Effect of Dodecane and Oleic Acid on the Attachment between Oxidized Coal and Bubbles

Mengdi Xu,Yaowen Xing,Yijun Cao,Xiahui Gui

doi:10.3390/min8020029

Abstract

The objective of this study is to explain the different flotation responses observed in oxidized coal flotation when using a nonpolar flotation collector, dodecane, versus a polar flotation collector, oleic acid. Particularly, the effect of each flotation collector on bubble–coal particle attachment was investigated. Colloidal probe atomic force microscopy (AFM) was used to directly measure the force between a model coal surface and a model bubble in the presence of either dodecane or oleic acid. Pyrolytic graphite (PG) treated with oxygen plasma and a polymethylmethacrylate (PMMA) particle were selected to represent the model oxidized coal surface and model bubble. High speed visualization for bubble–oxidized coal attachment was used to monitor the attachment behavior between bubble and oxidized coal in presence of dodecane and oleic acid, respectively. It was found that the force between the oxidized PG and the PMMA particle in Milli-Q water was monotonically repulsive, illustrating that oxidized coal particles attach onto bubble surface with difficulty. The flotation recovery using a traditional hydrocarbon oil, dodecane, was always lower than when oleic acid was used at a low dosage (300–1100 g/t). The force measurements showed that an attractive hydrophobic force was introduced when a 0.01 mM oleic acid solution was used, while the force was still repulsive in presence of a 0.01 mM dodecane solution. The minimum contact time for successful attachment between oxidized coal surface and bubbles in the presence of 0.01 mM oleic acid is much shorter than that in 0.01 mM dodecane. However, a high flotation recovery of 85.81% was obtained when dodecane concentration was further increased to 1700 g/t. The significant jump into contact effect observed in the AFM force curves and the short induction time in the presence of 1 mM dodecane solution was responsible for this high flotation recovery.

Highlights

Re-utilization of oxidized coal slime waste is of practical importance for energy conservation and environment protection
We have investigated the different flotation responses of both a nonpolar flotation collector, dodecane, and a polar flotation collector, oleic acid, on oxidized coal flotation
We looked at how the presence of each flotation collector affects bubble–coal particle attachment by using a colloidal probe atomic force microscopy (AFM) technique to directly measure the force between a model coal surface (PG) and a model bubble (PMMA)

Summary

Introduction

Re-utilization of oxidized coal slime waste is of practical importance for energy conservation and environment protection. Upgrading the flotation process of oxidized coal using conventional nonpolar oily flotation collectors, such as diesel and kerosene, is difficult because of the abundance of oxygen-containing functional groups on the surface of the oxidized coal [1,2,3]. It is well known that a polar oxygen-containing flotation collector can significantly increase the oxidized coal flotation recovery [4,5,6]. Hydrogen bonding between the oxidized coal surface and the polar collector was considered to be the mechanism of flotation intensification. Gui et al [4] calculated the interfacial interaction energy between oxidized coal and two collectors, dodecane and α-furanacrylic acid, to identify the interaction mechanisms from a thermodynamic perspective. A more comprehensive understanding of how different types of collectors affect bubble–coal particle attachment is necessary

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Conclusion