Shear Flocculation Research Articles

Impact of power input in pulp conditioning on coal flotation and real-time characterization by focused beam reflectance measurement (FBRM)

ABSTRACT Pulp conditioning is a necessary procedure in the coal flotation industry, and optimizing the power input of such processes is in favor of improving flotation efficiency and reducing costs. This paper applied a pulp conditioning system combined with the focused beam reflectance measurement (FBRM) to investigate the impact of power input on coal flotation. Under the same energy input, the highest flotation efficiency of 50.09% was achieved in a pulp conditioning pattern of 1800 rpm-3 min, but the flotation efficiency reached only 36.13% in 1200 rpm-7.2 min. The kerosene collector can disperse into large numbers of droplets that exceed 2000 counts/s at size fractions of −10 μm and 20–50 μm in high power input and achieve better adsorption on coal. In the pulp conditioning process, the coal particle numbers of −50 μm size fraction decreased significantly from 15,000 counts/s to nearly 8000 counts/s at 32.3 W power input and coarse aggregates of 50–1000 μm size were detected. Under high power input conditions caused by high agitation speed, extra energy contributed validly to the kinetic energy of coal particles/collector droplets and the generation of oil-water and oil–coal interfaces. The shear flocculation behavior induced by the high power inputs in pulp conditioning is favorable for the flotation recovery of fine and ultra-fine particles.

Enhancement of shear flocculation of a galena suspension by ultrasonic treatment

The enhancement of shear flocculation of a galena suspension by ultrasound in the presence of sodium isopropyl xanthate and potassium ethyl xanthate was investigated by studying the effects of surfactant concentration on flocculation efficiency, contact angle, and zeta potential. Strong flocculation was obtained under alkaline conditions (pH > 9) and a high ultrasound power level (150 W). Although the ultrasonic treatment increased the negativity of the zeta potential of the galena particles, this did not decrease the flocculation efficiency, thereby showing that the hydrophobic interactions between the particle were stronger than the electrical double-layer repulsion resulting from xanthate adsorption. The findings indicate that the ultrasonic treatment promoted the adsorption of surfactants onto the mineral surfaces.

Quartz Fine Particle Processing: Hydrophobic Aggregation by Shear Flocculation

This study investigates the hydrophobic aggregation of fine quartz particles through shear flocculation induced by dodecylamine in aqueous solutions. The effect of stirring speed, collector concentration, flocculation time, and pH were investigated. The results showed that the impact of stirring speed on particle aggregation in the absence of a collector is very limited. Quantitative analyses demonstrated that the variation of collector concentration intensified the flocculation process more than the stirring rate. Numerical optimization showed that the large volume occupied by the flocs was 12.3 mL, achieved with a stirring speed of 2135 rpm and dodecylamine concentration of 1.39 × 10−2 mol·L−1. The highest quartz particle aggregation was observed at pH 10.5, corroborating the importance of the non-dissociated amine molecules for particle hydrophobization. High zeta potential values did not result in reducing aggregation, indicating that hydrophobicity was the governing factor in the shear flocculation process.

Use of ultrasonic treatment as a pre-phase in the shear flocculation process

The use of ultrasonic energy has mostly been investigated for the flotation process in mineral processing, but its application to flocculation with collectors is extremely limited. Therefore, in this study, the effect of ultrasound in the shear flocculation technique, was intended to be revealed by using a celestite sample. The initial studies carried out for this purpose showed that in the absence of any reagent, the ultrasonication decreased the surface charge of the mineral, which caused the coagulation of the celestite suspension. In this scope, the short application of ultrasound at high power (i.e., 2 min batch regime and 150 W) provided a more positive effect. In the flocculation process carried out with collectors, the use of ultrasonic energy as a pre-phase for the suspension enhanced the aggregation of celestite particles. This result also fits well with the rise in the contact angle and the decrease in the zeta potential of the mineral due to the ultrasound. However, when the ultrasound was applied directly to the flocculation phase (ultrasound-induced flocculation only), the aggregation of celestite particles was affected adversely. Consequently, it can be said that in the shear flocculation process, the ultrasonic treatment should be used as a pre-phase for mineral suspensions. In this case, the flocculation of fine mineral particles in suspensions with surfactants can be improved by ultrasonic processing.

The Challenges and Prospects of Recovering Fine Copper Sulfides from Tailings Using Different Flotation Techniques: A Review

Flotation is a common mineral processing method used to upgrade copper sulfide ores; in this method, copper sulfide mineral particles are concentrated in froth, and associated gangue minerals are separated as tailings. However, a significant amount of copper is lost into tailings during the processing; therefore, tailings can be considered secondary resources or future deposits of copper. Particle–bubble collision efficiency and particle–bubble aggregate stability determines the recovery of target particles; this attachment efficiency plays a vital role in the selectivity process. The presence of fine particles in the flotation circuit is because of excessive grinding, which is to achieve a higher degree of liberation. Complex sulfide ores of markedly low grade further necessitate excessive grinding to achieve the maximum degree of liberation. In the flotation process, fine particles due to their small mass and momentum are unable to collide with rising bubbles, and their rate of flotation is very slow, further lowering the recovery of target minerals. This collision efficiency mainly depends on the particle–bubble size ratio and the concentration of particles present in the pulp. To overcome this problem and to maintain a favorable particle–bubble size ratio, different techniques have been employed by researchers to enhance particle–bubble collision efficiency either by increasing particle size or by decreasing bubble size. In this article, the mechanism of tailing loss is discussed in detail. In addition, flotation methods for fine particles recovery such as microbubble flotation, column flotation, nanobubble flotation, polymer flocculation, shear flocculation, oil agglomeration, and carrier flotation are reviewed, and their applications and limitations are discussed in detail.

Effect of high-speed shear flocculation on the flotation kinetics of ultrafine microcrystalline graphite

A novel process combining high-speed shear flocculation and flotation (SFF) was proposed to beneficiate ultrafine microcrystalline graphite (MG). The effect of high-speed shear flocculation on the flotation kinetics of ultrafine MG was investigated extensively by comparing with conventional flotation process. The flotation kinetics of these two processes were fitted with six flotation kinetic models using 1stOpt statistical analysis software. The results show that the flotation rate of MG in the SFF process is about 3 times as fast as that in the conventional flotation process based on the first-order model with rectangular distribution of flotabilities. On one hand, the high-speed shear flocculation process resulted in increasing size of graphite aggregates. On the other hand, it generated decreasing size of kerosene droplets, which in turn benefited the increase in the size of graphite aggregates due to the improved hydrophobicity of graphite particle surface. The increased aggregates were responsible for the increase in flotation rate of MG in the SFF process. In addition, the SFF process could also improve the concentrate grade and recovery of MG in comparison with conventional flotation. The utilization of the SFF technology to separate ultrafine MG is of great potential in industrial applications.

An Extended Entropic Model for Cohesive Sediment Flocculation in a Piecewise Varied Shear Environment.

In this study, an extended model for describing the temporal evolution of a characteristic floc size of cohesive sediment particles when the flocculation system is subject to a piecewise varied turbulent shear rate was derived by the probability methods based on the Shannon entropy theory following Zhu (2018). This model only contained three important parameters: initial and steady-state values of floc size, and a parameter characterizing the maximum capacity for floc size increase (or decay), and it can be adopted to capture well a monotonic pattern in which floc size increases (or decays) with flocculation time. Comparison with 13 literature experimental data sets regarding floc size variation to a varied shear rate showed the validity of the entropic model with a high correlation coefficient and few errors. Furthermore, for the case of tapered shear flocculation, it was found that there was a power decay of the capacity parameter with the shear rate, which is similar to the dependence of the steady-state floc size on the shear rate. The entropic model was further parameterized by introducing these two empirical relations into it, and the finally obtained model was found to be more sensitive to two empirical coefficients that have been incorporated into the capacity parameter than those in the steady-state floc size. The proposed entropic model could have the potential, as an addition to existing flocculation models, to be coupled into present mature hydrodynamic models to model the cohesive sediment transport in estuarine and coastal regions.

Fractal dimension of large aggregates under different flocculation conditions

The two-dimensional fractal dimension (Df) of large aggregates of kaolin (>540μm) during the shear flocculation process for kaolin solution was investigated using non-intrusive in situ image-based acquisition system. Separate experiments were also carried out for three different sized sub-ranges of large aggregates (0.540–1.125mm; 1.125–1.750mm; 1.750–2.375mm). Digital images were taken at a frequency of 10Hz for 10s for each different pairs of gradients of velocity (Gf) of 20 and 60s−1 and flocculation times of 2; 3; 4; 5; 10; 20; 30; 60; 120 and 180min. For the same conditions, particle size distribution (PSD) was also determined. Under the investigated conditions, the lowest Gf produced the greatest Df (1.69) at a flocculation time of 30min for the whole range of aggregates. Also, the evolution of the longest length of aggregate (l) and Df with time, showed that the dynamic steady-state was reached at different times for each shear rate and l ranges. However, Df varied for each size sub-range (ca. 1.1 to 1.8). Finally, the behavior of the aggregate structure may be understood by the predominance of different aggregation mechanisms such as cluster-cluster for Gf of 60s−1 and particle-cluster for Gf of 20s−1.

Effect of energy input on flocculation process and flotation performance of fine scheelite using sodium oleate

We have investigated the effect of energy input on the flocculation process and flotation behavior of fine scheelite of less than 10µm size. Sodium oleate was used as a dual-function reagent, acting as flocculant and collector. Energy input in shear flocculation was controlled in a four-baffle cylindrical tank with a four-blade impeller by changing the agitation speed. The flocculation process was investigated by measuring continuous transformations in size distribution and observing floc shape. The results show that with increasing energy input, the size distribution of fine scheelite transforms from unimodal to bimodal. The flocs produced tend to possess more branches with low energy input and tends to become globule-like with high energy input. A parameter termed the flocculation degree was introduced to quantify the flocculation process as a function of energy input. The flocculation degree with increasing energy input reveals the aggregation order of different size fractions (all less than 10µm) when forming flocs. The flotation rate of flocs formed with different energy input was studied. The results demonstrate that the flotation rate is closely related to energy input and also, exhibits an intimate correlation with flocculation degree. These results could potentially be used to routinely monitor the flotation performance of fine particles in operating plants when shear flocculation is used.

Gamma processes of shear flocculation, oil agglomeration and liquid–liquid extraction

Gamma flotation process is characterized by emphasis on the control of solution surface tension and the separation of minerals in suspension with this technique is based on the differences in wettability of minerals. The wettability properties of mineral surfaces can be defined in terms of their values of critical surface tension of wetting (γc) as a quantifying parameter, which is an essential property to achieve selectivity in surface chemistry-based separation processes. That is, the gamma flotation technique utilizes the differences in the critical surface tension of wetting (γc) of minerals. Similar to the flotation method, shear flocculation, oil agglomeration and liquid–liquid extraction processes also utilize differences in wettability of minerals. Therefore, the separations of minerals by the control of surface tension in the shear flocculation, oil agglomeration and liquid–liquid extraction methods can be provided. In this study, the separations of some minerals with these processes have been investigated by using the control of the solution surface tension and the successful results could be reached. Consequently, these new separation processes have been defined as ‘gamma shear flocculation’, ‘gamma oil agglomeration’ and ‘gamma liquid–liquid extraction’.

Two-stage shear flocculation for enrichment of fine boron ore containing colemanite

The enrichment of fine boron ore containing colemanite mineral was investigated using shear flocculation, two-stage shear flocculation, column flotation and floc flotation techniques. In these fine particle processing methods, sodium dodecyl sulfate (SDS) and Aero 801 were used as surfactant for colemanite. Also, sodium pyrophosphate and sodium hexametaphosphate were employed to improve the selectivity of the processes. The highest grade of the colemanite concentrate was obtained with two-stage shear flocculation method using Aero 801 and sodium hexametaphosphate. Under the optimum conditions, a concentrate of 38.65% B2O3 could be recovered by two-stage shear flocculation from the ore containing 26.98% B2O3.

Influence of Hydrophobicity on Agglomeration of Dolomite in Cationic-Anionic Surfactant System

In this study the modified procedure of the oil agglomeration process was carried out, where the emulsion of dodecylammonium hydrochloride (DDAHCl) solution and kerosene was added to the mineral suspension. The aim of this work was to research the oil agglomeration of dolomite mineral by the contact angle, zeta potential and surface free energy measurements. The relationship between the investigated parameters and the oil agglomeration as well as shear flocculation was revealed. The mechanism of oil agglomeration of hydrophilic particles in cationic-anionic surfactant system has been proposed. It was concluded that oil droplets interact rather with aggregates of particles modified by anionic surfactant than the single mineral particles as was explained for naturally hydrophobic particles.

Investigation of shear flocculation behaviors of colemanite with some anionic surfactants and inorganic salts

The variations of shear flocculation of colemanite mineral with sodium oleate and sodium dodecyl sulfate (SDS) as anionic surfactants with suspension pH, surfactant concentration, stirring speed, and flocculation time have been investigated. It was determined that sodium oleate was more effective in the flocculation than SDS and the colemanite particles could be flocculated by oleate in the broad pH range. Also, a stirring speed of 500 rpm and a flocculation time of 3 min were required to achieve the maximum flocculation degree of colemanite particles. The effects of magnesium, barium, aluminum, and ferric chlorides as inorganic salts on the shear flocculation of colemanite suspension were also studied. In the presence of these cations, the flocculation degrees of colemanite suspension reached high values at particular conditions. However, some differences in the behavior of flocculation of colemanite mineral were observed depending on pH, cation concentration, type of surfactant and inorganic salt.

Correlation of Flocculation and Agglomeration of Dolomite with its Wettability

Wettability is an important parameter which affects the shear flocculation and oil agglomeration behaviors of minerals. The critical surface tension of wetting (γc) as a wettability parameter describes wetting characteristics of any mineral. In this study, the correlation of shear flocculation and oil agglomeration processes of dolomite with its wettability parameter is investigated. The experimental studies have indicated that these processes improved with decreasing wettability depending on the increase of oleate adsorption despite a simultaneous increase in the zeta potential of dolomite. On the other hand, the flocculation and agglomeration of dolomite decreased with decreasing surface tension and did not occur below a particular value of surface tension, corresponding to the critical surface tension of wetting (γc) and the critical solution surface tension (γc-a) values, respectively. Also, the γc-a values are slightly higher than the γc values, indicating that the agglomeration of the particles requires a lower wettability.

Shear Flocculation and Flotation of Hematite

Sodium alkylsulfonate as collector was used to float hematite by shear flocculation flotation. The effect of the particle size, pulp pH, depressor, shearing strength and shearing time on shear flocculation flotation for hematite was investigated. And the main mechanism of shear flocculation flotation for hematite was analysed and studied by means of interface double layer theory, DLVO and EDLVO theory, shear flocculation theory and basic principles of collision theory. The results show that on the condition of collector usage 4 kg/t, pH of pulp 3, grinding fineness(-0.037mm) 90%, conditioning time 2min, shearing strength 2000r/min and shearing time 7min, the higher iron recovery of 92.4% is obtained. And induced hydrophobic hematite is formed by means of sodium alkylsulfonate and then collision probability of fine hematite is increased to make hydrophobic particles overcome potential barrier and form hydrophobic flocs by direct contact under stirring intensively.

Role of hydrophobicity and surface tension on shear flocculation and oil agglomeration of magnesite

This paper describes the role of hydrophobicity and surface tension on the shear flocculation and oil agglomeration of magnesite mineral. The experimental results have demonstrated that these processes were closely correlated with the particle hydrophobicity; however, they were not lowered by increasing the surface charge due to sodium oleate adsorption. Also, higher degrees of hydrophobicity were required to achieve the maximum aggregation in the oil agglomeration of magnesite fines in comparison to its shear flocculation. On the other hand, these aggregation processes decreased depending on the decrease in the contact angle with decreasing surface tension. Eventually the shear flocculation and oil agglomeration of fine particles in the suspension did not take place below a particular value of surface tension, corresponding the critical surface tension of wetting ( γ c) and the critical solution surface tension ( γ c-a) values, respectively.

Comparison of stages in oil agglomeration process of quartz with sodium oleate in the presence of Ca(II) and Mg(II) ions

The oil agglomeration of quartz with sodium oleate in the presence of calcium and magnesium ions comprises three consecutive stages: adsorption of cations onto quartz surfaces, which leads to coagulation of the suspension, shear flocculation with sodium oleate and finally, agglomeration of flocs by kerosene. The effects of pH and cation concentration on these stages were investigated and the results were presented comparatively. It was found that all the stages of oil agglomeration of quartz exhibited sharp dependences on pH and cation concentration. That is, these stages generally took place in the pH and concentration ranges in which hydroxy complexes of the cations existed in the suspension. In the case of magnesium ion, the coagulation, shear flocculation and especially oil agglomeration of quartz improved after precipitation of hydroxide. These species of calcium and magnesium ions formed at high pH were adsorbed on the negatively charged surface of quartz, as a result of which the adsorption of sodium oleate became possible and thus the shear flocculation of the particles was achieved. Thereafter, the hydrophobic quartz flocs could be agglomerated by kerosene as bridging liquid. The increase in the shear flocculation efficiency depending on the increase of surface hydrophobicity enhanced the oil agglomeration of quartz with kerosene. The maximum recoveries for all the stages of the quartz were obtained in the presence of 10 −3 M magnesium and 5 × 10 −3 M calcium ions at pH 11. However, some differences in the behavior of shear flocculation and oil agglomeration of quartz suspension were observed above 10 −3 M concentration of magnesium ion.

Application of a statistical design method to the shear flocculation of celestite with Na-Oleate

In this study, the Box–Wilson statistical experimental design method was employed to evaluate the effects of important variables such as amount of Na-Oleate, salt (MgCl 2) concentration and stirring speed on the shear flocculation of celestite. Response function coefficients were determined by the regression analysis of experimental data and the predictions were found to be in good agreement with the experimental results. The optimum Na-Oleate amount, MgCl 2 concentration and stirring speed were determined as 1.5 kg/t, 0.1 M and 500 rpm, respectively, when considering flocculation recovery.

Correlation of shear flocculation of some salt-type minerals with their wettability parameter

This paper considers the importance of surface hydrophobicity in the shear flocculation process and presents a correlation between the shear flocculation and the wettability parameter for barite, celestite and calcite as salt-type minerals. The critical surface tension of wetting ( γ c) as a wettability parameter describes wetting characteristics of any mineral. The variation of the shear flocculation behaviours of barite, celestite and calcite with sodium oleate concentration in various methanol solutions was investigated. The shear flocculation of these minerals in the methanol solutions increased rapidly towards the optimum surfactant concentration, and thereafter remained relatively constant or increased slightly. On the other hand, the shear flocculation of the minerals decreased with increasing methanol concentration, depends on decreasing surface tension. The γ c values of these minerals as a function of surfactant concentration were determined using a shear flocculation approach. It was found that the γ c values did not change much at surfactant concentrations above the optimum. This result provides a reason for the observed lack of significant increase in the shear flocculation of the mineral suspensions when surfactant concentrations higher than the optimum are used. Furthermore, a strong correlation between the effective shear flocculation and the critical surface tension of wetting ( γ c) value was established. As the effective shear flocculation of these salt-type minerals increased sharply below a particular γ c value, it was not much improved after reaching the γ c value obtained at the optimum concentration of sodium oleate.

Shear flocculation of celestite with anionic surfactants and effects of some inorganic dispersants

Shear flocculation characteristics of celestite (SrSO 4) mineral have been investigated using sodium dodecyl sulfate (SDS) and Aero 845 as anionic surfactants. The celestite suspension could be flocculated by SDS and Aero 845 in the broad pH range. However, these surfactants were slightly more effective on the celestite suspension at a pH of 7. The shear flocculation of celestite with SDS and Aero 845 increased rapidly with increasing surfactant concentration. However, it decreased at SDS concentrations higher than 45 mg/dm 3, and eventually stabilization of the suspension took place at concentration values above approximately 80 mg/dm 3. From the experiments carried out to determine the effects of stirring speed and flocculation time on the shear flocculation of celestite suspension, it was found that a stirring speed of 500 rpm and a flocculation time of 3 min were required to achieve the maximum aggregation degree of celestite particles. The effects of sodium silicate, sodium phosphate and sodium polyphosphate used as inorganic dispersants on the shear flocculation of celestite were also studied. Sodium silicate strongly prevented the shear flocculation of celestite with SDS. However, the dispersive effect of sodium silicate was low in the presence of Aero 845. In the case of sodium polyphosphate, a dispersive effect on the celestite suspension was not observed for both surfactants. On the contrary, the shear flocculation power values increased slowly in the presence of sodium polyphosphate. In addition, the similar phenomenon also took place for sodium phosphate in the presence of SDS.