Technological breakthroughs

Apatite-bearing iron ores represent a potential dual raw material source for both the metallurgical industry and fertilizer production. However, the simultaneous extraction of these two valuable minerals from the same ore source remains highly challenging due to the complex mineralogical composition and the close association between mineral phases. A recent study applied a combined approach of low-intensity magnetic separation and flotation to recover both magnetite and apatite from Bingöl ore, Turkey.

With the global development of industry and technology, the demand for iron and steel has increased significantly. Reserves of high-grade iron ore that can be directly used in iron and steel production are being rapidly depleted. At the same time, the preparation of iron ore concentrates that meet the technical requirements of the steel industry has become essential. Physical separation methods such as gravity separation, magnetic separation, and flotation are standard techniques used to remove gangue minerals from iron ores.

Phosphorus Challenge in Iron Ore

Phosphorus is a critical impurity in iron ore, and almost all phosphorus present in iron ore is transferred directly into hot metal during the metallurgical process. Steel with high phosphorus content is typically brittle and prone to cracking; therefore, the removal of phosphorus from iron ore is an important research topic. The only effective way to control phosphorus content in metal is to limit the amount of phosphorus in the ore. Steel-producing countries generally recommend that the phosphorus content in iron ore should be below 0.1%, although this limit may vary by country.

The removal of phosphorus from certain iron ores is particularly difficult, especially when phosphorus-bearing phases are complexly associated with iron phases. Nevertheless, phosphorus can be removed from iron ore through physical processes such as magnetic separation, flotation, and selective agglomeration, or through chemical processes including leaching, thermal treatment, and biological methods.

On the other hand, phosphorus is a common element in the Earth’s crust and is found in all living organisms. More than 200 phosphate minerals occur in the Earth’s crust, and structurally all contain the tetrahedral (PO₄) unit. Approximately 95% of global phosphate rock production is consumed in fertilizer manufacturing. The principal phosphate mineral is apatite, with the chemical formula Ca₅(PO₄)₃(F, Cl, OH, CO₃), including fluorapatite, chlorapatite, hydroxylapatite, and carbonate-hydroxyl-apatite.

Characteristics of the Studied Ore

This study used apatite-bearing iron ore samples from the Bingöl region of Turkey. Magmatic and metamorphic phosphate deposits such as Bingöl-Genç (Avnik) and Bitlis-Ünaldı are highly complex and mainly consist of magnetite and apatite, together with silicates such as amphibole, epidote, diopside, and chlorite, and carbonates such as calcite, dolomite, siderite, and ankerite. The main problem associated with Bingöl–Bitlis ores is their high phosphorus content.

Chemical analysis showed that the run-of-mine ore contained 35.75% Fe and 5.36% P₂O₅. The results indicate that the ore is iron-rich, with phosphate and silicate minerals as the main gangue phases. The raw ore cannot be directly used in the iron and steel or fertilizer industries and must be upgraded using appropriate beneficiation methods.
X-ray diffraction (XRD) analysis identified the main mineral phases as apatite, magnetite, quartz, feldspar, calcite, dolomite, ilmenite, barite, rectorite, and muscovite. These minerals are typical of phosphate-bearing iron ore deposits.

Ore Beneficiation Process

The study applied a combined magnetic separation and flotation process to recover both magnetite and apatite. The raw ore was ground to a particle size below 106 micrometers, followed by magnetic separation consisting of two cleaning stages and one rougher stage. The non-magnetic product was then subjected to flotation with three cleaning stages and one rougher stage.

Magnetic separation was carried out using a low-intensity wet drum magnetic separator operating at a drum speed of 25 rpm and a pulp density of 10% solids by weight. This process increased the Fe grade from 35.75% to 63.55% with a recovery of 80.40%. However, the magnetite concentrate still contained 1.65% P₂O₅, a phosphorus level exceeding the acceptable limit for the iron and steel industry.

XRD and SEM-EDS results showed a strong increase in magnetite peak intensity in the magnetic product, although other minerals such as apatite were still present. EDS analysis indicated that Fe accounted for up to 95.95 wt.% in the magnetic product. However, SEM observations revealed that particles containing a single liberated mineral phase were very rare, indicating poor mineral liberation due to the intimate association between magnetite and phosphate mineral phases.

Apatite Flotation

The non-magnetic product (magnetic separation tailings) was subjected to flotation to recover apatite. Particle size analysis showed a d₅₀ of approximately 80 micrometers with a relatively narrow size distribution, which may have a positive effect on flotation performance.

A direct anionic flotation process was applied using industrial tall oil fatty acid as the collector at a dosage of 800 g/t. Sodium metasilicate was used as a dispersant to disperse silicate gangue minerals. Corn starch was used as a depressant for iron minerals at a dosage of 1,000 g/t. MIBC was used as a frother at a fixed dosage of 30 g/t. NaOH was used to adjust the pulp pH to 9.5.

Flotation results showed a significant improvement in P₂O₅ grade in the phosphate concentrate. A phosphate concentrate containing 25.33% P₂O₅ was obtained with a recovery of 64.89%. However, the relatively high iron content (6.45% Fe) indicated that iron-bearing minerals were still present in the concentrate.

XRD analysis confirmed that apatite minerals were enriched in the flotation concentrate, with a strong increase in apatite peak intensity after flotation. However, although flotation significantly reduced the magnetite reflections, they never completely disappeared.

EDS analysis of the flotation concentrate showed that the combined distribution of Ca and P elements reached 83.89 wt.%, much higher than that of other elements. This indicates that phosphate minerals such as apatite were the dominant mineral phase in the flotation concentrate, although small amounts of silica and other mineral phases such as iron oxides were also present.

Limitations to Be Addressed

Although the study achieved some positive results, several challenges remain. The magnetite concentrate still contained a high phosphorus content (1.65% P₂O₅), which is unacceptable for the iron and steel industry. The phosphate concentrate had a relatively low P₂O₅ grade (25.33%) for a commercial phosphate product, while the Fe content (6.45%) remained too high for the fertilizer industry.

The main reason for these limitations is the complex mineralogical composition of the ore, particularly the close association between Fe oxides and phosphate minerals, and the poor mineral liberation. When magnetite is intimately associated with phosphate minerals such as apatite, these composite particles tend to float (into the concentrate or middlings) or sink (remaining in the tailings) depending on flotation conditions. Locked mineral particles represent the most significant obstacle to selective flotation, and their behavior during flotation is extremely difficult to predict.

Conclusions and Future Directions

The study demonstrated the feasibility of simultaneously enriching both iron and phosphate from apatite-bearing iron ore by combining low-intensity magnetic separation and flotation. This approach enables the recovery of two valuable products from a single ore source, contributing to improved utilization efficiency of mineral resources.

The results showed that magnetite in the ore can be upgraded using low-intensity magnetic separation, while apatite can be enriched from the non-magnetic product by flotation. However, to obtain higher-quality iron and phosphate concentrates, further studies are required on the mineralogical characteristics of the ore, improvement of mineral liberation through optimized grinding processes, and adjustment of technical parameters in magnetic separation and flotation.

The successful recovery of both iron and phosphate from these deposits would significantly contribute to maximizing the value of the ore resources, in line with sustainable development and circular economy trends in the mining and mineral processing industry. This also represents a promising research direction for similar complex ore resources in Vietnam and the region.

Source:
Birinci, M. (2021). Enrichment of Apatite-Bearing Iron Ore by Magnetic Separation and Flotation. European Journal of Technique, 11(1), 1–6.