Hallimond Tube Research Articles

Flotation of zinc oxide minerals from low-grade tailings by oxine and dithizone using the Taguchi approach

The main purpose of this study was to find the optimum values for factors affecting the Zn recovery rate using oxine or dithizone as a chelating agent collector during flotation in a Hallimond tube. Eight control factors, including four levels of pH, oxine/dithizone, corn starch, sodium thiosulfate, sodium citrate, sodium silicate, conditioning and floating durations were considered in a Taguchi experimental design technique. An L32 orthogonal array was applied to determine the signal-to-noise (S/N) ratio. Analysis of variance (ANOVA) was used to determine the optimum conditions and the most significant parameters affecting the reaction rate. Analysis of the experiments using the Taguchi approach indicated that pH had the highest contribution to the recovery rate of zinc oxide particles. The results showed that the recovery rate of zinc increased by 43.4 ± 3.0% and 24.9 ± 3.2% using oxine and dithizone, respectively, under optimum conditions with a confidence level of 90%.

Flotação direta de minério de ferro com oleato de sódio

O objetivo desse trabalho foi estudar a possibilidade de concentração de minério de ferro por flotação direta, usando oleato de sódio como coletor dos minerais de ferro e o metassilicato de sódio como depressor da ganga silicosa. Após a caracterização das amostras minerais e do minério, foram feitos estudos fundamentais, que englobaram a determinação do potencial zeta dos minerais hematita e quartzo, cujos valores de PIE ocorreram em pH 7,5 e 1,8, respectivamente. Os ensaios de microflotação, em tubo de Hallimond modificado, determinaram as condições de maior flotabilidade da hematita, 50 mg/L de oleato de sódio em pH 7, e do quartzo, 70 mg/L de oleato de sódio em pH 9. Os ensaios de microflotação, ainda mostraram que o metassilicato de sódio foi mais efetivo na depressão da hematita que na depressão do quartzo. Os ensaios de flotação em bancada confirmaram esse comportamento, ou seja, o metassilicato de sódio não propicia separação seletiva entre a hematita e o quartzo durante a flotação. O melhor concentrado fornecido pela flotação direta da amostra de minério de ferro, cujos teores de Fe e SiO2 eram, respectivamente, de 35,34 e 48,02%, foi obtido usando-se dosagens de 600 g/t de metassilicato de sódio e 1200 g/t de oleato de sódio: recuperação metalúrgica de Fe de 88%, teor de Fe de 58,1% e teor de SiO2 de 14,4%.

Zeta-potential and flotability of the scheelite mineral in different type of waters, Part 2: Flotability

The aim of this work was to study floatability of the mineral sheelite from mine 'Rudnik', central Serbia. Flotation tests of the mineral in a Hallimond tube cell were carried out in four different types of water, namely: tap water, distilled water, rain water and spring water. All types of water had different hardness and conductivity as well as natural pH values. It was found that the flotability of mineral scheelite depends on the hardness and electro-conductivity of the chosen type of water as well as on Ca2+ content. Also, it was found the floatability of mineral depends on the scheelite particle size fraction used in microflotation experiments. Presented results may be useful for proper selection of type of water, as well of the type of reagents used in flotation processes.

Floatability of apatites and gangue minerals of an igneous phosphate ore

The presence of different apatite types is characteristic of igneous phosphate deposits. The flotation performances of primary and secondary apatites occurring in phoscorites, weathered phoscorites and pyroxenites were investigated. As a contribution towards the understanding of the behaviour of the flotation system, the major gangue minerals were also selected for the study: quartz, a pyroxene (augite), altered micas (vermiculite), calcite and dolomite. Zeta potential curves for all the above mentioned mineral species were determined as a function of pH, pCa and pMg. Microflotation experiments were performed in a modified Hallimond tube at different pH levels in the presence of sodium oleate as collector and corn starch as depressant.

Carrier-microencapsulation using Si–catechol complex for suppressing pyrite floatability

Pyrite (FeS 2) is a common sulfide mineral associated with valuable metal minerals and coal, and it is rejected as a gangue mineral using physical separation techniques such as froth flotation and discharged into tailing pond. In the flotation, pyrite is frequently entrapped in the froth due to its hydrophobic nature. Formation of acid mine drainage due to the air-oxidation of pyrite in the tailing pond is also a serious problem. The authors have proposed carrier-microencapsulation (CME) as a method for suppressing both the floatability and oxidation of pyrite. In this method, pyrite is coated with a thin layer of metal oxide or hydroxide using catechol solution as a carrier combined with metal ions. The layer converts the pyrite surface from hydrophobic to hydrophilic and acts as a protective coating against oxidation. The present study demonstrates the effect of CME using Si–catechol complex to suppress the pyrite floatability: The bubble pick-up experiments showed that attachment of pyrite particles to air bubble is suppressed by the CME treatment at pH 4–10, Si–catechol complex concentration over 0.5 mol m −3 and treatment time within 2 min. The Hallimond tube flotation experiments showed that the pyrite floatability is suppressed by the CME treatment even in the presence of typical flotation collectors such as kerosene and xanthate. SEM-EDX analysis confirmed that Si present on the pyrite surface treated by Si–catechol complex, implying that SiO 2 or Si(OH 4) layer formed by the CME treatment convert the pyrite surface hydrophobic to hydrophilic.

CELESTITE-GYPSUM SEPARATION BY FLOTATION

The celestite ore from Sivas, Turkey which was subjected to this experimental study contained mainly celestite and gypsum as gangue minerals. Flotation behaviour of pure minerals, celestite and gypsum was investigated using oleate and sulphonate as collectors in a Hallimond tube. The zeta potential values of both minerals were measured with respect to pH in an attempt to explain the flotation mechanism of the collectors. Hallimond tube tests conducted with oleate as a collector suggested that gypsum floated best around pH 6, yet celestite floated best around pH 8.5. On the other hand, in the case of sulphonate, there was not a distinct pH value where gypsum and celestite were best floated. Flotation studies were also carried out in the Denver cell to obtain marketable celestite concentrates from an ore sample from same mine. Parameters such as pH, collector type and dosage were examined using microflotation tests. Contrary to microflotation test results, oleate was found non selective for celestitegpysum separation, while sulphonate type collector provided better selectivity. At pH 5, a celestite concentrate with 93.85% SrSO4 content was produced at 78.4% recovery using 2000 g/ton sulphonate.Le minerai de célestine de Sivas en Turquie, soumis à cette étude expérimentale, contient principalement de la célestine et du gypse comme minéraux de gangue. Premièrement, on a investigué le comportement de flottation des minéraux purs, la célestine et le gypse, en utilisant de l’oléate et du sulfonate comme collecteurs dans un tube de Hallimond. On a mesuré la valeur du potentiel zéta des deux minéraux par rapport au pH afin d’essayer d’expliquer le mécanisme de flottation des collecteurs. Les essais avec le tube de Hallimond, effectués avec l’oléate comme collecteur, suggéraient que le gypse flottait mieux à un pH autour de 6 alors que le meilleur pH pour la célestine était d’environ 8.5. D’un autre côté, dans le cas du sulfonate, il n’y avait pas de valeur distincte de pH pour une meilleure flottation du gypse ou de la célestine. On a également effectué des études de flottation dans une cellule de Denver pour obtenir des concentrés commercialisables de célestine à partir d’un échantillon de minerai de la même mine. On a examiné des paramètres comme le pH, le type et le dosage de collecteur au moyen d’essais de microflottation. Contrairement aux résultats d’essai de microflottation, on a trouvé que l’oléate n’était pas sélective pour la séparation de la célestine et du gypse alors que le collecteur de type sulfonate fournissait une meilleure sélectivité. À un pH de 5, on a produit un concentré de célestine ayant une teneur de 93.85% en SrSO4 avec une récupération de 78.4% en utilisant 2000 g/tonne de sulfonate.

The effect of lignosulfonates on the floatability of talc

The floatability of talc in the presence of six lignosulfonates was studied in a series of Hallimond tube flotation experiments in the alkaline pH range from about 7 to 11.2. The strongest depression of talc was observed at higher pH values (pH ∼ 11) when lime was used for pH adjustments. The depressing power of lignosulfonates correlated very well with the adsorption density of the polyelectrolytes on the talc surfaces. As the adsorption of lignosulfonates increased, their depressing action was also enhanced. The adsorption data strongly suggest that electrostatic repulsion between the negatively charged talc surfaces and the strongly anionic polyelectrolytes prevents lignosulfonates from adsorbing onto the talc surfaces and depressing the flotation of the mineral. The results demonstrate an “activating” role of calcium ions in the depression of talc by lignosulfonates. Calcium species on the talc surface appear to act as adsorption sites for the anionic polyelectrolytes, particularly at higher pH values adjusted with lime when increasing amounts of specifically-adsorbing calcium hydroxy-cations start appearing in solution.

Floatability of chalcopyrite and molybdenite in the presence of lignosulfonates. Part II. Hallimond tube flotation

The effect of six lignosulfonates on the Hallimond tube flotation of chalcopyrite and molybdenite was studied as a function of pH, with the use of common pH modifiers (soda ash, potassium hydroxide, and lime). By comparing the flotation results with the adsorption data collected in Part I of this contribution, it becomes evident that the depression of chalcopyrite flotation takes places only when lignosulfonates adsorb on the mineral surface and, at the same time, a fraction of the xanthate collector is desorbed from the mineral surface. These two conditions are met only at high pH adjusted with lime. The depression of the natural floatability of molybdenite is relatively easy using all six lignosulfonates, but once the mineral is rendered strongly hydrophobic by the addition of an oily collector (dodecane), the depression of molybdenite by lignosulfonates is very difficult and only calcium lignosulfonates, and the highest molecular weight sodium salt, produce significant levels of depression. Overall, the results suggest that it is possible to selectively float chalcopyrite from molybdenite using lignosulfonates by depressing molybdenite. This can be achieved over a wide pH range provided that a pH modifier other than lime is used for pH control. Although the results showed that chalcopyrite flotation and molybdenite depression can be achieved under similar physicochemical conditions, further tests with real ores under industrial conditions have to be carried out with particular attention to the effect of process water quality.

Response of rough and acute surfaces of pyrite with 3-D approach to the flotation

This study presents a new 3-D approach to determine the morphological properties of pyrite particles by Brunauer — Emmett — Teller (BET) nitrogen gas adsorption and Permaran methods. The obtained parameters, which are surface roughness and acuteness, were correlated with the floatability of those mineral particles. The flotation performances of the pyrite particles ground in different mills were also evaluated by a Hallimond tube. The results showed that lower roughness and acuteness values caused higher flotation recoveries for the pyrite particles considered.

Ethyl xanthate adsorption and adsorption kinetics on lead-modified galena and sphalerite under flotation conditions

Infrared attenuated total reflection spectrophotometry, UV data, microelectrophoresis and a Hallimond tube flotation cell have been used to investigate the effect of Pb(II) on the galena and sphalerite surface properties (hydrophobicity and charge of the surface), ethyl xanthate adsorption and ethyl xanthate adsorption kinetics in alkaline medium. It has been found that lead adsorbed on the galena or sphalerite surface as Pb(OH) + and less as Pb 2+ reduced the collectorless galena floatability from pH 7 to 9.5, but had a strong activating effect on natural sphalerite floatability (in pH range 7.6–10.5). Collecting of Pb(II)-modified minerals with K-ethyl xanthate both forms of lead ethyl xanthate, monolayer, Pb EX (chemically adsorbed (EX) −), and multilayer, physically adsorbed Pb(EX) 2, were detected on the mineral surfaces. Sphalerite floated 90–100% in pH range from 7 to 9.5, but galena floated better only from pH 8 to 9.5 (85–95%). The main surface reaction in pH range 8–9.5 is probably the ion-exchange reaction M Pb OH + (EX) − = M Pb EX + (OH) − (M—mineral), which contributes to the chemical adsorption of (EX) − as monolayer Pb EX, on the surface of either mineral. The reaction between Pb(II)-treated mineral and (EX) − ion is a reaction of pseudo-first order with respect to ethyl xanthate (on Pb(II)-modified galena the rate constant is k 1 = 0.711 min −1; on Pb(II)-modified sphalerite k 1 = 0.1014 min −1).

Adsorption of dithiophosphate and dithiophosphinate on chalcopyrite

Electrochemical behavior of chalcopyrite was investigated in the absence and presence of dithiophosphate (DTP) and dithiophosphinate (DTPI), selective thiols against Fe-sulfides in the flotation of sulfide ores, in potentiostatically controlled electrochemical condition. Diffuse reflectance Fourier transformation (DRIFT) spectroscopy was applied to determine the type of adsorbed collector species, and Hallimond tube flotation tests were performed to clarify the role of polarization potential and thiol collectors on the floatability of chalcopyrite. DRIFT spectroscopy study proposed that dithiolate of DTP, (DTP) 2, was the major surface compound formed under oxidizing potentials in slightly acidic and neutral conditions. However, DTP species formed on mineral surface in alkaline condition could not be determined possibly due to heavy surface coating of metal oxyhydroxides. DTPI species formed on chalcopyrite was found to be in the form of CuDTPI + (DTPI) 2. Additionally, presence of adsorbed DTPI, DTPI 0, was also detected. Self-induced floatability was significantly high particularly in slightly acidic condition and decreased by increasing pH due to surface coating of metal oxyhydroxides. Addition of both collectors improved the flotation performance at all pH values. However, the positive effect of DTP at high alkaline pH values was lower than that of DTPI. This was attributed to weak collecting property and lower hydrocarbon chain length of DTP compared to DTPI. Effect of pulp potential could not be observed in slightly acidic condition, but it became apparent at higher pHs. Although better flotation responses were obtained in mildly oxidizing potentials, both collectors enlarged the floatability potential range of chalcopyrite.

Kinetic considerations in the flotation of phosphate ore

Abstract A study was conducted on the flotation with oleic acid of sedimentary phosphates from Sierra Espuña, in the province of Murcia (Spain), also comprising an analysis of the kinetic considerations governing the operation. Two different flotation cells were used for this purpose, i.e. a Hallimond tube and a subaeration cell (Denver D-12). The results achieved with the Hallimond tube show that the rate of mineral flotation is medium to slow, while results with the Denver D-12 cell reveal a faster rate of flotation. It also became clear that the separation of the phosphate and calcareous fractions of the mineral (CaCO 3) is more intense at the very beginning of the operation. The flotation rate constants for mineral sizes between 160 and 325 ASTM mesh were determined, and a linear relationship between flotation rate constant and mineral sizes was shown to exist.

Flotation responses to the morphological properties of particles measured with three-dimensional approach

Morphological properties of barite particles ground by autogenous and ball milling were examined by three-dimensional methods, namely, Brunauer–Emmett–Teller (BET) nitrogen adsorption and Permaran methods in terms of surface roughness and acuteness, respectively. The experimental study showed that autogenously ground products have lower roughness and acuteness. On the other hand, Hallimond tube flotation tests were performed to evaluate the floatability of those particles ground in different environments. Morphological measurements and flotation tests revealed that particles with smooth surfaces gave better floatability.

Attachment of solid particles to air bubbles in surfactant-free aqueous solutions

This paper presents a mechanism to explain the attachment of solid particles to air bubbles in surfactant-free aqueous solutions where both solids and air bubbles have the same sign of zeta potential via investigating the mechanical properties of micro air bubbles and the adsorption of hydroxide on air bubble surfaces. Particle–bubble attachment was measured in a Hallimond tube. The results indicate that purified quartz particles attached to air bubbles in surfactant-free deionised water, and the attachment increased with the pH of the aqueous solutions. The mechanical properties of micro air bubbles in aqueous solutions were measured using a novel micromanipulation technique. It was found that the micro air bubbles were pseudo-elastic and spherical in the solutions. The rigidity of the air bubbles decreased with increasing pH of the solutions. When a moving particle with a certain kinetic energy collided with an air bubble in a surfactant-free aqueous solution, the deformation of the air bubble varied with pH of the solution. In an alkaline solution, the micro air bubble was much softer and the deformation was larger than that in an acidic solution. The larger deformation of the softer air bubble resulted in a large contact area between the solid particle and the air bubble, therefore increasing the attachment, and reducing the rebound. The attachment of purified quartz particles to air bubbles in surfactant-free aqueous solutions was possibly due to hydrogen bond formation. The OH − ions on air bubble surfaces formed hydrogen bonds with silicon and oxygen atoms in ≡Si–O–Si≡ or with the adsorbed OH group on quartz surfaces.

Flotation behaviours of microlite and zircon

In this investigation flotation behaviours of microlite and zircon were studied. Hallimond tube flotation experiments were carried out with pure specimens of microlite and zircon collected from different ore bodies. pH, collector type and depressants were the parameters tested. The results showed that zircon floated in a much better way compared to microlite. Porocoll SAM that is an amphoteric collector was more promising than Porocoll FS-R being a derivate of a fatty acid. Tests indicated that effective separation could be achieved at pH 4. Depressants were observed to deactivate both minerals to some extent.

Study of Microemulsified Systems Applied to Mineral Flotation

An investigation of calcite and fluorite microflotation using microemulsified systems is reported. Several reagents that are commonly used in mineral froth flotation, such as sodium silicate, quebracho, and pH modifiers, were tested. The main objective of this research was to simplify the conventional flotation process by the use of microemulsions. This application is based on their capacity to contain variable amounts of water, oil, and surface-active material in a single phase and their ability to decrease interfacial tension, a fact that favors their application in separation processes. The microflotation assays were accomplished in a modified Hallimond tube under specific operating conditions. The results obtained are pioneer and demonstrated the viability of the use of microemulsions in mineral flotation, leading to an improvement of the conventional process.

Influence of Electrical Double-Layer Interaction on Coal Flotation

In the early 1930s it was first reported that inorganic electrolytes enhance the floatability of coal and naturally hydrophobic minerals. To date, explanations of coal flotation in electrolytes have not been entirely clear. This research investigated the floatability of coal in NaCl and MgCl2 solutions using a modified Hallimond tube to examine the role of the electrical double-layer interaction between bubbles and particles. Flotation of coal was highly dependent on changes in solution pH, type of electrolyte, and electrolyte concentration. Floatability of coal in electrolyte solutions was seen not to be entirely controlled by the electrical double-layer interaction. Coal flotation in low electrolyte concentration solutions decreases with increase in concentration, not expected from the theory since the electrical double layer is compressed, resulting in diminishing the (electrical double layer) repulsion between the bubble and the coal particles. Unlike in low electrolyte concentration solutions, coal flotation in high electrolyte concentration solutions increases with increase in electrolyte concentration. Again, this behavior of coal flotation in high electrolyte concentration solutions cannot be quantitatively explained using the electrical double-layer interaction. Possible mechanisms are discussed in terms of the bubston (i.e., bubble stabilized by ions) phenomenon, which explains the existence of the submicron gas bubbles on the hydrophobic coal surface.

Kinetics and mechanism of coal flotation

The flotation kinetics of coarse coal particles was studied in a modified version of the Hallimond tube at 25 °C using nitrogen as the carrier gas, in the pH range 2–12. The kinetics was followed by measuring the volume of the particles accumulated in the collector tube as a function of time. At each pH, the rate constants were determined at several buffer concentrations and were extrapolated to zero buffer concentration. The observed first-order rate constant was represented as the product of separable constants and functions such as fD, fV and fpH, which depend only on the particle size, gas flow and the pH of the dispersion, respectively. The diameter, D, of the particles was in the range 505–127 μm. The observed rate constant decreased linearly with the diameter of the particles at constant flow and it was calculated that fD=exp(−1.56D). The dependence of fV on the flow is a consequence of the fact that the flotation occurs when a single particle is captured by two bubbles. fV was shown to be independent of the particle diameter. The effect of the pH on the rate of flotation was considered as resulting from the adsorption of protons (or hydroxide ions) by the particles and bubbles through multiple equilibria, assuming that there is no interaction between the binding sites. The pH–rate profile showed that there were two species responsible for the flotation: one stable at pH below 5 and the other at high pH. Comparison of fV, fD and fpH for the flotation of coal and pyrite allowed the prediction of the optimum conditions for the separation of mixtures of these particles by flotation.

Excess nonequilibrium collector adsorption and flotation rates

Experiments using an optically polished Pyrex disk and aqueous dodecylammonium acetate (DAA) films showed that the velocity with which the films recede increases markedly if the runs are repeated at short time intervals, where equilibrium cannot be reattained. This results from DAA molecules being desorbed from the disappearing liquid-air interface and being deposited on the solid-air interface being formed. Controlled experiments with Pyrex particles in a modified Hallimond tube showed a similar increase in flotation rate, again due to excess adsorption of DAA molecules that were transferred to the solid-air interface from the bubble on contact.

The flotation separation of pyrite from arsenopyrite using hexyl thioethylamine as collector

The floatability of pyrite and arsenopyrite was studied using sodium ethyl xanthate (NaEX), potassium amyl xanthate (KAX) and hexyl thioethylamine hydrochloride (HTA). The experiments were conducted on individual minerals and on the mixtures as a function of pH and collector concentration employing Hallimond tube and bench flotation equipment. The performance of HTA, which is an amine type cationic collector, was found to be distinctively good at alkaline pH values unlike xanthates that give good recoveries at acidic pH region. The preliminary work showed that the best separation could be achieved with HTA by the selective flotation of pyrite. Separation tests using HTA were carried out with a Hallimond tube and Denver flotation cell. The selective flotation of pyrite from arsenopyrite was achieved at around pH 11, employing HTA without using any regulators to depress arsenopyrite.