Application of Depletion Attraction in Mineral Flotation: II. Effects of Depletant Concentration

Abstract

Along with the accompanying theory article, we experimentally investigate the effect of the depletion attraction force on the flotation of malachite. While varying the concentration of the depletion agent (polyethylene glycol), three different systems are studied: pure malachite, pure silica and a 1:1 mass ratio of malachite and silica binary system. We find that the recovery increases significantly as the concentration of the depletion reagents increases for all three systems. However, the recovery suddenly decreases in a certain concentration range, which corresponds to the onset of the decreased surface tension when high concentrations of the depletion agent are used. The decreased surface tension of the air/water interface suggests that the recovery rate is lowered due to the adsorption of the depletion agent to the bubble surface, acting as a polymer brush. We also perform experiments in the presence of a small amount of a collector, sodium oleate. An extremely small amount of the collector (10−10–10−5 M) leads to the increase in the overall recovery, which eventually reaches nearly 100 percent. Nevertheless, the grade worsens as the depletant provides the force to silica particles as well as target malachite particles.

Application of Depletion Attraction in Mineral Flotation: I. Theory

“…The DLVO interaction parameters are the same as those in Figure 2a. It is clearly seen that E B decreases significantly with increases in the concentration of the depletion agent, which is also proven by our experimental results [70]. Therefore, this result strongly indicates that particle attachment could become far easier in the presence of depletion agents.…”

“…Once adsorbed, those depletants at the surface function as polymer brushes rather than depletion agents [43][44][45]74]. Here, the depletion agent is assumed to be PEG because it is used in the companion experimental paper [70]. Assuming that PEG is reversibly adsorbed onto the bubble surface, which is an appropriate assumption for a soluble surfactant (i.e., Gibbs monolayer) [75], the surface concentration of the polymer depends on the bulk concentration of PEG in equilibrium, although most PEG molecules remain in the bulk [75,76].…”

“…Assuming that PEG is reversibly adsorbed onto the bubble surface, which is an appropriate assumption for a soluble surfactant (i.e., Gibbs monolayer) [75], the surface concentration of the polymer depends on the bulk concentration of PEG in equilibrium, although most PEG molecules remain in the bulk [75,76]. Because the depletion attraction and polymer brushes compete as their concentrations increase, an optimum concentration of depletion agent exists [70]. In general, a high concentration of depletant provides a higher attraction.…”

Monolithic Chiral Nematic Organization of Cellulose Nanocrystals under Capillary Confinement

“…We suggest that helix axis alignment is due to the competition between capillary flow, boundary layer condition, and Marangoni flow at the receding front. − Upon drying, the CNC/TOPA/PEG LC suspension at the surface continuously flows outward from the center to the liquid/air/capillary wall interface due to the capillary force . The CNC/TOPA/PEG concentration is higher at the edge region, which reduces the surface tension due to the lower surface tension of the PEG and CNC suspension and generates an inward flow toward the tube center known as the Marangoni flow …”

“…58−60 Upon drying, the CNC/TOPA/ PEG LC suspension at the surface continuously flows outward from the center to the liquid/air/capillary wall interface due to the capillary force. 58 The CNC/TOPA/PEG concentration is higher at the edge region, which reduces the surface tension due to the lower surface tension of the PEG 61 and CNC suspension 58 and generates an inward flow toward the tube center known as the Marangoni flow. 59 The chiral nematic phase alignment is controlled by the balance between the static boundary layer at the wall surface and Marangoni flow, giving rise to a transitional region with conflicting orientations of helical axes (Figure 6c).…”