Yijun Cao

The application of atomic force microscopy in mineral flotation

During the past years, atomic force microscopy (AFM) has matured to an indispensable tool to characterize nanomaterials in colloid and interface science. For imaging, a sharp probe mounted near to the end of a cantilever scans over the sample surface providing a high resolution three-dimensional topographic image. In addition, the AFM tip can be used as a force sensor to detect local properties like adhesion, stiffness, charge etc. After the invention of the colloidal probe technique it has also become a major method to measure surface forces. In this review, we highlight the advances in the application of AFM in the field of mineral flotation, such as mineral morphology imaging, water at mineral surface, reagent adsorption, inter-particle force, and bubble-particle interaction. In the coming years, the complementary characterization of chemical composition such as using infrared spectroscopy and Raman spectroscopy for AFM topography imaging and the synchronous measurement of the force and distance involving deformable bubble as a force sensor will further assist the fundamental understanding of flotation mechanism.

Research on Impurity Removal of Low Grade Bauxite

An acid leaching method was adopted to remove the impurities of potassium and iron from the DI (diaspore-illite) type low grade bauxite acquired from Dengfeng city of Henan province, in order to provide a higher quality raw material for the refractories industry. The effects of sulfuric acid concentration, leaching temperature, reaction time and sulfuric acid to bauxite ratio on removal efficiency of impurities were investigated. The optimum experiment conditions were: sulfuric acid concentration of 7 mol/L, reaction temperature of 90 °C, reaction time of 4 h and sulfuric acid to bauxite ratio of 6 mL/g. Under these conditions, the removal efficiency of potassium and iron were 19.2 and 94.0%, respectively. The approach presented in this work is a promising process of comprehensive utilization of low grade bauxite.

Effects of bubble size and approach velocity on bubble–particle interaction – a theoretical study

ABSTRACT A theoretical analysis of the atomic force microscopy (AFM) approach–retract dynamic interaction between an air bubble and a hydrophilic silica plane was carried out based on the well-established Stokes–Reynolds–Young–Laplace model. An air bubble with different radii attached to the end of a cantilever approached the silica surface with different approach velocities in a 10−3 M KCl solution. Results showed that with increasing approach velocity (0.1, 1, and 10 µm/s), the repulsive force, flattened area of the film, and hydrodynamic suction force between the 100-µm bubble and the silica plane increased. The film continued thinning at the initial stages of bubble retraction because of the attractive hydrodynamic pressure. When the bubble size decreased, the influence of hydrodynamic pressure was less evident. The final film thickness before bubble retraction was similar to the theoretical equilibrium thickness when the Laplace pressure was equal to the disjoining pressure. GRAPHICAL ABSTRACT

Oxidized coal flotation enhanced by adding n-octylamine

ABSTRACT Oxidized coal is difficult-to-float using conventional diesel as the collector due to the abundant oxygen-containing groups on coal surface. In this study, a short-chain cationic amine, n-octylamine, was added into diesel in 1:4 ratio for enhancing oxidized coal flotation. X-ray photoelectron spectroscopy (XPS) was used to identify the interaction mechanism between diesel-n-octylamine mixture (DO) and oxidized coal. The results showed that the flotation yield using 500 g/t DO mixture was much higher than that of using 2000 g/t diesel under a similar ash content of clean coal. The addition of n-octylamine was proven to be an effective way to lower the oily collector consumption in oxidized coal flotation. XPS showed that electrostatic bonding between n-octylamine and negative-charged hydrophilic sites on oxidized coal surface was responsible for the enhancement of flotation recovery using DO as the collector.