Key Takeaways & Executive Findings
- •• Penta-coordinated Cu ions on the malachite (201) and (010) surfaces exhibit stronger activity, highlighting surface anisotropy's role in sulfidation. • HS− adsorption forms more stable tetra-coordinated structures on (010) and (201) surfaces than the hexa-coordinated structure on (201), as indicated by more negative adsorption energies. • Sulfidized malachite gains an additional π electron pair and a smaller HOMO-LUMO gap with xanthate, enhancing π backbonding and collector adsorption. • The findings offer a theoretical basis for designing targeted flotation reagents that leverage coordination chemistry and Jahn-Teller effects in malachite beneficiation.
Abstract
Malachite, being highly hydrophilic and difficult to be floated conventionally, is usually beneficiated by sulfidation flotation in industry. However, the complex crystal structure of malachite leads to the formation of various fracture surfaces with distinct properties during crushing and grinding, resulting in surface anisotropy. In this study, we explored the surface anisotropy of malachite and further investigated its sulfidation mechanism from the coordination chemistry perspective, considering the influence of the Jahn-Teller effect on malachite sulfidation. Computational results reveal that the penta-coordinated Cu ions on the malachite (201) and (010) surfaces exhibit stronger activity compared to those on the malachite (201) surface. Additionally, the tetra-coordinated structure formed by HS− adsorption on the malachite (010) and (201) surfaces is more stable, with more negative adsorption energy, compared to the hexa-coordinated structure formed by HS− adsorption on the (201) surface. The sulfidized malachite surface has an additional pair of π electron and smaller HOMO (highest occupied molecular orbital)-LUMO (lowest unoccupied molecular orbital) gap with xanthate molecules, causing stronger π backbonding with xanthate. This study provides new insights into the surface sulfidation mechanism of malachite and offers a theoretical reference for the design of targeted flotation reagents.
1. Introduction
Copper, as one of the essential and important metals for industrial development, is mostly extracted from copper sulfide ores [1]. However, with the increasing demand for copper, the depletion of copper sulfide resources, and the increasingly poor, fine, and miscellaneous characteristics of copper sulfide minerals, copper oxide minerals have begun to be developed and utilized. Malachite, as one of the main copper oxide minerals, has also been widely studied. At present, forth flotation is the main method for enriching and purifying Cu in malachite, which requires that sulfur-terminated collectors have excellent interaction with the malachite surface. Nevertheless, the malachite surface has strong hydroxylation behavior [2] and high solubility [3], and the ionic bonds present on the surface can form a strong hydration layer through electrostatic interaction with water molecules, which results in unsatisfactory direct flotation effect [4]. Sulfide flotation has been proposed as a good solution to solve this problem [5, 6]. The addition of sulfidation reagents (such as Na2S, NaHS, H2S) can form a sulfide film on the malachite surface [7, 8], improving surface hydrophobicity and facilitating the subsequent adsorption of the collector xanthate.
In sulfidation-flotation system, the interaction between the sulfidation reagent and the mineral surface plays a decisive role in the effectiveness of sulfidation. It is worth noting that the structure of copper oxide minerals is complex with properties varying on different surfaces, which will have significant impact on sulfidation progress, such as nonuniform surface sulfidation. However, current research on the sulfide flot...
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Rao Xin, Zhang Chen-yang, Sun Wei, Liu Si-yuan, Yao Yu-yun, Chen Jian-hua, Zhu Yang-ge, Pei Yong, Zhang Hong-liang (2025). Malachite sulfidation flotation mechanism: Sulfidation anisotropy insights. Journal of Central South University. https://doi.org/10.1007/s11771-024-5773-6
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Frequently Asked Questions
What is the main challenge in malachite flotation?
Malachite is highly hydrophilic and has high solubility, leading to a strong hydration layer on its surface. This results in poor direct flotation. Sulfidation flotation is used to form a sulfide film that improves hydrophobicity and enables subsequent xanthate adsorption.
How does surface anisotropy affect malachite sulfidation?
Different crystal surfaces of malachite have distinct coordination environments and reactivities. The study found that penta-coordinated Cu ions on the (201) and (010) surfaces are more active, leading to nonuniform sulfidation and influencing collector adsorption.
What is the role of the Jahn-Teller effect in sulfidation?
The Jahn-Teller effect causes distortion in copper coordination geometries, which alters the stability of HS− adsorption and the electronic structure of the sulfidized surface. This ultimately affects the reactivity toward xanthate collectors.
How does sulfidation improve xanthate adsorption on malachite?
The sulfidized malachite surface has an additional pair of π electrons and a smaller HOMO-LUMO gap with xanthate, resulting in stronger π backbonding. This enhances the binding between the sulfidized surface and xanthate molecules, improving flotation efficiency.
What computational methods were used in this study?
Density functional theory (DFT) calculations were employed to explore the sulfidation mechanism from a coordination chemistry perspective, focusing on the Jahn-Teller effect and surface anisotropy.
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