Technological breakthroughs

Iranian researchers combined flotation experiments with the TOPSIS decision-making model to identify a collector blend that delivers both high recovery and favorable cost and supply advantages.

A research team at Amirkabir University of Technology (Iran) has developed a method for selecting the optimal collector for apatite ore by combining flotation experiments with the TOPSIS multi-criteria decision-making model.

The approach allows technical performance, cost, and supply availability of different collectors to be evaluated simultaneously, rather than choosing a collector based solely on laboratory recovery rates.

Phosphate ore is getting harder to process

Apatite is one of the most important phosphorus-bearing minerals, used as a raw material for phosphate fertilizers as well as various industrial and pharmaceutical products.
Demand for phosphate continues to rise alongside agricultural intensification and fertilizer production. At the same time, high-quality phosphate resources are under growing pressure, while low-grade, impurity-rich ores are increasingly being mined.

Global phosphate resources are also concentrated in a handful of countries, including Morocco, China, Russia, and the United States. This makes improving ore-processing efficiency — particularly for low-grade sources — an important priority for the phosphate industry.

Flotation is one of the most common methods used to upgrade apatite ore. However, conventional flotation processes typically rely on fatty acids as collectors. For ore containing significant impurities such as silicates, carbonates, and iron oxides, using a single collector often fails to achieve the desired selectivity and recovery.

Testing on tailings from the Chadormalu mine

To find a suitable solution, the research team used ore samples taken from the tailings of the Chadormalu magnetite-hematite mine in Yazd Province, Iran. This ore has a relatively low phosphorus content, with a P2O5 grade of about 8.49%.

Experiments were conducted at two scales. At laboratory scale, the team used micro-flotation with a Hallimond tube on a purified apatite sample to compare various collectors across different pH levels. The best-performing collector from this stage was then tested at bench scale using a Denver D-12 flotation machine on an actual ore sample, in combination with eight different secondary reagents.

A range of surfactants from different classes — including anionic, nonionic, and ethoxylated compounds — were included in the tests.

Results showed that a combination of Tall Oil Fatty Acid (TOFA) and a six-mole oleic acid polyethylene glycol ester (OAPEGE6), designated by the team as TO6, achieved the best apatite recovery.

Under alkaline conditions, at a pH of around 9.5, the recovery rate reached approximately 92%.

When testing moved to the actual ore sample, a 70:30 blend of TO6 and diesel fuel continued to stand out. This formulation achieved a recovery rate of 91.1%, a P2O5 grade of 22.2% in the concentrate, and a separation efficiency of 69.9%.

This was the best result among the eight formulations tested.

Several other formulations — TO6 combined with kerosene or with ethoxylated nonylphenols (ENP6, ENP10) — also performed reasonably well, though not as strongly. Meanwhile, the formulation paired with sorbitan monooleate (Span 80) had the lowest separation efficiency among the eight formulations, at just 35.9%.

Recovery rate alone isn't enough

According to the research team, however, the formulation that performs best in the laboratory is not necessarily the best choice for production.

This is why the team applied TOPSIS (Technique for Order Preference by Similarity to Ideal Solution), a multi-criteria decision-making method used to rank alternatives based on how closely they approach an "ideal solution."

The model evaluated five criteria: P2O5 grade, recovery rate, separation efficiency, collector cost, and market availability.

To limit subjectivity, the weight assigned to each criterion was determined using the Shannon entropy method, rather than relying entirely on expert judgment.

The results showed that market availability and cost carried the greatest weight in the decision, at 0.462 and 0.298 respectively, while technical indicators such as grade and recovery carried lower weights.

According to the research team, this reflects an important issue in real-world production: a high-performing collector that is expensive or difficult to source reliably is not necessarily the optimal choice for a plant.

TO6-diesel comes out on top

After combining all five criteria, the TO6-diesel formulation achieved the highest closeness score to the ideal solution, with an RC value of 0.9983, and was ranked as the optimal formulation.

The next-ranked formulations were TO6-ENP6 (RC 0.8845), TO6-ENP10 (RC 0.8570), and TO6-kerosene (RC 0.8004). At the bottom of the ranking was TO6-EIT (ethoxylated isotridecanol), with an RC of just 0.0355 — due to very limited market accessibility, even though its separation efficiency (43%) was not the lowest among the eight formulations on technical grounds alone.

A notable aspect of the study is that the selected formulation was not chosen based on apatite recovery alone, but also accounted for factors with direct relevance to plant operations, including cost and raw material availability.

Potential for other ore types

The research team suggests that the combined flotation-and-TOPSIS framework could be applied to other ore types and collector systems as well.

Rather than testing each formulation in isolation and choosing based mainly on a few technical indicators, this method provides an integrated evaluation framework that balances processing efficiency with economic feasibility.

Still, before industrial-scale application, the team says further comprehensive economic assessments are needed, along with life cycle environmental analysis of the collectors involved. This would provide the basis for identifying not just high-performing formulations, but ones that are also cost-effective and lower in environmental impact.

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