Hallimond Tube Research Articles

Electrochemical Performance of Ti Gr. 2 as Electrodes in Contact with Saline Suspension of Clays during the Electroflotation Process

The presence of clays in copper minerals has a significant negative impact during their processing, leading to low recoveries during the flotation process. In saline environments, the presence of these clays promotes operational problems associated with salinity, leading to decreases in the copper concentrate grade, alterations in the rheology of the mineral pulp, reduction in the selectivity of copper during the flotation process, declines in the quality of clarified water, and excessive corrosion of metallic components. This study explores the electroflotation of kaolinite and montmorillonite clays in NaCl solutions using a modified Hallimond tube coupled with Ti Gr. 2 electrodes for bubble generation via water electrolysis and the corrosion analysis of these electrodes applying the superposition model. The electroflotation results show recovery of clays close to 72.68% for kaolinite, 88.44% for montmorillonite, and 67.36% for a mixture of both clays. The presence of clays helps reduce the corrosive effects of Ti Gr. 2 from 0.069 A/m2 in NaCl to 0.0073 A/m2 in NaCl with montmorillonite clay.

A new insight into the mechanism of MNB-assisted flotation of copper: A link between chalcopyrite and its-bearing bulk ore

The present study systematically explores the relationship between chalcopyrite mono-mineral and copper-bearing ore flotation in the presence and absence of micro- and nano-bubbles (MNBs). Ultrafine bubbles were generated through a cavitation mechanism, and their stability, size, and zeta potential were monitored over a period of 0–25 days. Micro-flotation and batch rougher kinetic flotation experiments were carried out with and without ultrafine bubbles using a modified Hallimond tube and 2.5 L Denver® flotation cell, respectively. The results showed that the presence of MNBs improved the recovery of chalcopyrite mono-mineral and its ore by 24.5 % and 7 %, respectively. Furthermore, the adsorption behavior of sodium isopropyl xanthate (SIPX) collector at various concentrations was analyzed in the presence and absence of stable MNBs using UV–visible spectroscopy, FTIR analysis and kinetic models. The adsorption studies supported the micro-flotation findings, demonstrating that the presence of MNBs not only boosted collector adsorption on the chalcopyrite surface (by an average of 73.8 %) but also improved the adsorption kinetics (by 69.44 %). The sorption kinetics followed the pseudo 2nd order model in the presence of MNBs, while in the absence of MNBs, both pseudo 1st order and pseudo 2nd order models were observed. The sorption of SIPX onto chalcopyrite was identified as a chemisorption process in the presence of MNBs, whereas it was a physicochemical sorption in the absence of MNBs.

Халлимонд түтігіндегі мыс сульфидті минералдардың флотациясы

Under laboratory conditions, studies were carried out to determine the hydrophobicity of the surface of copper sulfide minerals bornite and chalcopyrite by differential thermal analysis and the infrared (IR) spectra of samples of these minerals were studied before and after the experiments. From the nature of the absorption of copper sulfide minerals by IR radiation, it is possible to determine the best indicators of the adsorption of reagents on the surface of minerals. When treating the chalcopyrite surface with anabazinium-O, O-dimethylthiophosphate and N-phenylthiosemicarbazide reagents N-morpholinylacetic acid has been found to weaken hydrogen bonds and evaporate adsorbed moisture. This indicates an increase in the hydrophobicity of the chalcopyrite surface compared to bornite. Studies of the non-soil flotation of the monomineral fraction of sulfide minerals were carried out in the Hallimond tube. During flotation of chalcopyrite treated with a solution of 1% N-phenylthiosemicarbazide of N-morpholinyl acetic acid, its extraction was 94.54%. The achieved indicators are confirmed by the results of differential thermal analysis and IR spectroscopy

Insight into the influence of surface wettability on flotation properties of solid particles – Critical contact angle in flotation

Bubble-particle attachment is a fundamental element of the flotation process, and its occurrence depends on the stability of the thin liquid film separating these objects. In this study, the effect of surface wettability on the stability of liquid film and subsequent attachment was investigated by flotation of glass microspheres (70–110 μm) with controlled contact angles (9–89°) in a Hallimond tube. Additionally, pH was varied to determine the electrostatic interactions between the bubble and particles. The results showed that for the flotation process to take place, the minimum (critical) value of the contact angle must be exceeded. This value was found to be ca. 25° when the electrostatic interactions were either attractive or weakly repulsive and as high as 62° for strong repulsive electrostatic interactions. These findings highlight the role of attractive hydrophobic interactions, whose importance increases with increasing surface contact angle in the context of stability of thin liquid films.

Collector mixtures and their synergistic effect on quartz floatability

Sinergy is the interaction of two or more agents to produce a combined effect greater than the sum of their separate effects. Etherdiamine yields superior results for quartz floatability in a Hallimond tube and higher selectivity in the reverse bench scale cationic flotation of an iron ore, when compared to ethermonoamine. Blending these collectors yields better results than each one used individually characterizing a synergistic effect. This work evaluated the effects of the collectors ethermonoamine, etherdiamine and the mixture of these at the ratio 1:1 on the flotation of the quartz through the microflotation and bench flotation tests with a typical Brazilian iron ore. The results demonstrated the occurrence of synergistic effects in tests performed at concentrations of 1 and 3 mg/L and pH 10.5, in the absence of a depressant. In the presence of a depressant, the synergy was not observed under the same tested conditions, due to the collector-depressant interaction. On other hand, the bench flotation tests indicated the occurrence of synergy regarding silica content in the concentrate while an additive effect was observed for the iron recovery and Selectivity Index index demonstrating that a feasibility of using collector mixtures in this process, was not clearly achieved on the tested ratio 1:1.

Aqueous bifunctionalization of cellulose nanocrystals through amino and alkyl silylation: functionalization, characterization, and performance of nanocrystals in quartz microflotation

Surface modifications of cellulose nanomaterials can be used to tailor their surface charge and hydrophilicity-hydrophobicity characteristics. Additionally, it can facilitate the selective interaction of nanocelluloses with other solid particles to further expand their applicability in different fields. For instance, cellulose nanocrystals (CNC) with amphiphilic features are potential green alternatives in mineral processing such as particle flotation. In the present study, aqueous, one- and two-step silylation of CNCs with amino and alkyl silanes was considered to create a novel bifunctionalized CNCs that contained both positively charged amino silane moieties and hydrophobic alkyl chains. Especially, the effects of reaction conditions and different reaction routes on the silylation were investigated, and the electric surface potential and hydrophobicity of CNCs were determined. The bifunctionalization conducted by the simultaneous addition of an amino silane and alkyl silane led to a high reaction efficiency, and the grafting amount was notably higher than that obtained with the sequential reactions with individual reagents. After the functionalization, the hydrophobicity of the CNCs was strongly altered, leading to water contact angles of up to 135° on CNC films. However, the silylation with amino silanes slightly affected the ζ-potential of the functionalized CNCs. Due to the relatively low ζ-potential, the interaction and orthokinetic attachment of CNCs onto quartz surfaces were insufficient, resulting in a limited flotation recovery in microflotation using a Hallimond tube.

Floatability and calculated reactivity of sulfide minerals and gold

The paper provides the results of theoretical reactivity calculations for gold, molybdenum, stibnite, galena, chalcopyrite, arsenopyrite and pyrite in comparison with such experimental data as the floatability of monomineral fractions with butyl xanthate, wetting angle values, changes in the kinetics of the mineral electrode potential. The following calculation series in terms of reactivity and oxidizing ability were established by calculation: Au < Sb2S3 < MoS2 < PbS < CuFeS2 < FeAsS < FeS2. During the Hallimond tube flotation, natural gold grains demonstrated the highest recovery (70 %) in the рН = 5÷7 range compared to all the studied sulfides. Molybdenite and stibnite are floated at the level of 50 % under the same conditions. As pH increases towards the alkaline region, a decrease in the floatability of all sulfides except for chalcopyrite is observed. It was established that the highest recovery is achieved when the required time of conditioning with the collector is the inverse of their reactivity. The measured wetting angle of a drop of water on an untreated surface has the highest value (78°) for a gold plate, and the lowest one (67°) for pyrite, but the latter features the greatest increase in the wetting angle (by 15°) after treatment with butyl xanthate at a concentration of 10–4 mol/l and pH = 6. For molybdenite, treatment with butyl xanthate has practically no effect on the measured wetting angle. The Sb2S3 < PbS < CuFeS2 < FeAsS < FeS2 series is determined according to the electrode potential in the рН = 2.0÷5.6 range. Theoretical calculations and experimental data obtained when studying monofractions of sulfides and gold showed that experimental conditions (pH, conditioning time, collector concentration) significantly affect the floatability. The calculated reactivity of chemical sulfide compounds and gold in comparison with experimental results proved the importance of maintaining certain flotation conditions to create contrast in the floatability of minerals.

A theoretical and experimental study of the effects of NaCl and the competitive chemisorption of ions at the surface sites in the context of galena flotation

• The recovery of galena by collector-less flotation improves as a result of NaCl addition. • Our galena surface complexation model is a “two-site / not amphoteric” model. • The theoretical predictions of the models support the experimental results. • The decreasing repulsion at higher ionic strengths corresponds to a higher galena recovery. In this study we have investigated the effects of increasing the NaCl concentration on the flotation of galena. Experiments were carried out using a Hallimond tube in NaCl solutions with concentrations of 1, 10 and 100 mM, at pH 9. It was found that the recovery of galena by collector-less flotation improved for higher NaCl concentrations. Zeta potential measurements made on galena particles conditioned in NaCl solutions were used to calibrate the parameters for describing a chemisorption model representing charge regulation at the galena binding sites. Our galena chemisorption model presented here is a “two-site/not amphoteric” surface complexation model. A chemisorption model representing the charge regulation process on the surface of an air bubble has also been applied. The zeta potentials calculated using these models were in agreement with the measured values, indicating that these models can be applied to predict the potentials on the surface of galena and an air bubble for a range of NaCl concentrations and pH. To investigate the mechanisms of particle-bubble interactions for each NaCl concentration, the total interaction free energy as a function of the separation distance between galena and an air bubble was determined. It was found that at a NaCl concentration of 1 mM, due to adsorption of ions at the galena surface, repulsion dominated the interaction, and the lowest galena recovery was reported. With an increase in NaCl concentration in solution to 100 mM, the total interaction between galena and an air bubble was represented by a purely attractive total interaction free energy curve. The theoretical predictions of the models supported the experimental results, with a stronger attraction predicted by the models at higher ionic concentrations, corresponding to a higher galena recovery during flotation.

Influence of surface dissolution on reagents’ adsorption on low-grade phosphate ore and its flotation selectivity

A preliminary study was conducted on the Hallimond tube to find routes for the direct flotation of fluorapatite. Carboxymethylcellulose-sodium oleate and sodium alginate-sodium oleate were the most promising depressant-collector combinations. Apatite recovery exceeded 95%. Conversely, replication of these findings in the mechanical flotation cell proved to be different. The results show a flotation of the calcite, while the fluorapatite remains in the tailings. Grades of 27.63% P2O5 with a recovery of 69.9% and 28.22% P2O5 with a recovery of 73.93% were obtained in the non-floated fraction using 1500 g/t of sodium oleate and 25 g/t of sodium alginate and carboxymethylcellulose as depressants, respectively.The effects of metal ions on the flotation behavior of fluorapatite, calcite, and quartz were investigated through micro-flotation tests and bench-scale flotation experiments. The findings were further elucidated by dissolution study, zeta potential measurements, and FTIR analyses. The results demonstrated that pulp water containing large amounts of Ca2+, Mg2+, and Fe3+ directly influences the performance of apatite flotation. Fluorapatite recovery substantially dropped from 97.27% in deionized water, reaching values below 11.11% at alkaline pH. These ionic species interfere in the interfacial processes and perturb selective adsorption. Ca2+ ions favor the precipitation of CaCO3, hence forms a coating on the apatite surface, rendering it unavailable for NaOL chemisorption. Ca2+, Mg2+, and Fe3+ complex with the reagents and the precipitates adsorb onto the minerals’ surfaces, impairing their floatability. Also, their presence activates the quartz surface, increasing its recovery. Zeta potential curves overlap, implying a similar build-up of negative charge on the three mineral surfaces. The most intense peaks in FTIR spectra indicated more adsorption, suggesting that the detrimental species Ca2+, Mg2+, Fe3+ must be involved in adsorption mechanisms and explain flotation trend change.

New insights related to the flotation of covellite in porphyry ores

Covellite usually occurs accompanying other copper minerals, like chalcopyrite and chalcocite, but there are few studies on covellite flotation. The effect of collectors O-isopropyl-N-ethyl thionocarbamate (IPETC) and potassium amyl xanthate (PAX) and pH on covellite and pyrite flotation was investigated through a Hallimond tube test using pure covellite and pyrite and a Denver cell test using porphyry ore. Pure covellite and pyrite were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR). Moreover, the covellite was characterized using scanning electron microscopy coupled to energy dispersive spectroscopy (SEM-EDS). Porphyry ore was characterized by automated mineralogy using scanning electron microscopy (QEMSCAN®). Design of experiments was utilized to identify the factors with a statistical influence (ANOVA) and obtain the optimal flotation conditions using response surface methodology (RSM) and desirability function. ANOVA test demonstrated that the factors that influence covellite behavior are the collector type and dosage. The results obtained on pure minerals shows that with a high PAX concentration and low pH, it is possible to carry out bulk flotation with recoveries of 93% covellite and 90 % pyrite, and with a low IPETC dosage and high pH, it is possible to get a selective flotation with around 81% covellite and 20% pyrite recoveries. These results were determined using RSM and desirability function, and corroborated with the Hallimond tube test. Then, the flotation results of mixture covellite-pyrite show that selective flotation is feasible with IPETC at alkaline pH with a low dosage displaying recoveries of 97 % covellite and 53 % pyrite. Also, bulk flotation is feasible with PAX at a pH of 8 and a high collector concentration with recoveries of 96% covellite and 88% pyrite. The results show that covellite recovery is not pH-dependent. The Denver cell test with a porphyry ore shows a selective flotation with IPETC at a pH of 11 with a low collector dosage (5 g/ton), achieving recoveries of 92% covellite and 39% pyrite. Also, recoveries of 85% covellite and 75% pyrite were observed for a bulk flotation with IPETC at pH = 8 at the same collector dosage. Therefore, the IPETC can be used as a selective or bulk collector when varying the pH and collector concentration. These results demonstrate that covellite flotation performances remain constant over a wide range of pH values, which allows a selective separation from other sulfides such as pyrite.

Biodepression of Copper-Activated Pyrite with Acidithiobacillus ferrooxidans in Flotation with Fresh and Seawater

Acidithiobacillus ferrooxidans has been shown to be a good depressant of pyrite in freshwater and seawater flotation. However, the effect of these bacteria over copper-activated pyrite has not been studied. At the industrial scale, the activation of pyrite with copper is a common process that occurs because Cu2+ ions, released from other minerals, react with pyrite. This is a problem because Cu2+ ions facilitate the reaction of pyrite with the xanthate collectors, becoming hydrophobic and reaching the froth. In this study, microflotation experiments in a Hallimond tube were conducted to evaluate the depressant effect of A. ferrooxidans over non-activated and Cu-activated pyrite in freshwater and seawater flotation. The experiments were carried out at pH 4, 6, 8, 10 and 12 and pyrite was mixed with CuSO4 at 2.5×10−5 and 5×10−5 M in order to activate its surface. Considering the results obtained in the microflotation tests, it is possible to conclude that Acidithiobacillus ferrooxidans is able to depress non-activated and Cu-activated pyrite at the entire pH range studied (4–12) in freshwater. On the other hand, the use of bacteria in flotation with seawater proved to be effective to depress non-activated and Cu-activated pyrite at pH 8 and 10 with better results achieved at pH 10. At this pH, the non-activated pyrite recovery dropped from 96% to 15%, and the recovery of Cu-activated pyrite dropped from 95% to 32% when the activation was carried out at 2.5×10−5 M, and from 87% to 50% when the activation was conducted at 5×10−5 M of CuSO4. The XPS analysis showed that chalcopyrite and copper (II) hydroxide were formed on the pyrite surface when it is contacted with CuSO4.

Fundamental bioflotation aspects of hematite using an extracted Rhodococcus opacus by-product

The aim of this study is to assess the floatability of hematite using a crude biosurfactant (BS) extracted from Rhodococcus opacus. Throughout high-pressure ethanol extraction, unrefined surfactant was extracted from the bacteria with a yield of 0.3 g/L. An FTIR analysis on this extract, shows the presence of alcohol (–OH) and ketone (C=O) groups, as well as saturated and unsaturated carbon chains, which might originate from mycolates and trehalolipids moieties reported in literature. In addition, FTIR analysis on the modified mineral surface with the unrefined surfactant, confirms a strong interaction between hematite and the crude biosurfactant, showing similar vibrational peaks regarding the hydroxyl and carboxylate groups at 1631 and 3436 cm-1, respectively. Biosurfactant interaction with the mineral particles shifted the isoelectric point from 7.5 to 3.2, turning the hematite more hydrophobic in acidic environments. Surface tension measurements indicate that the unrefined surfactant is slightly more effective, decreasing the surface tension of water compared to the bacteria itself, with a variation of 4 mM/m. Finally, throughout microflotation tests in a Hallimond tube, it is shown that the surfactant doubles bacteria recovery efficiency, reaching a maximum recovery of around 95 % in acidic conditions, which is consistent with electrophoretic studies. The statistical models adjust well the experimental data, achieving R2 values of 93.6 and 91.1% for the hematite flotation using the biomass and the biosurfactant, respectively.

Influence of Terpenic Oil on Flotation Behavior of Sphalerite and Implication for the Selective Separation

Terpenic oil (TO) is commonly used as a flotation frother for the selective separation of sulfide minerals. As a frother, most reports have mainly focused on its effect on froth stability and froth entrainment, whereas its influence on the floatability of sulfide minerals has received little attention. In this work, the influence of TO on the flotation behavior of sphalerite was investigated by using microflotation tests, contact angle and zeta potential measurements, and FT-IR and SEM-EDS analyses. Microflotation tests conducted in a modified Hallimond tube indicated that compared with the collector potassium butyl xanthate (KBX), the flotation recovery of sphalerite was significantly increased when TO was added to the pulp, but the recovery of Cu-activated sphalerite with the addition of TO was lower than that with the addition of KBX. Contact angle measurements demonstrated that the contact angle of sphalerite was distinctly increased by the addition of TO, but the contact angle of sphalerite treated with TO was lower than that treated with KBX after Cu activation. Zeta potential measurements demonstrated that the zeta potential of sphalerite particles was slightly decreased when treated with TO, and the isoelectric point (IEP) was decreased from 3.3 to 3.1 due to the interaction of TO with sphalerite particles. FT-IR and SEM-EDS confirmed that TO could be adsorbed on the sphalerite surface on the formation of the oil film due to its low solubility, thereby increasing the surface hydrophobicity of the sphalerite. In addition, the TO absorbed on the surface acts as a bridging role and promotes the hydrophobic agglomeration of sphalerite particles. These results suggest that except for froth entrainment, the influence of TO on the flotation behavior of sphalerite may be another reason for the misreporting of sphalerite in concentrates.

Testing of New Collectors for Concentration of Fluorite by Flotation in Pneumatic (Modified Hallimond Tube) and Mechanical Cells

In this study, two new collectors for fluorite flotation DP-OMC-1033 (DP-I) and DP-OMC-1234 (DP-II) were tested and compared with oleic acid (OA), sodium oleate (SO) and potassium oleate (PO). According to fluorite grade and fluorite metallurgical recovery, the effect of each collector was determined, both in mechanical and pneumatic cell flotation. The effect of temperature on the collectors from 25 to 55 °C was studied. Flotation tests showed that the best results in terms of fluorite metallurgical recovery were 82.8% and 87.9% for new collectors DP-I and DP-II respectively, for a dosage of 100 g/t and using pneumatic cell. Additionally, in terms of fluorite grade, DP-I showed the best results, achieving 79.7% of CaF2 in roughing step for a dosage of 100 g/t. Fluorite metallurgical recovery and grade in concentrate increased for OA, SO and PO with increasing temperature. However temperature did not have a significant effect on both metallurgy recovery and CaF2 grade using DP-I and DP-II, so the process can be effective at 25 °C reducing operating costs.

A Study of Temperature Effect on the Xanthate’s Performance during Chalcopyrite Flotation

A multi-scale investigation was conducted to study the surface properties of xanthate-absorbed chalcopyrite at elevated temperature to understand the temperature effect on the xanthate’s performance during chalcopyrite flotation. Firstly, a macro-scale study was initiated to investigate the temperature effect on the hydrophobicity of mineral surface by means of contact angle measurement, Hallimond tube microflotation and lab flotation tests; secondly, a micro–scale study was conducted to clarify the temperature effect on the adsorption of chemicals on mineral surface employing an atomic force microscope (AFM) and Fourier transform infrared spectroscopy-attenuated total reflectance (FTIR-ATR). In the experiments, pure chalcopyrite samples were used for contact angle measurement, Hallimond tube microflotation, AFM and FTIR; and copper ore samples (1.51% Cu, 5.88% Fe 0.029% Mo, 5.23% S in weight percentage) were used for lab flotation tests. FTIR spectra and AFM images showed that, when potassium amyl xanthate (PAX) was used as the collector in this study, oily dixanthogen was the main hydrophobic species on the chalcopyrite surface. The morphological change of dixanthogen patches at elevated temperatures has a more significant impact than changes in the amount of adsorption species. Increasing temperature within a certain range is beneficial for the collector’s performance by increasing flotation recovery.

New Insights into the Pre-Concentration of Alunite from a Siliceous ore using Froth Flotation

Alunite is the main non-bauxite source of aluminum. Due to the low Degrees Of Freedom (DOF) of alunite, froth flotation, as a pre-concentration method, is a viable alternative to increase selectivity in downstream processes. The current study was aimed at investigating the pre-concentration of alunite using micro-flotation. In the first step, an optical microscope studies were done to determine DOF of alunite. In the next step, flotation tests were designed. The experiments were performed based on the surface charge differential between alunite and quartz using direct and reverse flotation. In the reverse flotation, Ca+2 and Ba+2 were used to activate the quartz surface. Anionic collector was used to float the gangue minerals. The highest grade and recovery using reverse flotation were 34.96 and 81.33%, respectively. In the direct flotation, the surface of alunite was activated using Ba2+, Ca2+ and F-. The optimum condition was achieved using F- as an alunite activator for particles ranged -37+25 µm with the grade of 31.47%. The grade and recovery were 50 and 89%, respectively. All experiments were conducted in Hallimond Tube. During the experiments, several parameters were controlled.

Aspectos fundamentales de la flotación de hematita usando biosurfactante

Aspectos fundamentales de la flotación de hematita usando biosurfactante Carlos Alberto Castañeda Olivera Departamento de Ingeniería Química y de Materiales, Pontificia Universidad Católica de Rio de Janeiro, Rua Marquês de São Vicente, 225 – Gávea - Rio de Janeiro – CEP: 22453-900, Brasil Recibido 3 de agosto. Revisado 8 de diciembre. Aprobado 17 de diciembre 2019. DOI: https://doi.org/10.33017/RevECIPeru2019.0008/ Resumen El uso de biosurfactantes como reactivos de flotación representa un gran potencial tecnológico y aceptabilidad ambiental en la industria mineral. Siendo así, esta investigación estudia los aspectos fundamentales de la flotación de hematita utilizando el biosurfactante (BS) producido por Rhodococcus erythropolis. El BS fue caracterizado por análisis de bioquímica y mediciones de tensión superficial, mientras que la interacción hematita-BS fue verificada a través de mediciones de potencial zeta, medidas de ángulo de contacto, experimentos de adsorción y espectros FTIR. Los testes de microflotación fueron realizados en tubo de Hallimond modificado y el máximo valor de flotabilidad (99,87%) fue encontrado en pH 3 con una concentración de BS de 100 mg/L para un tiempo de flotación de 1 min. Los datos de la flotabilidad de hematita fueron analizados por regresión polinómica para obtener una función representativa de la microflotación, así como también sus respectivas superficies de respuesta. Finalmente, los resultados mostraron que o biosurfactante producido por Rhodococcus erythropolis puede actuar como un bioreactivo colector en la flotación de hematita. Descriptores: biosurfactante, flotación, hematita, Rhodococcus erythropolis. Abstract The use of biosurfactants as flotation reagents represents a great technological potential and environmental acceptability in the mineral industry. Thus, this research studies the fundamental aspects of hematite flotation using the biosurfactant (BS) produced by Rhodococcus erythropolis. The BS was characterized by biochemical analysis and surface tension measurements, while the hematite-BS interaction was verified through measurements of zeta potential, contact angle measurements, adsorption experiments and FTIR spectra. The microflotation tests were performed in modified Hallimond tube and the maximum floatability value (99.87%) was found in pH 3 with a BS concentration of 100 mg/L for a flotation time of 1 min. The hematite floatability data were analyzed by polynomial regression to obtain a representative function of the microflotation, as well as their respective response surfaces. Finally, the results showed that the biosurfactant produced by Rhodococcus erythropolis can act as a collector bioreagent in the hematite flotation. Keywords: biosurfactant, flotation, hematite, Rhodococcus erythropolis.

An Increase in Process Characteristics of Flotation of Low-Grade Fine-Disseminated Scheelite Ores

The results of investigations into increasing the contrast of process properties of calcite and scheelite due to the combined application of water glass with salts such as sulfates of aluminum, zinc, iron, magnesium; mixtures of water glass and calcium chloride; sodium carboxymethyl cellulose (CMC); combinations of sodium oleate with low-polar compounds (neonol and fatty iso-alcohols); and data on the ultrasonic treatment of the liquid phase and oleate are described. The lowest recovery of calcite during the flotation of a monomineral calcite fraction in the Hallimond tube is attained when jointly using salts of iron(II) and water glass (3(4) : 1). The joint application of water glass and CaCl2 during the flotation of the low-grade scheelite ore with a high carbonate modulus using tap water lowers the calcite flotability. When using recycled water, adding calcium chloride to water glass leads to a certain increase in the yield of the rough concentrate (from 13.8 to 14.1%) with a significant decrease in the recovery of WO3 into the final selection concentrate of scheelite (from 72.7 to 53.3%) and worsens the concentrate quality. The replacement of water glass by CMC showed no satisfactory results. The ultrasonic treatment of the pulp, liquid phase, and collector leads to a certain increase in calcite flotation activity, possibly due to an increase in the liquid phase temperature and in the fraction of the ionic form of oleate. The use of neonols in the reagent flotation mode of the scheelite-containing ore with a high carbonate modulus does not confirm a decrease in the flotation activity of calcite formed when studying monomineral calcite fractions, in contrast with fatty iso-alcohols, which make it possible to fabricate the higher quality concentrates in the selection cycle when compared with one oleate.

Understanding bubble growth process under decompression and its effects on the flotation phenomena

The aim of this study is to explore the effect of dissolved oxygen difference (DOD) on the formation of micro-nanobubbles and flotation systems. The nanobubbles on the calcite surface generated by the method of “Deep degassing water - saturated dissolved gas water exchange” were imaged by atomic force microscopy (AFM). Then, under decompression conditions, the micron-sized bubbles on the calcite surface were observed by a microscope digital camera. It was found that the growth rate of the micron-sized bubbles obeys the gas evolution rate equation under classical mechanics, which confirmed that the DOD under vacuum/decompression conditions is the decisive factor leading to the generation of micro-nanobubbles. At the same time, through a homemade vacuum Hallimond tube, the effects of the instantaneous gas evolution rate and the total amount of gas evolution on the single mineral flotation of calcite were investigated under a vacuum pressure of −50 KPa and a vacuum pressure of −70 KPa (The absolute pressure was 51 KPa and 31 KPa). The test results confirmed that if only the gas evolution rate is different, the recovery of calcite at a vacuum pressure of −70 KPa is 8.5% higher than that at a vacuum pressure of −50 KPa. However, if the gas evolution rate and total amount of gas evolution are simultaneously changed, the recovery of calcite at a vacuum pressure of −70 KPa is 12.31% higher than that at a vacuum pressure of −50 KPa. This result indicates that the formation rate and total amount of micro-nanobubbles have an important influence on flotation. At the same time, the proposal of DOD and the dynamic analysis of micro-nanobubble are good predictors for dissolved air flotation (including decompression flotation).

Depressants in nanoemulsion systems applied to quartz and hematite microflotation

Nanoemulsion systems were investigated in the microflotation of quartz and hematite. Four different depressants were used: Maizena®, soluble starch, amidex, and amylose. The nanoemulsions comprise in a single stable phase varying amounts of water, kerosene, Flotigam EDA® (collector), and n-butyl alcohol, allowing all flotation reagents to be added at the same time, reducing interfacial tension and favoring their application in the process. Microflotation tests were performed in a modified Hallimond Tube and the zeta potential values of the minerals were determined in the presence and absence of reagents. Quartz floatability was not affected by depressants, even when concentrations of 100ppm of depressant were used in the nanoemulsion. The determined isoelectric point of quartz (pH 2). High levels of hematite depression were obtained for all depressants (80%–90% depression). Quartz floatabilities of up to 95% were achieved by using nanoemulsions in the process.