Flotation and adsorption of a new collector α-Bromodecanoic acid on quartz surface

A new type collector α-Bromodecanoic acid (CH₃(CH₂)₇CHBrCOOH, α-BDA) was synthesized by solvent-free method (Hell–Volhard–Zelinski reaction) in laboratory for the flotation of quartz mineral at a relatively low temperature of 16 °C. The adsorption mechanism of α-BDA collector on quartz mineral surface was established by zeta potential measurements, contact angle measurements, Fourier transform infrared (FT-IR) spectroscopy, and X-ray photoelectron spectroscopy (XPS), in conjunction with the results of quartz micro-flotation tests. The flotation results showed that the activator Ca(II) functioned as an indispensable and crucial factor on the recovery of pure quartz. When the quartz was floated with α-BDA alone at strong alkaline conditions (pH ⩾ 11.50), the recovery rate reached to only 11.9%. However, when using the activator Ca(II) at a concentration of 4 × 10⁻⁴ mol/L, the collector exhibited an excellent performance, where about 99.5% of the quartz had been floated at or above pH value 11.50 at 16 °C. The study revealed that the α-BDA collector had adsorbed on the surface of pure quartz in the forms of electrostatic interaction, hydrogen bonding and chemical adsorption based on the results of zeta potential measurements, contact angle measurements, FT-IR spectra, and XPS.     

Density functional theory study of α-Bromolauric acid adsorption on the α-quartz (1 0 1) surface

Adsorption mechanism of collector α-Bromolauric acid (CH₃(CH₂)₉CHBrCOOH, α-BLA) on α-quartz (1 0 1) surface has been investigated by first-principles calculations based on density functional theory (DFT). The interaction energies of H₂O molecule, calcium ions (Ca²⁺), hydroxyl ions (OH⁻), calcium hydroxyl ions (Ca(OH)⁺), and α-BLA⁻ ions with α-quartz (1 0 1) surface were in the order of Ca(OH)⁺ < Ca²⁺ < OH⁻ < H₂O < α-BLA⁻. The results revealed that the collector α-BLA cannot adsorb on α-quartz (1 0 1) surface due to the hindrance of hydration shell of quartz surface, while Ca(OH)⁺ could repulse the hydration shell and consequently adsorb on quartz surface, which further leads to the adsorption of the collector α-BLA⁻ anions on Ca(OH)⁺-activated quartz surface. Mulliken populations analysis of the external oxygen atom (O2) of quartz surface, calcium atom (Ca) of Ca(OH)⁺, and oxygen atom (O1) of collector α-BLA⁻ (–OH group) shows that the electron transfer between the Ca–O1 and Ca–O2 atoms. The overlap area of electron density between Ca–O1 and Ca–O2 atoms indicates strong interactions among the three atoms of Ca, O1, and O2, suggesting that Ca(OH)⁺ ions act as a bridge between the α-quartz (1 0 1) surface and the α-BLA collector.     

A mixed collector system for phosphate flotation

Flotation has been used in industry for more than a half century as the primary technique for upgrading phosphate. While the flotation of phosphate was inefficient when oleic acid was used alone as a collector, therefore a mixed collector of oleic acid (HOl), linoleic acid (LA) and linolenic acid (LNA) was employed to improve the recovery of phosphate flotation. The batch flotation results showed that the optimal composition of the mixed collector was 54 wt.% HOl, 36 wt.% LA and 10 wt.% LNA. Additionally, the effect of pH on the mixed collector application was studied while considering the surface tension, contact angle and micro-flotation. The results showed that the mixed collector should be used at a pH of 9.5. Above a pH of 9.5, the adsorption of fatty acids dimers on the apatite surface hindered phosphate flotation. The influence of the mixed collector assembly on apatite flotation was also investigated. It was demonstrated that due to its low critical micelle concentration, a sufficiently hydrophobic apatite surface could be generated at a collector concentration of 60 mg/L. In addition, zeta potential experiments suggested that collector adsorption was governed by chemisorption. FTIR and XPS spectra studies further indicated that the chemical reaction involved the carboxyl groups of fatty acids and Ca species at the apatite surface for each fatty acid in the mixed collector.     

Selective flotation of cassiterite with benzohydroxamic acid

The flotation of cassiterite mineral from gangue with a collector benzohydroxamic acid (BHA), and the interactions between the BHA and cassiterite have been investigated. It is shown through microflotation that the BHA is able to flot cassiterite very well, calcite quite limitedly, and quartz not at all, so the selective separation of cassiterite–quartz mixture was readily achieved; while for the efficient separation of cassiterite–calcite mixture containing 48.94% SnO₂, sodium hexametaphosphate (SHMP) was needed as a depressant for the gangue, and under the condition of the BHA 100 mg L⁻¹, SHMP 3.5 mg L⁻¹, a cassiterite concentrate with the grade of 85.50% SnO₂ was obtained with the recovery of SnO₂ 95.5%. Batch flotation further demonstrated that for an industrial tin slime, which contained 0.42% Sn, 13.65% SiO₂, 24.14% CaO, 16.60% MgO, 4.50% Al₂O₃ and 6.58% Fe, the tin recovery of 84.5% after one separation was reached with the concentrate grade of 1.84% Sn under the condition of the BHA 178 mg L⁻¹, SHMP 27 mg L⁻¹. In terms of zeta potential and infrared spectra studies the main interactions between the collector BHA and the mineral cassiterite in a flotation system are chemisorption with the formation of Sn–BHA compounds rather than electrostatic attractions between them.     

Surface characterisation,collector adsorption and flotation response of enargite in a redox potential controlled environment

We previously investigated oxidation of the surface of natural enargite (Cu₃AsS₄) under potentiostatic control and the formation of oxidation species at the mineral surface at selected applied potentials in the oxidative range. Here we further extended the research by incorporating flotation collectors into the system. Electrochemical techniques, X-ray photoelectron spectroscopy (XPS) and microflotation in a redox potential controlled environment were applied to examine surface properties, collector adsorption and flotation response of enargite in pH 10 solutions of sodium ethyl xanthate (SEX) and sodium dialkyl dithiophosphinate (3418A). The spectral details of XPS analysis of electrochemically treated enargite surfaces show significant adsorption of SEX and 3418A collectors onto enargite at an applied voltage of +516 mV, but no adsorption of both collectors at −400 mV. The results of XPS analysis agree with the floatability of enargite determined by microflotation, showing that the flotation recovery was highest at high oxidative potential (+516 mV), then decreased at low oxidative potential (+100 mV) and was very poor at −400 mV. These results confirm that enargite floatability can be efficiently controlled electrochemically.     

Flotation behaviors of ilmenite,titanaugite, and forsterite using sodium oleate as the collector

The flotation behaviors of ilmenite, titanaugite, and forsterite using sodium oleate as the collector were investigated using microflotation experiments, zeta-potential measurements, Fourier transform infrared (FT-IR) analyses, X-ray photoelectron spectroscopy (XPS) analyses and the artificially mixed minerals flotation experiments. The results of the microflotation experiments indicate that ilmenite exhibits good floatability when pH > 4.0. Titanaugite possesses a certain floatability at pH 4.0–6.0 and pH > 10.0, and forsterite possesses certain floatability at pH 5.0–7.0 and pH > 9.0. The results of FT-IR and XPS analyses indicate that sodium oleate mainly interacts with Fe, resulting in ilmenite flotation; that the Ca and Mg on the titanaugite surface chemically reacted with sodium oleate, and that the Mg on the forsterite surface chemically reacted with sodium oleate under acidic condition. However, sodium oleate mainly reacted with the Ca and Mg on the titanaugite surface, whereas sodium oleate mainly reacted with the Mg on the ilmenite and forsterite surfaces under alkaline conditions. The results of the artificially mixed minerals flotation experiment demonstrate that the concentrate of TiO₂ grade increases from 16.92% to 30.19% at pH 5.4, which represents the appropriate conditions for the flotation separation of ilmenite from titanaugite and forsterite under weak acidic conditions.     

Flocculation and flotation response of Rhodococcus erythropolis to pure minerals in hematite ores

Rhodococcus erythropolis as a flotation collector for hematite was evaluated in the study. The surface morphology and cell wall composition of R. erythropolis was analyzed. Zeta potentials for four pure minerals from hematite ores were measured before and after adsorption by R. erythropolis. Pure mineral flotation tests and mixed mineral separation tests were performed to describe adsorption characteristics and mechanisms. A rod-shaped bacterium was detected with CH₂, CH₃ and COO groups on its cell wall that imparted hydrophobicity and negative charges. The ability of R. erythropolis to collect hematite was stronger than its ability to collect quartz, kaolinite and apatite. For a pulp pH of 6 and a cell concentration of 75 mg/L, recovery rate of hematite was 89.67%. The recovery differences between hematite and quartz, kaolinite and apatite were 66.43%, 60.36% and 54.30%, respectively. These data indicated that electrical properties of hematite surface were more suitable for adsorption of R. erythropolis than other three minerals. The adsorbed hematite particles appeared as large agglomerates after interaction with R. erythropolis. The quartz, kaolinite and apatite particles, however, were in the form of dispersed particles or small agglomerates. The chemical adsorption of hematite on bacterial cell wall resulted in agglomeration. The effects of flocculation and flotation of R. erythropolis on micro-fine hematite particles were characterized for the first time. The results showed that R. erythropolis can act as a flotation collector for hematite from hematite ores.     

Aqueous dispersions of nanobubbles: Generation,properties and features

Nanobubbles (NBs) have interesting and peculiar properties such as high stability, longevity and high surface area per volume, leading to important applications in mining-metallurgy and environmental areas. NBs are also of interest in interfacial phenomena studies involving long-range hydrophobic attraction, microfluidics, and adsorption at hydrophobic surfaces. However, little data are available on effective generation of concentrated NBs water dispersions and on their physicochemical and interfacial properties. In this work, air was dissolved into water at pH 7 and different pressures, and a flow was depressurized through a needle valve to generate 150–200 nm (mean diameter) NBs and MBs-microbubbles (about 70 μm). Microphotographs of the NBs were taken only in the presence of blue methylene dye as the contrast medium. Main results showed that a high concentration of NBs (number per volume) was obtained by decreasing the saturation pressure and surface tension. The number of NBs, at 2.5 bar, increased from 1.0 × 10⁸ NB mL⁻¹ at 72.5 mN m⁻¹ to 1.6 × 10⁹ NB mL⁻¹ at 49 mN m⁻¹ (100 mg L⁻¹ α-Terpineol). The NBs mean diameter and concentration only slightly varied within 14 days, which demonstrates the high stability of these highly concentrated NBs aqueous dispersions. Finally, after the NBs were attached to the surface of a grain of pyrite (fairly hydrophobic mineral), the NBs dramatically increased the population of MBs, which shows the enhancement of particle hydrophobicity due to NBs adhesion. The results were explained in terms of interfacial phenomena and it is believed that these tiny bubbles, dispersed in water at high concentrations, will lead to cleaner and more sustainable mineral flotation.     

Modification of ilmenite surface properties by superficial dissolution method

Acid surface dissolution as a pretreatment method converts Fe²⁺ ions on the ilmenite surface to Fe³⁺ ions. XPS analysis showed that the content of Fe³⁺ increases from 48.5% to 59.8% after surface dissolution for 15 min in a solution of sulfuric acid with a concentration of 10%. This conversion, without any phase transformation, decreases the zeta potential of ilmenite in a wide pH range, resulting in a shift in IEP (Iso-Electric Point) from a pH of 5.4 to 2.3. FTIR spectra and zeta potential measurements showed that the increase of oleate ions adsorption on the ilmenite surface, resulting from the surface dissolution process, is insignificant. After surface dissolution, the formation of more ferric iron oleate species (Ksp = 10^−29.7) being more stable than ferrous iron oleate (Ksp = 10^−15.5) compounds yields an increase of ilmenite hydrophobicity and floatability in a wide pH range. Using 3.65 × 10⁻⁴ M sodium oleate at a pH of 6.3, the maximum flotation recoveries are obtained as 73.5% and 92% for non-treated and acid pretreated ilmenite, respectively.     

Adsorption of copper sulphate on PGM-bearing ores and its influence on froth stability and flotation kinetics

Copper sulphate is used as an activator in the flotation of base metal sulphides as it promotes the interaction of collector molecules with mineral surfaces. It has been used as an activator in certain platinum group mineral (PGM) flotation operations in South Africa although the mechanisms by which improvements in flotation performance are achieved are not well understood. Some investigations have suggested these changes in flotation performance are due to changes in the froth phase rather than activation of minerals by true flotation in the pulp zone. In the present study, the effect of copper sulphate on froth stability was investigated on two PGM containing ores, namely Merensky and UG2 (Upper Group 2) ores from the Bushveld Complex of South Africa. Froth stability tests were conducted using a non-overflowing froth stability column. Zeta potential tests and ethylenediaminetetraacetic acid (EDTA) tests were used to confirm the adsorption of reagents onto pure minerals commonly found in the two ores. The results of full-scale UG2 concentrator on/off copper sulphate tests are also presented. The UG2 ore showed a substantial decrease in froth stability in the order of reagent addition: no reagents > copper > xanthate > copper + xanthate, while Merensky ore showed a slight decrease. It was shown through zeta potential measurements that copper species were to be found on plagioclase, chromite, talc and pyrrhotite surfaces and through EDTA extraction that this copper was in the form of almost equal amounts of Cu(OH)₂ and chemically reacted copper ions on the Merensky and UG2 ore surfaces. In certain cases, the presence of copper sulphate and xanthate substantially increased the recovery, and therefore the implied hydrophobicity, of pure minerals in a frothless microflotation device. It was, therefore, proposed that increases in hydrophobicity beyond an optimum contact angle for froth stability, were the cause of instabilities in the froth phase and these were found to impact grade and recovery in a full-scale concentrator. Differences in the extent of froth phase effects between the different ores can be attributed to differences in mineralogy.     

A modification in the flotation process of a calcareous–siliceous phosphorite that might improve the process economics

The amenability of a low-grade Egyptian phosphorite to flotation for separation of both calcareous and siliceous gangue minerals by just pH control was investigated. The ore, assaying 19.39% P₂O₅, 16.1% L.O.I. and 12.41% A.I. is mainly composed of francolite and hydroxy apatite minerals consolidated into three different phosphatic varieties according to texture and origin, i.e. coarse phospho-chem, sharp-edged phospho-clast and fine cementing phospho-mud. This was endorsed by microscopic investigation of thin sections. X-ray diffraction analysis of the ore sample showed that the main gangue minerals are calcite and quartz with minor dolomite and some gypsum.Anionic flotation of calcite, under pH4.5, was successfully conducted on the −0.25 + 0.074 mm phospho-chem fraction without any use of phosphate depressants. This was followed by direct flotation of phosphate after raising the pH to 9. Mechanical cleaning of the phospho-concentrate was carried out, without any addition of the collector to get rid of the entrained silica. About 3 kg/t of oleic acid was required for the whole process which was added step-wise 0.5 kg/t each except for the first step which was 1.0 kg/t to activate the flotation pulp. Phospho-concentrate assaying 30.54% P₂O₅, 8.7% L.O.I. and 5.76% A.I. with a P₂O₅ recovery of 64.34% was finally obtained without the use of expensive depressants, e.g. phosphoric acid or sodium silicate.A trial to explain the results in view of others’ findings and in terms of the ore mineralogical characteristics was shown.     

Flotation of rare earth minerals from silicate–hematite ore using tall oil fatty acid collector

The flotation of rare earth (RE) minerals (i.e. xenotime, monazite-(Nd), RE carbonate mineral) from an ore consisting mainly of silicate minerals (i.e. primary silicate minerals and nontronite clay) and hematite was investigated using tall oil fatty acids (Aero 704, Sylfat FA2) as collector. The RE minerals are enriched with Fe. The effects of tall oil fatty acid dosage, pH, temperature, and conventional depressants (sodium lignin sulfonate, sodium metasilicate, sodium fluoride, sodium metasilicate and sodium fluoride, and soluble starch) were determined at grinding size of P80 = 63 μm. At this grinding size, the grain size of the RE minerals ranges from 2 to 40 μm, percentage liberation is 9–22%, and percentage association with nontronite and quartz is 30–35%. Results indicated that Sylfat FA2 at 22450 g/t concentration was the more efficient tall oil fatty acid collector at natural pH (pH 7) to basic pH (pH 10.0–11.5). Flotation at the room temperature (25 °C) gave higher selectivity than 40 °C temperature flotation. The results on the effect of depressants showed similar selectivity curves against the gangues SiO₂, Al₂O₃, and Fe₂O₃ suggesting that the chemical selectivity of the depressants has been limited by the incomplete liberation of the RE minerals in the feed sample. High recoveries at 76–84% (Y + Nd + Ce)₂O₃ but still low (Y + Nd + Ce)₂O₃ grade at 2.1% in the froth were obtained at flotation conditions of 63 μm, 25 °C, pH 10.5, 1,875 g/ton sodium metasilicate and 525 g/ton sodium fluoride or 250 g/ton soluble starch as depressant for the silicates and hematite, and 22,450 g/t Sylfat FA2 as collector for the RE minerals (initial (Y + Nd + Ce)₂O₃ feed grade = 0.77%). The recoveries of gangue SiO₂, Al₂O₃, and Fe₂O₃ in the froth were low at 25–30%, 30–37%, and 30–36%, respectively. The mineralogical analysis of a high grade froth and its corresponding tailing product showed that the RE minerals have been concentrated in the froth while the primary silicate minerals and hematite have been relatively concentrated in the tailing. However, the clay minerals, primary silicate minerals, and hematite still occupy the bulk content of the froth. This suggests that incomplete liberation of the RE minerals led to the poor grade result, supporting likewise the selectivity curve results by the different depressants. This study showed that liberation is important in achieving selective separation.     

On the nanobubbles interfacial properties and future applications in flotation

Nanobubbles, generations forms, basic studies and applications constitute a growing research area, included their usage in advanced mineral flotation. Yet, there are investigation needs for sustainable generation procedures, stability and understanding the nanobubbles interfacial properties and structures. Results proved that a reduction in pressure makes the super-saturated liquid suffers cavitation and nanobubbles were generated. Medium pH and solutions tested were adjusted, in the air saturation vessel, before the nanobubbles were formed, and this allowed to control (in situ) the surface charge/zeta potential-size of the forming nanobubbles. Measurements obtained with a ZetaSizer Nano equipment showed zeta potential values, in the presence of 10⁻² mol L⁻¹ NaCl, displaying sigmoidal pH behaviour between pH 2 (+26 mV) and 8.5 (−28 mV); an isoelectric point was attained at pH 4.5 and were positively charged (up to 23 mV) in acidic medium, a phenomenon which has not been previously observed. In alkaline medium, bubbles were highly negative zeta potential (−59 mV) at pH 10. The double layers appear to play a role in the formation of stable nanobubbles providing a repulsive force, which prevents inter-bubble aggregation and coalescence. Accordingly, the sizes of the nanobubbles depended on their charge and increased with pH, reaching a maximum (720 nm) around the isoelectric point (±5 mV). Highly charged and small nanobubbles (approximately 150–180 nm) were obtained in the presence of surfactants (10⁻⁴ mol L⁻¹ of alkyl methyl ether monoamine or sodium dodecyl sulphate); the zeta potential values in these experiments followed a similar trend of other reported values, validating the technique used with the nanobubbles sizes varying with pH from 150 to 400 nm. Thus, charged and uncharged stable nanobubbles can be tailor-made with or without surfactants and it is expected that their use will broaden options in mineral flotation especially if collectors coated nanobubbles (“bubble-collectors”) were employed. A detailed and updated review on factors involving stability, longevity and coalescence of nanobubbles was made. It is believed that future trend will be on sustainable formation and application of nanobubbles at industrial scale contributing to widen applied research in mineral, materials processing and liquid effluent treatment by advanced flotation.     

Separation of amine-insoluble species by flotation with nano and microbubbles

Amines (alkylamines–ether amines) are employed on a large scale to separate iron ores by reverse flotation of the gangue particles (mostly quartz and silicates). Quartz gangue particles coated with amine collector are dumped in tailings dams as concentrated pulps. Then, the fraction of the amines that detach from the surfaces and the portion that is soluble in water, contaminate surface and ground-water supplies. This work presents a novel flotation technique to remove decyl-trimethyl-ether-amine (collector employed in Brazilian iron mines) from water. This amine forms precipitates at pH > 10.5 which are removed by flotation with microbubbles (MBs: 30–100 μm) and nanobubbles (NBs: 150–800 nm). Bubbles were generated simultaneously by depressurization of air-saturated water (P_sat of 66.1 psi during 25 min) forced through a flow constrictor (needle valve). The flotation by these bubbles is known as DAF-dissolved air flotation, one of the most efficient separation technologies in water and wastewater treatment. Herein, best results (80% amine removal) were obtained only after selective separation of the MBs from the NBs exploring the fact that while the NBs remain dispersed in water, the MBs rise leaving the system. The MBs, because of their buoyancy, rise too rapidly and do not collide and adhere appropriately at the amine colloids/water interface, even causing some precipitates breakage. It was found that the “isolated” NBs attach onto the amine precipitates; aggregate (flocculate) them and entrain inside the flocs before rising by flotation. Because of the low residual amine concentration in water (6 mg L⁻¹), it is believed that this flotation technique have potential in this particular treatment of residual amine-bearing effluents.     

Interaction mechanism of miscible DDA–Kerosene and fine quartz and its effect on the reverse flotation of magnetic separation concentrate

In this study, a modification of oil assisted flotation processes of quartz particles has been proposed, which is based on introduction of miscible Dodecylamine (DDA)-Kerosene as collector with DDA cationic surfactant coated on kerosene to the hydrophilic quartz particles in the pulp. The property of miscible DDA–Kerosene emulsion was investigated. Due to the adsorption of DDA at kerosene/water interface, a smaller and uniform kerosene emulsion formed. Addition of cationic surfactant to the kerosene emulsion changed the zeta potential value from negative to positive, which resulted in enhancing the adhesion of the oil droplets to negatively charged quartz. The results showed that agglomeration and flotation process can be realized simultaneously with DDA–Kerosene. The agglomeration of fine quartz minerals in the presence of miscible DDA–Kerosene led to the formation of very large compact agglomerates resulting in increasing hydrophobicity of the particles and inducing a higher probability of collision and adhesion to air bubble. Experimental data indicated that miscible DDA–Kerosene had better selectivity and stronger collectability to quartz than DDA–HCl, which can be used as an efficient collector in the reverse flotation of magnetic separation concentrate of TISCO. At the same DDA dosage (60 g/t), separation efficiency got to 18.53% when using DDA–HCl as collector; while a better result was obtained with DDA–Kerosene, the efficiency of separation reached 59.07% which was identical with 120 g/t DDA–HCl.     

The removal of zinc from liquid streams by electroflotation

The removal of heavy metals from dilute aqueous solutions (in the range of 10⁻⁷–10⁻⁴ mol dm⁻³) is often not acceptable using classical methods, which do not achieve levels in accordance with environmental quality standards. Electroflotation has certain desirable characteristics, compared to dissolved and dispersed air flotation, particularly in regard to the small bubble size distribution of the process. The aim of this work was to develop an electroflotation (EF)/electrocoagulation (EC) cell to study this combined process and the influence of some relevant parameters/variables, such as collector concentration, tension and current density variation, on the removal of zinc from synthetic solutions containing 20 mg l⁻¹ of the metal. A platinum gore (5 mm) anode and stainless steel mesh cathode were used in the electroflotation cell. The work showed that it was possible to remove zinc by electroflotation, 96% removal being achieved using sodium dodecyl sulfate (SDS) as collector in the stoichiometric ratio 1:3, current density of around 8 mA/cm² and an inlet pH of about 7.0.     

Metal ions released from fluid inclusions of quartz associated with sulfides

The release of fluid inclusions has a strong potential for the unintentional activation of minerals during flotation. The present study aims to characterize fluid inclusions in natural quartz from a complex sulfide ore deposit. The results indicate that many fluid inclusions exist in the quartz. Under the experimental conditions of 2 g of quartz cleaned in 40 ml of pure deionized water under an inert atmosphere, the concentrations of Cu, Pb, Zn and Fe in aqueous solution reach concentrations of 1.92 × 10⁻⁷, 8.88 × 10⁻⁷, 8.31 × 10⁻⁷ and 90.33 × 10⁻⁷ mol/L, respectively. These values are significantly greater than those from the experimental non-oxidative dissolution of the quartz. In addition, the concentrations of metal ion released from fluid inclusions in the quartz sample at conditions approached “typical” industrial flotation environment are determined. The results indicate that the fluid inclusions of quartz represent the considerable sources of Cu, Pb, Zn and Fe in the aqueous solution. The present investigation provides a new understanding for the source of the unavoidable metal ions in the flotation pulp and may benefit understanding of the flotation theory.     

Froth flotation of sphalerite: Collector concentration,gas dispersion and particle size effects

This experimental work on sphalerite flotation investigated the effect on flotation performance of three particle size fractions, namely, coarse (d₈₀ = 100 μm), medium (d₈₀ = 39 μm) and fine (d₈₀ = 15 μm), bubble size distribution, superficial air velocity, and collector dosage. Bubble size distributions were characterized with the image analysis technique. The two-phase (liquid–gas) centrifugal pump and frother addition (MIBC, 5–30 ppm) allowed generating bubble diameters between 150 and 1050 μm, and air holdup ranging from 0.2% and 1.3%. Main results showed that each particle-size distribution required an optimal bubble-size profile, and that sphalerite recovery proceeded from mechanisms involving true flotation (when J_g = 0.04 cm/s and 1.9 × 10⁻⁴ M SIPX). However, cluster-flotation occurs at high collector dosage (when J_g = 0.04 cm/s and d₃₂ between 285 and 1030 μm), and requiring further investigation.     

The effect of an external magnetic field on cationic flotation of quartz from magnetite

In this study, the effect of an external magnetic field on cationic flotation of quartz from magnetite was investigated by using a magnetic micro-flotation column. For this purpose, a micro-flotation column jacketed with three coils was fabricated to create a funnel-shaped magnetic field. Both the theoretical magnetic field strengths and the magnetic forces were calculated. The results from flotation experiments with 6 × 10^?5 M dodecylamine as collector using a binary mixture of quartz and magnetite as a feed material show that the separation efficiency increased from 0% without the magnetic field to 88% in the presence of the magnetic field. The significant enhancement in separation efficiency is evident.     

Post-regrind selective depression of pyrite in pyritic copper–gold flotation using aeration and diethylenetriamine

The present study investigates the effect of aeration and diethylenetriamine (DETA) on the selective depression of pyrite in a porphyry copper–gold ore, after regrinding (at grind sizes, d₈₀ = 38 and 8 μm) with respect to Au recovery and grade using oxygen demand tests, flotation, QEMSCAN, X-ray spectroscopy (XPS) and EDTA extraction analysis. It was found that pyrite depression increases after aeration and with decreasing grind size. This was observed to be due to the markedly higher oxygen consumption rate of pyrite at the 8 μm (kla = 0.10 min⁻¹) than at the 38 μm grind size (kla = 0.02 min⁻¹). The addition of DETA improved pyrite depression (9% with aeration only versus 39% with aeration + DETA) at the 38 μm grind size. Gold and copper flotation recovery followed pyrite recovery for the two grind sizes using XD5002 in the presence of air and DETA.The surface analysis (XPS and EDTA extraction) revealed that the significant pyrite depression at the 8 μm grind size was due to increased amount of surface iron oxides, oxy-hydroxides (FeO/OH), sulphate species and increased liberation of mineral phases (QEMSCAN analysis), whilst the poorer pyrite depression at the 38 μm grind size was due to insufficient liberation of mineral phases and the persistence of activating Cu on the pyrite surface. The addition of DETA increased pyrite depression at the coarser grind size due to a significant reduction in Cu(I)S and increased Cu(II)O species, correlating with the flotation results of pyrite under this test condition. Two-stage copper and pyrite flotation, followed by Au cleaning after regrinding to 38 μm grind size, under high pH or aerated condition is proposed as the recommended route to optimise Au flotation.