Key Takeaways & Executive Findings
- •• Alkaline pH enhances APAM adsorption on hematite, increasing from 0.106 to 0.186 mg/m2, due to surface deprotonation and stronger Fe–OOC coordination. • Alkaline conditions promote the formation of larger and denser flocs, with size increasing from 56 to 982 μm and fractal dimension from 1.44 to 1.87. • Improved floc structure leads to significantly better sedimentation, reducing turbidity from 436.8 to 76.7 NTU and increasing settled solids from 35.94% to 52.43%. • A multi-scale correlation model quantitatively links interfacial chemistry, floc structural evolution, and settling behaviour, providing a unified mechanistic basis for pH-regulated hematite flocculation.
Abstract
Efficient flocculation and sedimentation of ultrafine hematite remain a key challenge in mineral processing. This study elucidates the pH-dependent flocculation behaviour of hematite with anionic polyacrylamide (APAM) using a multi-scale correlation framework integrating interfacial analysis, structural characterization, and sedimentation evaluation. Increasing pH induces progressive surface deprotonation, yielding a more negative hematite surface and enhanced APAM adsorption from 0.106 to 0.186 mg/m2. FTIR, XPS, and molecular dynamics simulations consistently reveal strengthened Fe–OOC coordination, intensified hydrogen bonding, and more stabilised polymer conformations under alkaline conditions. Microscopy, SEM, and FBRM show that alkaline conditions facilitate the formation of larger and denser flocs, with size increasing from 56 to 982 μm and fractal dimension from 1.44 to 1.87. These structural changes markedly improve sedimentation performance, reducing turbidity from 436.8 to 76.7 NTU and increasing settled solids from 35.94 to 52.43 percent. The proposed multi-scale correlation model quantitatively links interfacial chemistry, floc structural evolution, and settling behaviour, providing a unified mechanistic basis for pH-regulated hematite flocculation. This framework not only advances understanding of polymer–mineral interactions but also offers practical guidance for optimising solid–liquid separation and tailings-water recycling in fine mineral beneficiation.
1. Introduction
Hematite is one of the most important iron ore resources for the steel industry [1–3]. Due to increasingly fine grinding in regions such as Anshan and Benxi, ultra-fine particles (<30 μm) can account for over 90% of the concentrate. These particles settle poorly in thickening operations, leading to high overflow solids, sludge accumulation in recycled water, and instability in downstream flotation [4,5]. Such issues reduce beneficiation efficiency and increase the burden on tailings dams, highlighting the urgent need for more effective flocculation and sedimentation technologies [6–8].
Anionic polyacrylamide (APAM) is widely used in fine mineral slurries for its strong bridging capability and high flocculation efficiency [4,9–11]. For hematite, the surface properties of ultra-fine particles are strongly controlled by slurry pH, which regulates the protonation state of surface hydroxyl groups [12–14], modifies surface charge and zeta potential, and governs the dissociation and conformation of APAM carboxyl groups [15,16]. Hematite typically exhibits an isoelectric point of pH 3–6 [17–19], making pH a key factor in determining electrostatic interactions and polymer adsorption. Although numerous studies have examined pH effects, most have focused on single indicators such as zeta potential, adsorption amount, or settling performance, leaving the molecular mechanisms that connect interfacial electrochemistry to floc formation insufficiently resolved [20,21].
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ZHANG Ke Kang, SHEN Yanbai, CUI Baoyu, GAO Shuling, LIU Wengang, ZHAO Qiang (2026). Unravelling the pH-driven multiscale cascade of hematite flocculation: From interfacial tuning to structural assembly and sedimentation dynamics. SinoTechIntel Verified Research. https://doi.org/10.1016/j.ijmst.2026.02.003
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Frequently Asked Questions
How does pH affect the flocculation of hematite with anionic polyacrylamide?
Increasing pH enhances APAM adsorption on hematite surfaces due to surface deprotonation, leading to stronger Fe–OOC coordination and hydrogen bonding. This results in larger and denser flocs, improving sedimentation performance.
What are the key findings of the study on hematite flocculation?
The study reveals that alkaline conditions increase APAM adsorption from 0.106 to 0.186 mg/m2, floc size from 56 to 982 μm, and fractal dimension from 1.44 to 1.87, while reducing turbidity from 436.8 to 76.7 NTU and increasing settled solids from 35.94% to 52.43%.
What is the significance of the multi-scale correlation model proposed in the paper?
The model quantitatively links interfacial chemistry, floc structural evolution, and settling behaviour, providing a unified mechanistic basis for pH-regulated hematite flocculation. It offers practical guidance for optimizing solid–liquid separation and tailings-water recycling.
What methods were used to characterize the flocculation process?
The study employed FTIR, XPS, molecular dynamics simulations, microscopy, SEM, and FBRM to analyze interfacial interactions, polymer conformations, and floc structure.
Why is efficient flocculation of ultrafine hematite important?
Ultrafine hematite particles settle poorly, causing high overflow solids, sludge accumulation, and instability in downstream processes. Efficient flocculation improves solid–liquid separation, reduces environmental burden, and enhances beneficiation efficiency.
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