Hydrophobic agglomeration behavior of rhodochrosite fines Co-induced by oleic acid and shearing

Abstract

• Agglomeration of rhodochrosite markedly depended on oleic acid concentration and pH. • Hydrophobic attraction drove agglomeration correlated with adsorption of oleic acid. • Large and dense agglomerates formed with increasing stirring rate until 500 rpm. • Excessive shearing could break agglomerates with large-scale fragmentation mechanism. • The broken fragments regrew incompletely as reducing stirring rate to initial value. Efficient separation of fine-disseminated rhodochrosite is a challenge in the purification of manganese carbonate ore and a key to reduce the discharge of electrolytic manganese slag. The agglomeration behavior of the fine particles is of importance for flotation separation. In this study, we investigated the agglomeration behavior and aggregate properties of rhodochrosite fines co-induced by oleic acid (OA) and shearing using particle size and structure analysis, surface properties measurement, extended DLVO (EDLVO) theoretical calculation and shear fracture model analysis. The results showed that rhodochrosite fines agglomerates obviously with the increasing OA concentration and pH value, and the average particle size reaches the maximum at the initial OA concentration of 1 × 10 -3 mol/L and pH of 6. The monolayer physical and chemical saturation adsorption of OA cause stronger hydrophobicity of rhodochrosite. Meanwhile, the hydrophobic attractive force between particles is stronger than electrostatic repulsive force, resulting in hydrophobic agglomeration. The moderate stirring rate is conducive to forming larger-sized and denser agglomerates with the critical rate of 500 rpm. However, intensive shearing will cause significant damage to the formed agglomerates. Besides, the volume concentrations of 10–30 μm and 30–45 μm particles increased with the increase of stirring rate after breakage and with a lower value of γ’ than 0.5, suggesting that the agglomerates breakage is mainly controlled by large-scale fragmentation mechanism. Interestingly, as recovering shearing from the higher rate to the initial rate, a secondary agglomeration is achieved by the regrowth of core (30–45 μm particles) and attach of branches and coatings (some < 10 μm and 10–30 μm particles) under the synergy of hydrophobic attraction and shearing. However, it did not fully recover back to the original balanced state before fragmentation, which was due to irreversible damage caused by excessive shearing. This research will be beneficial for in-depth understanding of agglomeration mechanisms of rhodochrosite fines and provide a basis for subsequent efficient flotation separation.