Contribution of friction to the heterocoagulation between coal surface and quartz particles studied by the particle vision and measurement (PVM)

Abstract The heterocoagulation between coal and micron-sized gangue particles is detrimental to the flotation separation of clean coal. Mineral heterocoagulation is usually inhibited by the adjustment of solution chemistry. But it is not explicit whether solution chemistry adjustment is universally suitable to inhibit heterocoagulation of gangue particles of different sizes, as the heterocoagulation mechanism may vary with the increase of particle size. In this work, the heterocoagulation between coal surface and quartz particles of different particle size was observed in turbulent flow field at acid and neutral pH by the in-situ particle vision and measurement (PVM) probe and was quantified via image processing. The observations indicated that the heterocoagulation between coal surface and fine quartz particles (D3,2 = 11 and 21 µm) was mitigated as pH varied from 3 to 7, however, the heterocoagulation between coal surface and coarse quartz particles (D3,2 = 31 µm) unexpectedly did not change with pH. The dependence of heterocoagulation on pH was different for fine and coarse quartz particles, indicating the variation of heterocoagulation mechanism. The heterocoagulation of fine quartz particles was regulated by the electrostatic double layer force in the framework of the DLVO theory, whereas the heterocoagulation of coarse quartz particles was mainly attributed to the non-DLVO force such as friction.