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Effect of surface relaxation of rhodochrosite (104) and substitution of Mn by Ca on the electronic structure of rhodochrosite

Zhang Jingqi, Zhang Qin, Zhang Tiebin

Physicochemical Problems of Mineral Processing

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2022

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Vol. 58, iss. 3

art. no. 145991

EN

To explore the difference between the surface and crystal structure of rhodochrosite, relaxation and reconstruction of the rhodochrosite (104) surface are studied by using Density Functional Theory. The calculation results indicated that the C and O atoms with lower reactivity tend to be enriched on the surface, while the Mn atoms with the highest reactivity moved away from the surface. The band gap width decreased from 1.814 eV to 1.614 eV after the formation of the rhodochrosite (104) surface. The electrons on the rhodochrosite (104) surface are more active than crystal. Ca substitution makes the atomic activity on the (104) surface of rhodochrosite more stable. Ca substitution reduces the ability of the surface of rhodochrosite to absorb external electrons, and the surface electrical properties decrease.

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First-principles calculations of electronic structure of rhodochrosite with impurity

He Guichun, Li Kun, Li Kun, Guo Tengbo, Li Shaoping, Huang Chaojun, Zeng Qinghua

Physicochemical Problems of Mineral Processing

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2020

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Vol. 56, iss. 1

195--203

EN

The electronic structure of rhodochrosite containing impurity defects is studied by using the first principles density functional theory. The energy band structure, density of states and electronic distribution are calculated for rhodochrosite crystal models with various impurities (e.g., Cu, Ca, Mg, Zn, Fe). This paper discusses the effects of such defects on the electronic structure of rhodochrosite. The calculation results show that the impurity defects have a great impact on the surface electrical properties of rhodochrosite. For example, Ca and Mg impurities reduce the semiconductor width of rhodochrosite. Both Ca and Mg atoms in orbital bonding act as electron donors in which Ca3p and Mg2p orbits provide electrons while O2p orbits receive electrons. Moreover, the more number of valence electrons of Mn is the weaker covalent interaction between Mn and O atoms will be. Meanwhile, decrease of the total energy of rhodochrosite, makes the structure more stable. When Fe, Zn and Cu impurities are contained, the forbidden gap becomes narrower, which improves the conductivity of rhodochrosite. In addition, impurity bands will be formed in the 3d orbits of rhodochrosite as shown in its density of states, and the number of electrons in 3d orbits will increase. This weakens the covalence of O atoms, decreases the population values of O-Mn, increases the bond length, and enhances the ionicity of O-Mn bonds. The impurity of all defects considered in this study have shown an improved conductivity of rhodochrosite, and increased hole concentration of Mn atoms, which will be of great benefit to the adsorption of anionic collectors and enhance the electrochemical properties for rhodochrosite flotation process.

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Study on a novel hydroxamic acid as the collector of rhodochrosite

Zhao G., Dai T., Wang S., Zhong H.

Physicochemical Problems of Mineral Processing

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2018

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Vol. 54, iss. 2

428--439

EN

A novel collector, tert-butyl benzohydroxamic acid (TBHA), was first introduced in rhodochrosite flotation. The performance of TBHA was investigated by the density functional theory (DFT) calculation along with the micro flotation test, zeta potential determination and XPS analysis, compared with benzohydroxamic acid (BHA). TBHA has stronger affinity to the mineral than BHA in terms of frontier molecular orbital, atomic net charge and bond population. The substitution of tert-butyl group on the benzene ring improves the affinity of the hydroxamic acid to the mineral. TBHA exhibits excellent collecting ability to rhodochrosite with a recovery of about 99% at a concentration of 3.89×10-4 mol/dm3 and pH 6.5. The hydroxamic acid molecules are adhered on mineral surfaces by chemical adsorption, resulting in negative shifts for the zeta potential of rhodochrosite with the presence of the collector. Chemical adsorption can be also confirmed from XPS analyses that the atomic concentration ratios of C and O to Mn on the treated mineral surfaces were increased and the binding energy of Mn3s was decreased. The experimental data achieve excellent agreement with the computational analyses.