Manipulating the interaction forces between an air bubble and oil is of great importance in many industrial processes, such as oil sands extraction. Recently, sodium citrate has been applied in the alkaline hot-water extraction process to improve the recovery of bitumen from mined oil sands. In this study, bubble probe atomic force microscopy was used to directly investigate the effect of Na3Cit on the interaction force between an air bubble and a bitumen surface in different water chemistry. The experimental forces were compared with the Stokes–Reynolds–Young–Laplace film drainage model considering contributions from surface forces, and the theoretical calculation indicated that competition between the electrostatic double layer (EDL) force and the hydrophobic force determined the bubble–bitumen attachment. In pure electrolyte solution at pH 8.5, it was observed that the ionic strength required to induce bubble–bitumen attachment followed CaCl2 < NaCl < Na3Cit. The zeta potentials of both the air bubble and bitumen surfaces increased in magnitude in the same order, indicating that the stability in sodium citrate was caused by EDL repulsion. In the presence of CaCl2, the addition of Na3Cit changed both bitumen zeta potential and Debye length, modulating the EDL interaction and affecting bubble–bitumen attachment behavior. By performing a series of experiments containing both CaCl2 and Na3Cit, a stability map was produced. Compared to sodium citrate alone, the copresence of CaCl2 and Na3Cit facilitated bubble–bitumen attachment. Once the CaCl2 concentration exceeded 5 mM, bubble–bitumen attachment always happened, regardless of the Na3Cit concentration. The findings provide insight on how Na3Cit, in combination with CaCl2, affects bubble–bitumen attachment and offer valuable information on controlling the interaction force between the air bubble and bitumen by adjusting the water chemistry.

For the purpose of understanding the colloidal behaviors of illite in mineral processing, probing the surface charging property of illite is of great significance. This research explored the edge and basal surfaces of illite using an atomic force microscope (AFM). The interaction forces between Si/ Si 3 N 4 probes and illite edge/basal surfaces were measured, respectively, at different pH values in 10 mM KCl solutions. Theoretical Derjaguin−Landau−Verwey−Overbeek forces were matched up with the measured forces to derive the surface potentials of the two surfaces. On the illite basal surface, an attractive force occurred at pH 3.0, while repulsive forces dominated from pH 5.0 to 10.0. On the illite edge surface, a slight attractive force was also obtained at pH 3.0. However, the interaction changed into repulsion at pH 5.0, and this repulsive force increased gradually from pH 6.0 to 10.0. Illite basal and edge surfaces were both negatively charged, but the basal surface exhibited more negative charges than the edge surface from pH 3.0 to 10.0. Increasing solution pH from 3.0 to 10.0, there was no detection of the point of zero charge (PZC) of the illite basal surface; however, the PZC of the illite edge surface should have occurred at a pH slightly lower than 3.0. This is the first time that surface potentials of illite edge and basal surfaces were attained separately by direct force measurements. These findings provide insights into the colloidal behaviors of illite in mineral processing and oil sands extraction.

Molybdenite (MoS 2 ) is a mineral that has drawn great interest because of its potential application in various fields. To facilitate the flotation of molybdenite, the mineral pulp is commonly treated with nonpolar oil additives to promote hydrophobicity and to form an oil bridge between ultrafine molybdenite particles for agglomeration. In this study, dodecane was chosen as a model oil to investigate the flotation mechanisms of molybdenite with nonpolar oil. The interaction forces between a micrometer-sized dodecane droplet and the molybdenite basal plane in various electrolyte solutions were directly measured by the atomic force microscope droplet probe technique. The effects of added salts, ionic strength, and solution pH on interaction forces were evaluated by considering van der Waals, electrical double-layer (EDL), and hydrophobic forces. The experimentally measured force curves were found to agree well with the Reynolds lubrication model and the augmented Young−Laplace equation. The results show that the competition between repulsive EDL forces and attractive hydrophobic forces was directly responsible for oil−molybdenite attachment behavior. High pH and low salinity (<24 mM NaCl) led to strong repulsive EDL forces, which stabilized the interaction and prevented the attachment of oil to molybdenite. Both low pH and high salinity facilitated the attachment of oil to molybdenite through the depression of EDL force, allowing attractive hydrophobic force to dominate. The hydrophobic attraction was quantified with an exponential decay length of 1.0 ± 0.1 nm. Furthermore, calcium ions decreased the magnitude of the surface potentials of both oil and molybdenite more than that seen with the same ionic strength of sodium ions, suggesting the suppressed EDL repulsion. This study provides quantitative information about the surface forces between oil and the molybdenite basal plane and an improved understanding of the fundamental interaction mechanisms governing molybdenite recovery by mineral flotation.

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Biomonitoring at contaminated sites undergoing cleanup, including Superfund sites, often uses bioaccumulation of anthropogenic contaminants by field-deployed organisms as a metric of remedial effectiveness. Bioaccumulation studies are unable to assess the equilibrium status of the organisms relative to the contaminants to which they are exposed. Establishing equilibrium provides a reproducible benchmark on which scientific and management decisions can be based (e.g., comparison with human dietary consumption criteria). Unlike bioaccumulating organisms, passive samplers can be assessed for their equilibrium status. In our study, over a 3-year period, we compared the bioaccumulation of selected polychlorinated biphenyls (PCBs) by mussels in water column deployments at the New Bedford Harbor Superfund site (New Bedford, MA, USA) to codeployed passive samplers. Based on comparisons to the calculated passive sampler equilibrium concentrations, the mussels were not at equilibrium, and the subsequent analysis focused on evaluating approaches for estimating equilibrium bioaccumulation. In addition, a limited evaluation of metal bioaccumulation by the exposed mussels and a metal passive sampler was performed. In general, mussel and passive sampler accumulation of PCBs was significantly correlated; however, surprisingly, agreement on the magnitude of accumulation was optimal when bioaccumulation and passive sampler uptake were not corrected for nonequilibrium conditions. A subsequent comparison of four approaches for estimating equilibrium mussel bioaccumulation using octanol-water partition coefficients (K OW ), triolein-water partition coefficients (K TW ), and two types of polymer-lipid partition coefficients demonstrated that field-deployed mussels were not at equilibrium with many PCBs. A range of estimated equilibrium mussel bioaccumulation concentrations were calculated, with the magnitude of the K OW -based values being the smallest and the polymer-lipid partition coefficient-based values being the largest. These analyses are intended to assist environmental scientists and managers to interpret field deployment data when transitioning from biomonitoring to passive sampling.