The Influence of Ca2+ and pH on the Interaction between PAHs and Molybdenite Edges

He Wan,Yongjun Peng,Tingshu He,Lin Guo,Jianbo Yang,Wei Yang

doi:10.3390/min7060104

Abstract

Nonpolar hydrocarbon oils are widely used as collectors for floating molybdenite. However, they can only adsorb on molybdenite faces and not on molybdenite edges, resulting in limited molybdenite recovery, especially in processed water containing a high amounts of Ca2+. In this study, the influence of Ca2+ and pH on the adsorption of polycyclic aromatic hydrocarbons (PAHs), as part of composite collection on molybdenite edges, was studied. It was found that PAHs could only adsorb on molybdenite edges in the presence of Ca2+. Ca2+ reacted with molybdenite edges to form CaMoO4 precipitates. Then, CaMoO4 precipitates interacted with PAHs to form a structure of π–cation–π by (1) the cation–π interaction, (2) the π–π interaction and (3) the electrostatic interaction. It was also found that CaMoO4 precipitates on molybdenite edges promoted the adsorption of PAHs. The more the CaMoO4 precipitates, the easier the PAHs adsorption occurred. As a result, the high amount of Ca2+and low pH enhanced the adsorption of PAHs on molybdenite edges. This study provides insights into reducing the deleterious effect of Ca2+ on fine molybdenite flotation.

Highlights

Molybdenite is anisotropic due to its layered structure [1,2]
Some studies show that the floatability of molybdenite particles depends on the relative surface exposure of hydrophobic faces and hydrophilic edges [4,5]
The 219 nm was chosen for measuring the wavelength of polycyclic aromatic hydrocarbons (PAHs) in PAHs solutions and remaining in the solution after XLM interacted with the molybdenite sample in the subsequent study

Summary

Introduction

Molybdenite is anisotropic due to its layered structure [1,2]. It exhibits two types of surfaces, namely face and edge, resulting from the break of S–S molecular bonds (nonpolar faces) and the rupture of the strong covalent Mo–S bonds (polar edges), respectively. The face is hydrophobic, while the edge is hydrophilic. Some studies show that the floatability of molybdenite particles depends on the relative surface exposure of hydrophobic faces and hydrophilic edges [4,5]. A greater proportion of molybdenite edges corresponds to a lower flotation recovery. With the particles size decreasing, the proportion of molybdenite edges increases and molybdenite flotation recovery decreases

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