Entrainment In Flotation Research Articles

Purification of graphite from spent carbon cathodes through the reduction of the mechanical entrainment of cryolite using polyaluminium chloride as a flocculant

Spent carbon cathodes (SCCs) generated during electrolytic aluminum production pose significant environmental hazards. To optimize resource utilization, flotation is used as an early process for the clean recovery of valuable graphite from waste cathodes. However, the mechanical entrainment in flotation restricts the further improvement of product purity, resulting in an increase in waste gas and wastewater discharge in the subsequent purification process. In this study, to increase the fixed carbon content of flotation products, flocculant was first applied to the flotation separation of SCCs, and polyaluminum chloride (PAC) was used to flocculate cryolite with high impurity content to reduce mechanical entrainment in the flotation process. Zeta potential measurements, particle size analysis, optical microscopy, and scanning electron microscopy confirmed the agglomeration of cryolite under the action of PAC. Additionally, the DLVO (Derjaguin, Landau, Verwey, and Overbeek) theory was used to estimate the interaction energy to further explain the mechanism underlying cryolite agglomeration. Interaction energy calculation revealed that the attraction energy between particles was dominant at the PAC concentration of 2000 mg/L. Flotation experiments indicated that under a constant pulp pH of 7.8, the absence of sodium silicate, and a stirring speed of 1200 rpm, mechanical entrainment decreased from 91.53 ± 1.53 g/L to 69.80 ± 1.90 g/L, and the carbon grade of the product increased from 83.07 ± 0.28% to 88.94 ± 0.30%. Overall, the proposed purification method provides a new approach for the efficient recovery of graphite in waste cathodes, which is of great significance for the sustainable development of graphite resources.

Foaming and aggregation behaviours of polyethylene oxide and polyacrylamide in inhibiting mechanical entrainment of kaolinite in flotation using saline water

The recovery of fine gangue particles by mechanical entrainment through the liquid between air bubbles in flotation is a major challenge in resource processing. This study explored high molecular weight polyacrylamide copolymer Magnafloc 1011 (MF1011) and polyethylene oxide (PEO), two widely used flocculants, in inhibiting mechanical entrainment of kaolinite in flotation using saline water. It was found that anionic MF1011 effectively inhibited kaolinite entrainment, but non-ionic PEO did not. The measurement of in-situ particle sizes, network structures of kaolinite and the foamability of polymer solutions indicated that the inhibition of kaolinite entrainment in flotation was governed by the network structures induced by the polymer and the polymer’s foamability. MF1011 produced a compact network structure which facilitated the drainage of kaolinite from the liquid between air bubbles and therefore the inhibition of kaolinite entrainment. By contrast, PEO produced a sponge-like network structure with a larger size which retained more water and slowed down the drainage of kaolinite. In addition, PEO was surface-active and increased the foam stability with a thicker film of liquid between air bubbles to carry kaolinite, further slowing down the drainage of kaolinite. This study demonstrates that the reduction of mechanical entrainment in flotation by flocculants is not only related to the size enlargement but also highly dependent on the aggregation structure and the flocculants’ foamability. The findings from this work will provide important guidance to select flocculants to minimize fine gangue entrainment in flotation.

An empirical model for the degree of entrainment in froth flotation based on particle size and density

The degree of entrainment is significantly influenced by particle size and density but there is no consensus in the literature, however, on the mechanisms involved. In addition, there has been a lack of rigorous experimental validation of proposed theories. In this study, entrainment tests with only gangue minerals were performed in a 3.5L laboratory mechanical flotation cell using fully liberated quartz, ilmenite and hematite. The results suggest that the drainage of solids relative to water in the froth (i.e. the degree of entrainment) is a consequence of the balance between the drag force on the particle, and the apparent immersed weight of the particle in the water which potentially changes the particle settling rate. Particle size and density are two variables that affect drag force and apparent immersed weight. Therefore, particles with different particle size and density have different particle settling rates relative to water, and thus exhibit different degrees of entrainment in flotation. A new empirical model for the degree of entrainment was then proposed, incorporating the mechanism underpinning the effect of particle size and density. Results indicate that the model can be employed to predict the degree of entrainment of different gangue minerals on a size-by-size basis.

The effect of biopolymer dispersants on copper flotation in the presence of kaolinite

In this study, three lignosulfonate-based biopolymers, DP1775, DP1777 and DP1778 with different compositions were examined as dispersants in copper flotation in the presence of kaolinite. While rheological measurements indicated that these biopolymers dispersed the kaolinite aggregates, flotation results revealed that the three biopolymers increased the copper recovery, with a decline in copper grade, which was attributed to an interaction of biopolymers with the frother modifying the froth and enhancing the mechanical entrainment. Two-phase foam characterisation revealed a larger height in the blends of biopolymer and frother, which in turn promoted the mechanical entrainment in flotation. The dispersing and foaming abilities of biopolymers were governed by their structural features such as the content of functional groups, the molecular weight and counterions. This study indicates that when selecting a polymeric dispersant in flotation to deal with clay minerals, its froth property should also be taken into consideration.

Flocculation of Pyrite Fines in Aqueous Suspensions with Corn Starch to Eliminate Mechanical Entrainment in Flotation

The hydrophilic flocculation of pyrite fines in aqueous suspensions with corn starch was studied by measuring particle size distribution, microscopy observation and micro-flotation. Furthermore, the interaction of corn starch with pyrite was investigated by determining the adsorption density and based on zeta potential measurements and X-ray photoelectron spectrometer (XPS) analysis in this work. The results of the particle size distribution measurement show that corn starch can effectively aggregate pyrite fines, and the pyrite floccules (flocs) are sensitive to mechanical stirring. The micro-flotation results suggest that the mechanical entrainment of pyrite fines in flotation can be effectively eliminated through the formation of large-size flocs. The zeta potential of pyrite particles decreases with the addition of corn starch. The XPS results prove that carboxyl groups are generated on the digested corn starch, and both iron hydroxyl compounds and ferrous disulfide on the pyrite surface can chemically interact with the corn starch digested by sodium hydroxide.

The effect of hydrodynamic conditions on true flotation and entrainment in flotation of a complex sulphide ore

The separation efficiency and selectivity of flotation are directly proportional to recoveries of the mineral species in the feed due to true flotation and entrainment. In this study, effects of the hydrodynamic conditions on true flotation and entrainment were investigated by using a fractional factorial experimental design. A method previously described in the literature was applied to determine the contributions of true flotation and entrainment in flotation of a complex sulphide ore. In order to apply the method, the kinetic flotation tests were conducted under various hydrodynamic conditions defined by some physical variables. Some of these tests were conducted in the presence and absence of a collector to evaluate the self-induced floatability. The selectivity index of the mineral species for entrainment was seen to be suitable evaluation of the non-selectivity and efficiency of the entrainment. Furthermore, the results of the size-by-size analysis of the froth products indicated that the presence of the self-induced hydrophobic particles in the feed is as important as the presence of very fine particles for accurate estimation of true flotation and entrainment in flotation of a complex sulphide ore. In addition, the estimated results for entrainment in flotation of the complex sulphide ore can be misleading. Therefore, a new approach would be necessary to determine the contributions of true flotation and entrainment in flotation of a complex sulphide ore.

Modelling of entrainment in industrial flotation cells: Water recovery and degree of entrainment

Entrainment in flotation can be considered as a two-step process, including the transfer of the suspended solids in the top of the pulp region just below the pulp–froth interface to the froth phase and the transfer of the entrained particles in the froth phase to the concentrate. Both steps have a strong classification characteristic. The degree of entrainment describes the classification effect of the drainage process in the froth phase. This paper briefly reviews two existing models of degree of entrainment. Experimental data were collected from an Outokumpu 3 m 3 tank cell in the Xstrata Mt. Isa Mines copper concentrator. The data are fitted to the models and the effect of cell operating conditions including air rate and froth height on the degree of entrainment is examined on a size-by-size basis. It is found that there is a strong correlation between the entrainment and the water recovery, which is close to linear for the fines. The degree of entrainment decreases with increase in particle size. Within the normal range of cell operating conditions, few particles coarser than 50 μm are recovered by entrainment. In general, the degree of entrainment increases with increase in the air rate and decreases with increase in the froth height. Air rate and froth height strongly interact with each other and affect the entrainment process mainly via changes in the froth retention time, the froth structure and froth properties. As a result, other mechanisms such as entrapment may become important in recovering the coarse entrained particles.

A simple model for the calculation of entrainment in flotation

Theoretical and experimental studies have been performed to analyze the entrainment of both hydrophilic and hydrophobic particles in flotation. A new model is proposed for the entrainment based on the water recovery trend. Two sets of timed flotation experiments were carried out to validate the model. These experiments were realized with quartz and pyrite as the only mineral in the pulp and with various frother concentrations and pulp densities. The chemical conditions of the pulp were adjusted to float pyrite as hydrophobic and to depress quartz as hydrophilic mineral. The solids recovery for each size fraction and water recovery was measured in these experiments. The proposed empirical model equation was checked against experimental observations. It was observed that the model equation well represented the entrainment-water relationship. Since hydrophilic mineral recovery mainly depends on the entrainment, the data obtained from quartz only tests were first fitted to the entrainment equation. The fit for quartz data was found to be satisfactory. This shows that the proposed model could be used to define the behavior of hydrophilic particles in a batch flotation test. The same model was applied for pyrite only tests and contribution of entrainment to hydrophobic mineral recovery was calculated. The results provided accurate interpretation of hydrophobic mineral entrainment, which is difficult to directly measure.

Investigation of coal and ash recovery and entrainment in flotation

This paper discusses the effect of particle size, impeller speed and pulp density on flotation and entrainment of coal and associated gangue, consisting mostly of kaolinite and illite. Experimental work indicated that particle size was the most important parameter influencing the recovery and entrainment behavior of coal and ash. The effects of impeller speed and pulp density were found to be less on entrainment. Lower agitation or solid density with higher kerosene concentrations yielded more selective froth products at the same recovery level and lower entrainment.