Key Takeaways & Executive Findings
- •• Identified sequential intermediate products (green rust, feroxyhyte, weakly crystalline nanoparticles) during magnetite crystallization, revealing a dissolution-recrystallization transformation mechanism. • Demonstrated that zinc binds strongly to green rust via adsorption and lattice substitution, explaining the difficulty in separating zinc from magnetite. • First-time elucidation of zinc binding configurations with key intermediate products, providing mechanistic insights for optimizing iron and zinc separation. • Offers a novel approach for iron removal and resource recycling in zinc hydrometallurgy, potentially reducing hazardous waste and environmental impact.
Abstract
Iron removal from zinc leachate in hydrometallurgy produces large volumes of low-grade, impurity-laden iron waste, posing significant environmental challenges. Magnetite precipitation offers a novel method for iron removal and resource recycling in zinc hydrometallurgy. However, the chemical similarity between ferrous and zinc ions, along with high zinc concentrations, causes zinc co-precipitation, challenging its application. To address this issue, this study utilized electron microscopy to observe key intermediate products in magnetite crystallization and employed EXAFS (extended X-ray absorption fine structure) to analyze their evolutionary mechanisms and zinc-binding configurations. The results indicate that the intermediate products during magnetite formation are sequentially green rust, feroxyhyte (δ-FeOOH), and weakly crystalline nanoparticles, and further analysis revealed that their transformation follows the dissolution-recrystallization mechanism. Furthermore, it was found that intermediate products such as green rust exhibit strong binding with zinc (via adsorption and lattice substitution), which was confirmed as a significant reason for the difficulty in separating zinc from magnetite. This study elucidates the transformation process of intermediate products during magnetite formation and, for the first time, reveals the binding configurations of zinc with these key intermediate products. This has significant implications for the development and optimization of new technologies for the efficient separation of iron and zinc during the magnetite precipitation process.
1. Introduction
More than 85% of the global zinc production originates from a process involving roasting, leaching, and electrolysis [1−3]. In this process, zinc concentrates (ZnS) are first roasted to produce zinc calcine (ZnO). The zinc calcine is then subjected to neutral leaching to extract zinc into solution, while the remaining zinc residue undergoes hot acid leaching. However, zinc concentrates often contain significant amounts of iron, which dissolves into the leach solution during hot acid leaching. Since iron impurities can interfere with the subsequent zinc electrolysis process, it is essential to remove iron from the hot acid leachate. Currently, common iron removal methods include jarosite precipitation, goethite precipitation, and hematite precipitation. However, the iron precipitation process generates substantial low-iron hazardous waste [4, 5]. In China, millions of tons of iron-bearing residues from zinc hydrometallurgy accumulate each year, with the volume increasing by over 100000 t annually [6 −8]. These residues cannot be directly used as raw materials for ironmaking, necessitating long-term storage and disposal, which poses serious environmental and resource management challenges [9 −11]. Moreover, iron-bearing residues typically contain toxic metals like lead, arsenic, and chromium, which can leach into soil and groundwater over time, further exacerbating environmental risks [12, 13]. Given these challenges, there is a growing need for alternative iron removal methods that can both effectively address iron contamination and minimize waste generation.
Magnetite precipitation represents a novel and promising approach to iron removal. Compared with traditional sources of iron-rich precipitates, magnetite is the iron oxide with the highest iron content, theoretically reaching up to 72.4%, making it an ideal raw material for iron smelting [14, 15]. Moreover, the formation of magnetite requires relatively mild conditions, as it does not necessitate high temperatures or pressures, and the reaction time is comparatively short. Its strong magnetic properties also facilitate easy separation from the solution, offering a potential advantage over conventional methods. However, the presence of high zinc concentrations in the leachate can lead to zinc co-precipitation, which challenges the efficiency of the process. This study aims to understand the transformation pathways and zinc binding mechanisms during magnetite crystallization, providing insights for optimizing iron and zinc separation in zinc hydrometallurgy.
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LI Chun-xue, WU Jia-hui, ZHANG Wen-chao, SHI Mei-qing, WANG Yun-yan, DUAN Ying, YAN Xu, WANG Qing-wei, MIN Xiao-bo, CHAI Li-yuan (2025). Transformation pathways and zinc binding mechanisms in magnetite crystallization: Implications for zinc hydrometallurgy. Journal of Central South University. https://doi.org/10.1007/s11771-025-6106-0
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Frequently Asked Questions
What is the main challenge in using magnetite precipitation for iron removal in zinc hydrometallurgy?
The main challenge is the co-precipitation of zinc with iron due to the chemical similarity between ferrous and zinc ions and high zinc concentrations, which complicates the separation of iron and zinc.
What intermediate products were identified during magnetite crystallization?
The intermediate products were identified as green rust, feroxyhyte (δ-FeOOH), and weakly crystalline nanoparticles, which transform sequentially via a dissolution-recrystallization mechanism.
How does zinc bind to the intermediate products?
Zinc binds to intermediate products such as green rust through adsorption and lattice substitution, which was confirmed as a significant reason for the difficulty in separating zinc from magnetite.
What is the significance of this study for zinc hydrometallurgy?
This study provides mechanistic insights into the transformation pathways and zinc binding configurations, which can guide the development of new technologies for efficient iron and zinc separation, reducing hazardous waste and improving resource recycling.
What methods were used to analyze the intermediate products?
The study utilized electron microscopy to observe key intermediate products and EXAFS (extended X-ray absorption fine structure) to analyze their evolutionary mechanisms and zinc-binding configurations.
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