six reagents from the fatty acid and hydroxamic acid groups were tested on relatively pure apatite samples using a Hallimond tube, a small-scale flotation device commonly used in laboratory studies. The experiments were conducted across a pH range of 4 to 11.

The results showed that a mixture of tall oil fatty acids (TOFA) and an oleic acid derivative containing an ethylene glycol chain, referred to as TO6, delivered the highest recovery, reaching up to 92%, particularly under alkaline conditions at around pH 9.5.

By contrast, most of the reagents performed poorly under acidic conditions, between pH 4 and 6. One exception was a hydroxamic acid reagent that retained its ability to interact with the mineral surface even at low pH.

TO6 and Diesel Deliver the Best Results

In the second stage, the researchers moved to larger-scale laboratory tests using actual ore samples.

TO6 was retained as the main component, accounting for 70% of the reagent mixture by weight, and was combined with eight different secondary reagents making up the remaining 30%. These included diesel, kerosene, ethoxylated compounds and several sorbitan-based surfactants.

The results showed significant differences among the reagent combinations.

The TO6-diesel combination delivered the strongest overall flotation performance, achieving a recovery rate of 91.1%. The P₂O₅ content of the concentrate reached 22.2%, while the separation efficiency was 69.9%.

The combination using kerosene produced broadly comparable results, although its performance was slightly lower.

Some combinations containing nonylphenol ethoxylates, such as ENP6 and ENP10, also achieved relatively high recovery rates. However, their concentrates contained lower P₂O₅ levels. The researchers also noted that previous studies have reported adverse environmental effects associated with these compounds, suggesting that alternatives should be considered for practical applications.

Meanwhile, combinations using Tween 80, Span 80 and several other reagents produced substantially lower separation efficiencies. In some cases, the efficiency was below 2%.

Turning Reagent Selection into a Mathematical Problem

Rather than selecting the best reagent combination based solely on a single indicator such as recovery, the researchers evaluated all eight combinations using the TOPSIS model.

The method simultaneously considered five criteria:

• P₂O₅ content in the concentrate;
• Recovery rate;
• Separation efficiency;
• Reagent cost;
• Market availability.

Market availability was scored on a scale from 1 to 5, ranging from very difficult to obtain to readily available.

To determine the relative importance of each criterion, the researchers used the Shannon entropy method. This statistical approach identifies criteria that show greater variation among the alternatives and therefore have greater discriminatory power in the final ranking.

The results showed that reagent availability, with a weight of 0.462, and cost, with a weight of 0.298, had the greatest influence on the final selection. Both factors were assigned greater weights than technical indicators such as concentrate grade and recovery.

After comparing the distance of each option from the ideal and worst-case solutions, the model produced the following ranking:

1. TO6-diesel: 0.998, ranked first;
2. TO6-ENP6: 0.885;
3. TO6-ENP10: 0.857;
4. TO6-kerosene: 0.800;
5. TO6-Tween 80 and TO6-Span 80: approximately 0.69-0.71;
6. TO6-N-oleoyl sarcosine: 0.306;
7. TO6-ethoxylated isotridecanol: ranked last because of its low separation efficiency and limited availability.

The TOPSIS results were broadly consistent with the indicators obtained from the flotation experiments. Diesel, in particular, benefited from its relatively low cost and widespread availability.

Looking Beyond the “Best” Chemical

According to the researchers, the main contribution of the study is not the discovery of an entirely new flotation reagent but the development of a systematic approach to selecting reagent combinations.

Instead of asking only which reagent delivers the highest recovery, the new approach considers several questions simultaneously: How effective is it? How much does it cost? Is it readily available? And which option offers the best overall balance?

This approach could help mineral processing plants make more data-driven decisions rather than relying entirely on experience or a single technical indicator.

However, the researchers emphasize that further evaluation is needed before the method can be applied on an industrial scale. Areas requiring further study include a more comprehensive economic assessment, the environmental impacts and life cycles of the selected reagents, and the reproducibility of the results in pilot-scale or industrial-scale testing.

If validated under real operating conditions, combining flotation experiments with multi-criteria decision-making tools could provide a useful method for optimizing reagent formulations in mineral processing plants, particularly when dealing with low-grade ores with complex compositions.

Source: Abdollahi, S., Afraei, S., Irannajad, M. (2026). “A technical–economic framework for selection of optimal collector combinations in apatite flotation via TOPSIS multi-criteria decision-making”. Scientific Reports, 16, 19420.