Technological breakthroughs

Compiled by Bao Hien

A research team in China has published test results showing that a complex formed between xanthan gum — a natural polysaccharide — and iron ions (Fe3+) can play a dual role, acting as both a selective depressant and a selective flocculant, significantly improving the separation of ultrafine apatite from quartz through reverse flotation. This addresses a long-standing technical challenge in the phosphate mineral processing industry: handling the ultrafine ore fraction, which is becoming increasingly common as high-grade, easily processed deposits are depleted.

Why Ultrafine Particles Are a Difficult Problem

As high-grade phosphate deposits become increasingly depleted, the mining industry is being forced to turn to lower-grade ores with finer, more complex particle structures. In such ores, apatite — the valuable mineral — is often closely intergrown with gangue minerals like quartz at very fine particle sizes, making problems such as poor selectivity, low separation efficiency, and high reagent consumption increasingly prominent in conventional flotation processes.

Reverse flotation — where quartz is floated away while apatite is retained — is a widely used technique for removing silica from low-grade ore, and has been successfully applied in iron ore and magnesite processing. However, due to the lack of a truly effective reagent for the fine-grained apatite-quartz system, the application of reverse flotation for desilication of apatite ore has remained limited. Conventional modifiers — inorganic acids, phosphates, starch, and starch derivatives — typically show limited selectivity and effectiveness, particularly in ultrafine particle systems.

Mechanism: Combining Surface Hydrophilicity Preservation with Selective Flocculation

The research team — scientists from Wuhan Institute of Technology, Guizhou University, and Wengfu (Group) Co., Ltd. (one of China's major phosphate companies, home to a state key laboratory for efficient development of phosphorus resources) — tested the XG-Fe3+ complex at an optimal mass ratio of 1:9 (xanthan gum to FeCl3·6H2O), using dodecylamine (DDA) as the collector for quartz.

Results from multiple analytical techniques — contact angle measurement, zeta potential measurement, turbidity analysis, polarizing microscopy, and infrared spectroscopy — showed that the XG-Fe3+ complex operates through two complementary mechanisms. First, the complex chemically adsorbs onto the apatite surface, blocking DDA adsorption and preserving apatite's hydrophilicity — preventing apatite from floating with the air bubbles. Second, as a long-chain macromolecular reagent, XG-Fe3+ induces selective flocculation of ultrafine apatite particles through an adsorption bridging mechanism — increasing the apparent particle size of apatite and thereby reducing the mechanical entrainment of ultrafine particles into the froth during flotation. In contrast, the complex showed minimal interaction with the quartz surface, not interfering with DDA adsorption on quartz — allowing quartz to float normally.

Notably, the researchers found that xanthan gum alone, without combining it with iron ions, showed limited selectivity in the ultrafine apatite-quartz flotation system — indicating that the Fe3+ ion plays a critical role in unlocking the full effectiveness of this polysaccharide, consistent with prior research on the synergy between metal ions and polymer depressants.

Specific Experimental Results

In single-mineral tests at pH 8 (identified as the optimal condition), without XG-Fe3+, the flotation recovery difference between quartz and apatite was 41.27 percentage points. After adding XG-Fe3+ at the optimal concentration of 20 mg/L, apatite recovery dropped to just 10.45%, while quartz recovery remained essentially unchanged — widening the recovery gap between the two minerals to 66.9 percentage points.

In tests using an artificial mixed-mineral sample (a 1:1 mass ratio of apatite to quartz) — more closely simulating actual ore conditions — without XG-Fe3+, the resulting concentrate achieved only a 26.49% P2O5 grade with 44.21% recovery. After adding XG-Fe3+ at 100 mg/L, the P2O5 grade in the concentrate rose to its highest level of 34.48%, with a corresponding recovery of 47.61%. At a higher concentration (200 mg/L), the P2O5 grade dipped slightly to 28.47%, but recovery jumped sharply to 72.27% — showing that reagent dosage can be adjusted to balance concentrate quality against total recovery, depending on operational priorities.

Ore Samples and Industry Implications

The natural apatite and quartz samples used in the study were sourced from Guizhou Province, China — one of the country's major phosphate-bearing regions — with verified purities of 93.51% and 96.17%, respectively. The research was funded by several provincial and national science and technology programs in China, along with support from Wengfu Group — indicating this is applied research closely tied to the operational needs of a specific phosphate mining and processing company, rather than purely academic research.

For apatite mining and processing operations more broadly, this line of research carries direct practical relevance: as high-grade deposits continue to be depleted and the proportion of fine particles in mined ore keeps rising, having a specialized chemical tool to effectively handle this hard-to-process size fraction could help improve overall recovery rates across the entire processing chain — rather than accepting the loss of this valuable mineral fraction into fine tailings streams, as happens under conventional operating practices.

Source: Li, Z., Zheng, Z., He, D., Liu, G., Liu, H., Xu, W., Tang, Y., Shao, H., Shi, L. & Li, W. "Enhancing the Reverse Flotation Separation of Ultrafine Apatite and Quartz Using XG-Fe3+ as a Selective Depressant and Flocculant." Minerals 16(9), 910 (2026). DOI: 10.3390/min16090910 (open access, CC BY 4.0 license). Research conducted at Wuhan Institute of Technology, Guizhou University, and Wengfu (Group) Co., Ltd. (China).