Froth Volume Research Articles

Flotation performance and adsorption mechanism of 2-triethylenetetramine methylene-4-nonylphenol to pyrochlore

The flotation performance and adsorption mechanism of 2-triethylenetetramine methylene-4-nonylphenol (TMNP) on pyrochlore were investigated through micro-flotation experiments, zeta-potential tests, contact angle and XPS measurements. Additionally, the frothing properties of TMNP were studied using froth volume and surface tension tests compared with DDA. The flotation results showed that TMNP exhibited strong collecting ability for pyrochlore, but showed no selectivity towards quartz or feldspar. Separation experiments showed sodium aluminium silicate was an effective depressant for the separation of pyrochlore, feldspar, quartz, and calcite. The frothing properties of both TMNP and DDA were correlated with their respective surface tensions. Contact angle experiments demonstrated contact angle increased with increasing concentrations of TMNP and DDA. Zeta potential indicated that TMNP might adsorb onto pyrochlore surfaces through electrostatic attraction and chemical adsorption while DDA only exhibited physical adsorption. XPS data provided further evidence for the chemical adsorption of TMNP onto pyrochlore surfaces.

Gangue Entrainment in Olivine Flotation: Effect of MIBC Dosage on the Mitigation of Lizardite Recovery

Background: Olivine is an important industrial raw material especially for metallurgical applications like foundry sand, refractory, slag conditioning, etc. Loss On Ignition (LOI) value (>1%) is the main specification of olivine ore/concentrate for those areas together with the chemical specifications. Objective: This flotation study was conducted in natural pH condition with Na-oleate as collector to clarify the effect of frother (MIBC) dosage on the LOI value of olivine concentrate. Methods: Characterization of ore sample for this study was made by XRD, XRF and petrographic analyses. Lizardite, a serpentine group mineral, was found to be a hydrated soft fraction of ore sample in addition to hard olivine and pyroxene minerals constituting ore. Results: Finely ground soft lizardite adversely affected the olivine flotation in a way of entraining mechanically into concentrate. LOI value of concentrate was observed mainly to be froth volume depended issue, and therefore, mainly water recovery dependent. LOI value increased proportionally with water recovery at longer flotation time and MIBC dosages indicating the entrainment of lizardite as the suspending hydrophilic component of water phase. Certain rate of the hydrated lizardite mineral was thought to be recovered via hydrophobization, which was clearly seen especially at the initial stages of flotation period in the presence of excess frother. This experimental finding was attributed to similar chemical composition of minerals constituting ore, and accidental activation of lizardite. Conclusions: Lizardite recovery in froth was explained with accidental activation and/or weak attachment of locked particles onto froth bubble although main recovery mechanism was determined to be mechanical entrainment. Olivine concentrate obeying the specifications of metallurgical applications could be obtained at suitable MIBC dosage and flotation time.

The interaction between kaolinite and saline water in affecting the microstructure, rheology and settling of coal flotation products

The low settling efficiency of flotation froth products is a major challenge confronting the coal industry and studies on the effect of interfacial properties of coal flotation products on their rheology and settling behaviours are limited. In this work, the effect of two important variables in coal flotation, the content of kaolinite (a clay mineral) and the water salinity, on the settling of coal flotation products was studied through understanding their microstructures and rheology properties. It was found that network structures in Plateau border of coal froth were generated with the presence of kaolinite recovered through entrainment in coal flotation, while the network structure had the tendency to vanish with the increase of water salinity due to the change in the microstructure of kaolinite. Meanwhile, the storage modulus G' in oscillatory rheology and the volume of froth floating on top of water in settling exhibited the same pattern. With the presence of kaolinite and the increase of water salinity, the value of G' and the volume of froth floating on top of water both increased. However, the effect of kaolinite on the results of rheology and settling was diminished with the increase of water salinity. It was the structure of Plateau border that determined the rheology and settling behaviours of coal flotation products.

An investigation of froth stability in reverse flotation of collophane

In flotation, froth stability strongly influences the separation process, as such stability is linked to the particle size, mineral content and water quality. In this study, the froth stability in the reverse flotation of collophane was investigated by froth stability tests and froth drainage experiments with the cationic surfactant N1-(3-((8-Methylnonyl)oxy)propyl)propane-1,3-diamine (MOPPD). The results indicated that the presence of fine fractions lead to the high froth stability, and the froth stability increased with increases in the mineral content. Furthermore, it was shown that the presence of calcite and dolomite greatly increased the froth stability compared to quartz and fluorapatite. In addition, Ca2+ and Mg2+ dissolved by calcite and dolomite were proved to stabilize the froth structure. On the basis of the froth stability in the reverse flotation of collophane, a strategy for controlling the froth stability through desliming by sedimentation and flotation before quartz removal was proposed. Flotation tests showed that the concentrate grade increased to 28.06% and the froth volume of tailings greatly decreased to 920 mL compared with the values of 24.13% and 4200 mL, respectively, for direct flotation. Overall, the results confirmed that the proposed strategy is crucial for managing froth during quartz removal from collophane.

Effects of Fine Coal Particles on the Recovery of Coarse Coal in Collectorless Coal Flotation

ABSTRACT The effects of fine coal (<74 μm) of four density fractions, namely <1.4, 1.4–1.6, 1.6–1.8, and >1.8 g/cm3, on the recovery of coarse coal (−500 + 250 μm) in collectorless flotation were studied in this article. It was found that the fine coal of all density fractions increased the coarse coal recovery except for the fine coal of <1.4 g/cm3 density fraction with the low mixing ratio in the feed. By analyzing the coarse coal yield, water recovery, concentrate weight composition, froth gray value, and froth height over weir, two mechanisms of increasing the coarse coal recovery by fine coal particles were, respectively, put forward for hydrophobic and hydrophilic particles. The hydrophobic particles mainly affected the dynamic froth stability by hydrophobicity and the overflowing froth volume by the amount of floatable particles, while the hydrophilic particles affected water drainage by the entrained particles in the froth network.

Effects of particle size and concentration on bubble coalescence and froth formation in a slurry bubble column

A new approach for simulating the formation of a froth layer in a slurry bubble column is proposed. Froth is considered a separate phase, comprised of a mixture of gas, liquid, and solid. The simulation was carried out using commercial flow simulation software (FIRE v2014) for particle sizes of 60–150μm at solid concentrations of 0–40vol%, and superficial gas velocities of 0.02–0.034m/s in a slurry bubble column with a hydraulic diameter of 0.2m and height of 1.2m. Modelling calculations were conducted using a Eulerian–Eulerian multiphase approach with k–ε turbulence. The population balance equations for bubble breakup, bubble coalescence rate, and the interfacial exchange of mass and momentum were included in the computational fluid dynamics code by writing subroutines in Fortran to track the number density of different bubble sizes. Flow structure, radial gas holdup, and Sauter mean bubble diameter distributions at different column heights were predicted in the pulp zone, while froth volume fraction and density were predicted in the froth zone. The model was validated using available experimental data, and the predicted and experimental results showed reasonable agreement. To demonstrate the effect of increasing solid concentration on the coalescence rate, a solid-effect multiplier in the coalescence efficiency equation was used. The solid-effect multiplier decreased with increasing slurry concentration, causing an increase in bubble coalescence efficiency. A slight decrease in the coalescence efficiency was also observed owing to increasing particle size, which led to a decrease in Sauter mean bubble diameter. The froth volume fraction increased with solid concentration. These results provide an improved understanding of the dynamics of slurry bubble reactors in the presence of hydrophilic particles.

Frothability characterization of residual organic solvents

Organic solvents were evaluated through the determination of froth volume and bubble collapse rate in a froth column meter under various solvent dosages and aeration rate levels. There is a non-linear relationship between the froth volume and the gas flow rate for polyglycol ether type solvents. It is inappropriate to apply the concept of linearity retention time to describe the frothing characteristics of polyglycol ethers. Two new parameters are derived to characterize the foam stability and non-persistency of the frothers. The new parameters are initial dynamic froth index (IDFI) and initial dynamic froth collapse rate (IDCR). IDFI represents the froth volume formation properties, and can be used to relate to the ultimate recovery, Rm, and the flotation rate constant, K. IDCR describes the non-persistency of the froth, and can be used to relate to the quality of flotation concentrates. IDFI value depends on chemical structure and molecular weight of a solvent. Increasing solvent molecular weight and number of hydrophobic groups increases the IDFI value. Both ultimate recovery and flotation rate constant can be maintained at a desirable level, if the solvent dosage is applied in the amount to give the same product value of IDFI and solvent dosage. The selection of potential frothers from solvents tested is made by using IDFI and IDCR and comparing with laboratory fine coal flotation performance.

The behaviour of wash water injected into a froth

Wash water is introduced into flotation froths to reduce the amount of entrained material reporting to the product. However, the behaviour of wash water in a froth is not well understood at present, and detailed information is sparse. The design of wash water delivery systems is currently based largely on trial and error. In the present study, experiments were conducted in a two-dimensional froth column to observe the movement of wash water in a froth, using various types of injector. Thus wash water was injected through a vertical pipe placed above the froth; through the same pipe immersed in the froth; and through a tee that resulted in two opposed horizontal jets. The movements of the wash water were observed, and quantitative liquid-fraction maps obtained, for each system. With the horizontal jets, vortex pairs were observed to form in the froth as a result of the wash water injection. In terms of their ability to spread wash water in the horizontal direction, the horizontal jets performed better than the vertical jet within the froth, which gave better results than the same jet falling on the free surface of the froth. The results show that whatever system is used, considerable back-mixing occurs between the froth and the added wash water, in the froth layer. Thus it is never possible to remove all the gangue particles from the flotation product. The best that can be done is to minimise the recovery of gangue by finding the optimum combination of the volume of froth beneath the injection point, the volume of froth above the injection point, and the gas and water flow rates. These observations are independent of the type of wash water distributor used.

Dynamic froth stability in froth flotation

A new measure for froth stability is introduced in this work, based on a dynamic stability test for non-overflowing froth columns. The dynamic stability factor represents the lifetime of a bubble in the froth, and is defined as the ratio of the total volume of froth at equilibrium to the volumetric gas rate introduced into the system. Experiments have been carried out at laboratory scale to measure the dynamic stability factor under different operating conditions. Air flowrate and frother concentration were the key operating variables. It was found that the equilibrium height and the dynamic stability factor depend significantly upon both the air flowrate and the frother concentration. Also, the dynamic stability factor and the fraction of air overflowing as unbroken bubbles in batch flotation tests were related and can be used to establish a stability criteria. These measurements will also allow a clearer quantitative link to be formed between froth stability with froth structure and flotation performance.

The modelling of froth zone recovery in batch and continuously operated laboratory flotation cells

This paper proposes an integrated methodology for modelling froth zone performance in batch and continuously operated laboratory flotation cells. The methodology is based on a semi-empirical approach which relates the overall flotation rate constant to the froth depth (FD) in the flotation cell; from this relationship, a froth zone recovery ( R f) can be extracted. Froth zone recovery, in turn, may be related to the froth retention time (FRT), defined as the ratio of froth volume to the volumetric flow rate of concentrate from the cell. An expansion of this relationship to account for particles recovered both by true flotation and entrainment provides a simple model that may be used to predict the froth performance in continuous tests from the results of laboratory batch experiments.

Flotation de-inking studies using model hydrophobic particles and non-ionic dispersants

A series of non-ionic alcohol ethoxylated surfactants (with HLB within the range of 11.1–12.5) were used as dispersants during flotation of mondisperse hydrophobised silica particles (representing ink particles) in de-inking formulations. Laboratory scale flotation experiments, contact angle, dynamic surface tension and thin film drainage experiments were carried out. The reduction in dynamic surface tension at the air/solution interface (which is dependent on the adsorption kinetics) followed the order C 10E 6>C 12E 8≈C 12E 6>C 14E 6 and these values were lower than sodium oleate, which is commonly used in de-inking systems. In addition the non-ionics adsorbed on the hydrophobised silica particles reducing the contact angle. These results indicated that the non-ionic surfactant with the highest CMC (C 10E 6) gave (a) the highest rate of adsorption at the air/solution interface (b) the froth with the greatest water content and higher froth volume (c) the lowest reduction in contact angle and (d) the highest flotation efficiency at concentrations above the CMC. It was also observed that flotation occurred, in spite of the fact that thin-film measurements indicated that the adsorption of non-ionic at the air/solution and silica/solution interfaces reduced the hydrophobicity of the particles, as indicated by an increase in stability of the aqueous thin film between the particle and air-bubble. This result suggests that the bubble-ink particle captures mechanism (occurring through rupture of the thin aqueous film separating the interfaces) is not the only mechanism controlling the flotation efficiency and that other parameters (such as the kinetics of surfactant adsorption, foaming characteristics, and bubble size) need to be taken into account. The kinetics is important with respect to the rate of adsorption of surfactant to both interfaces. Under equilibrium conditions, this may give rise to repulsive steric forces between the air-bubble and the particles (stable aqueous thin-films). However, a lower amount of surfactant adsorbed at a freshly formed air bubble or inkparticle (caused by slow adsorption rates) will produce a lower steric repulsive force allowing effective collection of particles by the bubble. Also, it was suggested that the influence of alcohol ethoxylates on bubble-size could effect the particle capture rate and mechanical entrainment of particles in an excessively buoyant froth, which will also play an important role in the flotation recovery.

97/02429 Initial testing of a dynamic column for fine coal flotation

This paper describes the design and initial performance of a dynamic column for fine coal column flotation. A dynamic column is a modified conventional column with the insertion of a series of draft tubes that provide individual mixing stages. The mixing is beneficial in generating small and uniform bubbles over a wide range of frother dosages. It is also beneficial in the control of flotation where the fluctuation of froth volume should be minimized. In the modified design, a vortex-inducing plate is attached to the top of each draft tube to create an artificial vortex. In theory the vortex action is desirable for collecting the light clean coal froth within the inner mixing zone, and for passing it upward to the next draft tube stage. The mineral laden slurry, particularly the pyrite, is accelerated outside the vortex zone by centrifugal force to reach the wall where it is carried downward to the bottom of the column. The draft tubes are arranged in a series to accomplish multistage cleaning. The experimental results showed that this dynamic column has the potential advantage of higher throughput and better product recovery as well as improved product quality.

An advisory package for flotation operators using a real-time expert system

The operation and control of a large flotation circuit demands the attention and constant supervision of experienced operators. Although the advances of on-stream analysis now provide improved monitoring of the flotation circuit, skilled operators still rely on their experience to recognize and respond to visual characteristics of the froth in order to implement appropriate actions to maintain stable process outputs. The texture, color, bubble zize and froth volume are features that an experienced operator uses to develop an operating philosophy suitable to current or predicted circuit conditions. Most experienced operators are willing to pass their experience on to new or less experienced operators, but due to the personal classifications and heuristic nature of the rules of thumb used, new staff are often left with a confused picture of the process. This picture is made more complex by the fact that most flotation operators have to train new staff in addition to their existing duties, so several experienced operators will be called upon to guide the trainee. The development of a standardized expert tutor and advisory system, implemented at Highland Valley Copper are described in this paper.

A study of the froth phase in large-scale pyrite flotation cells

The behaviour of mineral particles and water in the froth phase of large-scale flotation cells has been studied by means of a mathematical model. The model considers the distribution of air over the pulp-froth interface, and accounts for the fact that only a certain fraction of the total volume of froth is utilized efficiently for the transport of mineral particles from the pulp to the concentrate. On-site testwork was carried out on a rougher and a cleaner cell at a pyrite flotation plant. It was found that the ratio of solids to water decreased significantly with increasing height in the rougher froth, but increased in the cleaner froth. While the behaviour of the floating fractions of the coarse particle sizes in the rougher cell was similar in the main body of the froth and in the region bordering the concentrate weir, results indicated that the recovery of fines was largely due to their transportation in the froth close to the weir. In the cleaner froth, however, the fine particles were affected more adversely by the froth conditions in the region next to the concentrate weir than the coarser particles.

Froth density profiles and froth height on perforated plate.

Some features of froth density distribution on a perforated plate and their effects on froth height are discussed both experimentally and theoretically. The following results are obtained: 1) Horizontal profiles of froth density in the region between the crest of outlet weir and the froth surface are uniform, while those near the plate surface are non-uniform. The vertical profiles of froth density in the region where the horizontal profiles are uniform are explained by a theoretical equation derived on the assumption that the sum of potential and kinetic energies of froth volume is minimum under steady-state conditions. 2) By this equation mentioned above, the height of the region between the froth surface and the crest of outlet weir is found to be proportional to the square root of the liquid flow rate. This relation is almost independent of the gas flow rate.

Frothing Characteristics of Sodium Oleate Solutions

New index (F) was proposed in order to express the frothing characteristics of surfaceactive agents.F=Vf/V2Where, Vf is the froth volume discharged per unit time (cm3/min), and V2 is the flow rate of the gas sended to form froth (cm3/min).Using this index F, the frothing characteristics of sodium oleate (Na-ol.) solutions were determined. Then the effect of MIBC (4-methyl 2-pentanol) and of the height of froth layer on the frothing characteristics of Na-ol. solutions were investigated.The results were as follows.1) The frothing characteristics of Na-ol. solutions (F) decreased rapidly under the concentration of 0.2 g/l of Na-ol.2) When small quantities of MIBC were added to 0. 2 g/l Na-ol. solution, the value of F increased, although it decreased rapidly over the concentration of 10 ml/l of MIBC.3) The heigher the froth layer, the smaller the value of F.4) Addition of small quantities (under 5 ml/l) of MIBC to 0.5g/l Na-ol. solution, didn't decrease its frothing characteristics though the froth layer became heigher.

Attempts to determine the liquid—film coefficient for physical absorption and effective interfacial area in a sieve plate column by the chemical method

Values of the liquid—side mass transfer coefficient, k L and the interfacial area, a per unit volume of froth on a sieve plate (perforated area 5·5%) were found using the technique of absorption accompanied by irreversible pseudo-first order reaction. The experiments were carried out with several reacting systems, for which the attained values of k L and a were 0·17–0·27 cm/sec and 1·97–2·28 cm 2/cm 3 respectively. A method has been employed, which enables these values to be determined without the necessity of measuring kinetic constants. The results confirmed that the Danckwerts equation could be used to predict rates of absorption in sieve plate columns.