Froth Layer Research Articles

Minimizing entrainment recovery of ultrafine silicate minerals in pentlandite flotation using carboxymethyl cellulose

The presence of silicate minerals is a common occurrence in various ore types, including nickel sulphide ores. These silicate minerals dilute the grade of flotation concentrates through recovery by entrainment which leads to poor flotation performance and subsequently loss of values. Flotation by entrainment is further enhanced as the particle size of the feed becomes finer. The present work investigates the entrainment characteristics of silicate minerals in the flotation of pentlandite. Within the context of the selective flotation of pentlandite from silicate gangue minerals, the influence of different particle sizes on entrainment flotation was also carried out. PAX was used as a collector for recovering pentlandite, whereas carboxymethyl cellulose (CMC) was employed as a dispersant for the silicate gangue mineral. Microflotation experiment was conducted on a pentlandite-quartz mixture of different particle sizes including − 106 + 75 µm, − 75 + 38 µm, − 38 + 20 µm, and − 20 µm. Electroacoustic zeta potential measurements, Fourier-Transform Infrared (FTIR) Spectroscopy, and Ultraviolet–Visible (UV–Vis) spectroscopy were used to characterise the interaction between pentlandite and quartz and in the presence of PAX and CMC. It was observed during the mixed minerals flotation tests that flotation by entrainment increased with a decrease in feed particle size irrespective of the dosage of CMC. Notwithstanding, the addition of CMC led to notable reduction in entrained silica flotation from 58 % to 38 % in the −20 µm size fraction attributed to improved particle drainage from the froth layer in the presence of CMC. Furthermore, UV–Vis spectroscopy and FTIR results gave further evidence that PAX adsorbed onto pentlandite and quartz minerals surfaces in the presence of CMC, which is consistent with the flotation response observed. Overall, this study confirms entrainment of gangue species is dominant within fine or ultra-fine mineral particles and proposes the use of CMC as a dispersant to limit gangue flotation by entrainment.

The role of microbubble dose in combined microflotation of fine particles

Flotation of small particles is one of the global challenges facing the mineral raw materials processing industry. Large amounts of non-ferrous and rare metals are lost in the flotation tailings in the form of mineral particles below 15 µm in size as a result of the low effectiveness of their capture by coarse bubbles generated in conventional flotation machines. The method of combined microflotation, developed in recent years, uses conventional coarse bubbles (CB) and microbubbles (MB) produced in the stand-alone generator of air-in-water microdispersion, which serves as the flotation carriers. Depending on the MB dose, the effect of their application may be positive or negative. The theoretical analysis of various mechanisms of particle transfer onto the surface of coarse bubbles and further into the froth layer allowed to obtain the formula for the optimal MB dose f=d<sub>d</sub>/2d<sub>p</sub>r<sub>p</sub>, where d<sub>d</sub> is MB size; d<sub>p</sub> and r<sub>p</sub> respectively are the size and the density of particles. Experiments performed on the copper ore flotation tailings at the Atalaya Mining (Spain) and Chaarat Kapan (Armenia) concentrators showed that, besides the optimal MB dose in the range of 1-3 ml/g, there is another optimal MB dose in the range of 10-20 ml/g, where the copper recovery increases by several percent compared to the reference test (f = 0). The deep minimum in copper recovery is observed in the area between the optimal MB doses, which is by several percent lower than the value in the reference test.

Enhanced coarse coal slime separation in a gravity–flotation coupled separator with up-flow feeding and dual-concentrate

ABSTRACT A gravity – flotation coupled separator with up-flow feeding and dual-concentrate was developed to improve the recovery and selectivity in coarse coal slime separation. The separator combines flotation, cyclone separation, and gravity sedimentation. The optimal separation performance was achieved under the following conditions: slurry concentration = 100 g/L, feed flow rate = 4.411 m3/h, circulating rate = 3.125 m3/h, fifigfeeding air flow rate = 2 m3/h, frother dosage = 150 g/t and collector dosage = 1500 g/t. Two concentrates were obtained with ash contents of 7.48% and 11.56%. The partition coefficients of the 0.75–1 and 0.5–0.75 mm fractions were 88.42% and 95.92%, respectively, indicating the satisfactory recovery of coarse particles. The ash content in the tailings was 66.08%, indicating good selectivity. The diverging flow under the froth layer produced a coarse concentrate, which improved the recovery of the concentrate and reduced the flotation concentrate ash content. The total recovery of the concentrate blended with the + 0.25 mm fraction of diverging flow was 84.00%. Both up-flow and cyclone separation are beneficial for coarse particle recovery. The static separation cone is instrumental in improving the separation effect. Therefore, this wide-sized coal-slime separator facilitates the effective separation of both coarse and fine particles.

Effects of carrier particles on flotation removal of unburned carbon particles from fly ash

Fly ash, a major by-product of coal-fired power plants, contains unburned carbon which poses challenges to its effective utilization. The flotation separation efficiency of unburned carbon from fly ash is limited due to the ultrafine size and poor hydrophobicity of the unburned carbon. This study introduces carrier flotation as an efficient method for removing unburned carbon from fly ash. Experimental results indicated that the use of carrier particles (low ash content coal particles) significantly enhanced the flotation removal efficiency of unburned carbon from fly ash compared to conventional methods. The enhancement mechanism was evaluated by examining the differences in flotation froth properties, particle aggregation behaviors, and extended Derjaguin-Landau-Verwey-Overbeek (EDLVO) interaction energy in the presence and absence of hydrophobic carrier particles. Hydrophobic carrier particles were found to increase the stability of the flotation froth layer, facilitate the water recovery, and aid in the removal of fine unburned carbon particles. Focused beam reflectance measurement (FBRM) confirmed that the presence of hydrophobic carriers promoted the aggregation of fine unburned carbon particles, thereby increasing bubble-particle collision probability. Furthermore, EDVLO theory calculations revealed that the attractive interaction energy between carrier particles and unburned carbon particles was stronger than that between carrier particles and ash particles. Therefore, carrier flotation shows promise as a highly efficient method for removing unburned carbon from fly ash.

The effects of indigenous microorganisms and water treatment with ion exchange resin on Cu-Ni flotation performance

Mineral processing utilizes large amounts of water and aims to reduce water consumption by recirculation and closing the water loops. This results in accumulation of chemical and biological contaminants in process water that may have adverse outcomes on the process performance. To optimize water quality suitable for each process step and plant, knowledge of both chemical and biological effects are needed as well as techniques to best remove the contaminants. This study focused on the consequences of microorganisms, enriched from the actual process earlier, on the flotation performance in the multi-metal Kevitsa mine in Northern Finland and the applicability of ion exchange for the removal of dissolved sulfur species and microorganisms from water. The increase of microbial load from the original 106 to added 107 16S rRNA copies mL−1 affected positively the flotation selectivity, especially in the case of nickel. Two tested water types, process water (PW) and final tailings water (FT), behaved slightly differently. In the Cu flotation phase added microorganisms did not affect the Cu recovery of FT but decreased significantly the recovery of Cu in PW. With equal Cu grade, the recovery was as high as approximately 25 percentage points lower. However, added microorganisms in both water types decreased notably the recovery of Ni in Cu concentrate (18 to 37 %-points). At the same time the amount of Ni recovered in the Ni concentrate increased by 18 to 33 %-points with added microorganisms. Visually the froth layer was higher and more stable in the Ni flotation in experiments with added microorganisms compared to experiments without added microorganisms. The concentrations of dissolved sulfate and thiosulfate ions were low in the studied waters compared to operations treating massive sulfide ores and did not significantly affect the flotation performance. For this reason, the IX water treatment was not required for these ions. However, the IX treatment proved to be effective in removing both sulfur species and microorganisms. The use of dissolved air flotation (DAF) was a successful pretreatment for ion exchange in removal of microorganisms. However, microorganisms are not usually taken into consideration when process performance or water cleaning techniques are designed and optimization could result generally in even better outcome.

Effects of Sec-Octanol and Terpineol on Froth Properties and Flotation Selectivity Index for Microcrystalline Graphite

Microcrystalline graphite is a valuable non-metallic mineral that can be separated by flotation, a physico-chemical processing method that uses air bubbles to capture mineral particles. The size and stability of the bubbles, which depend on the type and amount of frother added, affect the flotation performance and the recovery of water from the froth layer. However, the effects of different types of frother on the froth properties and water recovery of microcrystalline graphite flotation are not well understood. In this study, two common frothers, sec-octanol and terpineol, were compared in terms of their effects on the bubble size, froth layer height, water recovery, and flotation selectivity index (SI) of microcrystalline graphite flotation. It was found that sec-octanol produced smaller bubbles than terpineol, but also a slightly lower froth layer height. The water recovery was higher with sec-octanol than with terpineol. The SI values were similar for both frothers, indicating comparable flotation performance. This study revealed the differences between sec-octanol and terpineol in terms of their effects on the froth properties and water recovery of microcrystalline graphite flotation. These findings can help optimize the choice and dosage of frother for this important mineral processing method.

Removal of Silicon from Magnesite by Flotation: Influence of Particle Size and Mechanical Mechanism.

The feasibility of producing high-density sintered magnesia with a one-step sintering method was investigated by utilizing finely ground magnesite as raw materials for direct flotation. The mechanism of flotation desilication of microfine grain magnesite was investigated by combining microstructure and chemical properties. The results showed that dodecylamine (DDA) has a sorting effect on magnesite reverse flotation desilication. Under the premise of 150 mg/L sodium polyacrylate (PAANa) as an inhibitor and 300 mg/L DDA as a collector, the content and recovery rate of MgO can reach 83.91% and 78.78%, respectively. When sodium oleate (NaOL) was used as a collector, the recovery rate of MgO was only 49.22%; therefore, it is unsuitable for magnesite purification. The flotation effect was affected because MgO particles and SiO2 particles agglomerated in the flotation process. The flotation agent cannot work for a single element but works for the mineral agglomerate. While collecting Si elements, the agglomerated MgO was also brought into the froth layer, making flotation impossible.

Extremum seeking control to optimize mineral recovery of a flotation circuit using peak air recovery

A flotation circuit is controlled in simulation using an extremum seeking control (ESC) approach to keep the cells operating at the optimal operating point, as represented by peak air recovery. It is assumed that optimal performance is achieved at this operating point where the froth layer is stable, and the mineral recovery of the flotation cell is maximized. Two gradient-based ESCs, a classical perturbation-based ESC and a time-varying ESC, as well as a non-gradient-based direct search Nelder–Mead simplex ESC, are compared on the flotation circuit to steer the plant through an unknown static map towards the peak in air recovery. The three ESCs can respectively optimize the flotation circuit and find the peak air recovery operating point. The simplex ESC can converge quickly to the optimum but does not adapt to changing conditions. The gradient-based ESCs can track the time-varying peak air recovery operating point and adapt to an external disturbance. Although the three ESC methods are not dependent on a process model to optimize the plant, their convergence times are relatively slow. The ESCs are ideally suited for model-independent long-term automated optimization of a flotation circuit with a slow time-varying optimal operating point.

Double‐sensor conductivity probe applied in a flotation system

AbstractThis study proposed a new approach for measuring bubble size distribution, bubble mean diameter, Sauter mean bubble diameter, and gas holdup using a double‐sensor conductivity probe in an air/water two‐phase system bubble column. The results for the two‐phase system were compared and calibrated using analyses from bubble images taken by a digital camera from the side of the column wall. Good agreement was observed between the two techniques. The same double‐sensor conductivity was used in an air/water/solids three‐phase system. The conductivity probe captured the change in bubble dynamic behaviour inside the pulp phase; however, the presence of the solids made it more challenging to measure. As a result, the VisioFroth commercial package, using images taken from the top of the froth layer, could be used in conjunction with the double‐sensor conductivity probe to show the dynamic evolution of mineralized bubbles from the pulp zone to the froth zone in a flotation process.

Online detection of concentrate grade in the antimony flotation process based on in situ Raman spectroscopy combined with a CNN-GRU hybrid model

Froth flotation is the most critical process for separating stibnite from raw ore. Concentrate grade is a vital production indicator in the antimony flotation process. It is a direct reflection of the product quality of the flotation process and an essential basis for the dynamic adjustment of its operating parameters. Existing methods of measuring concentrate grades suffer from expensive measurement equipment, difficult maintenance of complex sampling systems, and extended testing times. This paper presents a nondestructive and fast methodology to quantify the concentrate grade in the antimony flotation process based on in situ Raman spectroscopy. A particular Raman spectroscopic measuring system is designed for on-line measurement of the Raman spectra of the mixed minerals from the froth layer during the antimony flotation process. To obtain representative Raman spectra that better characterize the concentrate grades, a traditional Raman spectroscopic system has been redesigned to account for the different interferences during actual flotation field acquisition. A one-dimensional convolutional neural network (1D-CNN) is combined with a gated recurrent unit (GRU) and applied to construct a model for online prediction of concentrate grades based on continuously collected Raman spectra of mixed minerals in the froth layer. With an average prediction error of 4.37% and a maximum prediction deviation of 10.56%, the quantitative analysis of concentrate grade by the model demonstrates that our method is distinguished by high accuracy, low deviation, and in situ analysis, and it essentially satisfies the requirements for online quantitative determination of concentrate grade in the antimony flotation site.

A Model of Froth Flotation with Drainage: Simulations and Comparison with Experiments

The operation of a froth flotation column can be described by a nonlinear convection–diffusion partial differential equation that incorporates the solids–flux and drift–flux theories as well as a model of foam drainage. The resulting model predicts the bubble and (gangue) particle volume fractions as functions of height and time. The steady-state (time-independent) version of the model defines so-called operating charts that map conditions on the gas and pulp feed rates that allow for operation with a stationary froth layer. Operating charts for a suitably adapted version of the model are compared with experimental results obtained with a laboratory flotation column. Experiments were conducted with a two-phase liquid–bubble flow. The results indicate good agreement between the predicted and measured conditions for steady states. Numerical simulations for transient operation, in part for the addition of solid particles, are presented.

Effect of freezing-air thawing pretreatment of cutting fluid wastewater on the organics' distribution, transfer and transformation

The cutting fluid wastewater was treated by freezing-air thawing method. After thawing, stable stratification occurred in the thawing wastewater, and the froth floated on the liquid surface, and the liquid from top to bottom was divided into the first layer, the second layer, the third layer and the fourth layer. The molecular weight (MW) distribution and organics characteristics of the froth layer and each layer wastewater were analyzed by ultrafiltration membrane filtration combined with mass balance, three-dimensional fluorescence excitation-emission matrix spectroscopy, ultraviolet absorption spectroscopy, flourier transform infrared spectroscopy and droplet size analysis. The results showed that the cutting fluid wastewater contained 66.74 % organics with MW > 100 kDa and 17.04 % organics with MW < 1 kDa, and the organics might contain aromatic and heterocyclic compounds. After three times of freezing-air thawing: 27.53 % of organic matter was volatilized into the air; the froth layer was mainly macromolecular organic matter with MW > 100 kDa, accounting for 94.59 %; from the froth layer to the fourth layer wastewater, the content of macromolecules with MW > 100 kDa gradually decreased, while the content of small molecules with MW < 1 kDa gradually increased. The results of molecular weight distribution analysis, spectroscopy analysis and droplet size analysis indicated that during the freezing-air thawing process, there was not only the demulsification maybe but also the destruction of molecular structure. The molecular weight distribution of the mixture of the froth layer and the fourth layer wastewater were close to that of the raw cutting fluid wastewater, so the mixture of the froth layer and the fourth layer wastewater could be reused in metal process. The wastewater in the first, second and third layers had better biodegradability, which could be treated by biological method.

Improved Separation between Recycled Anode and Cathode Materials from Li-Ion Batteries Using Coarse Flake Particle Flotation

Separation between two recycled electrode active materials from spent Li-ion batteries by a conventional froth flotation method has been challenging due to similarity in their surface hydrophobicity. In this study, a new coarse flake particle flotation technology has been developed to separate the electrode active materials from Li-ion batteries. The new process separates the recycled electrode flake particles effectively at a size range of 212–850 μm by taking advantage of a significant difference in densities between the anode flake materials and cathode flake materials. At a feed size of 212 μm or less, a fraction of recycled cathode particles is floated in the froth layers resulting in a loss of cathode materials in the sink product. At a feed size of 850 μm or above, a small fraction of anode flakes becomes non-floatable, resulting in a decrease in the grade of cathode materials in the sink product. The mechanism has been investigated by induction time measurements, bubble–flake detachment, contact angle measurements, and force analysis. The anode flakes are more hydrophobic than cathode flakes, which is consistent with the result obtained from induction time measurements. A force analysis reveals that the critical size for electrode flake particles being attached to air bubbles varies with advancing contact angle and density. Maintaining a desirable feed size is essential to achieve an optimum separation performance. In this regard, a flotation column is superior to mechanical flotation cells in minimizing size reduction during the flotation process. Lab-scale column flotation trials showed that a good separation between anode and cathode flake particles has been achieved by column flotation with 98–99% purity of cathode flake materials in the sink product at a recovery rate of 96–99%. The present study demonstrates a new process in separating two electrode flake materials from spent Li-ion batteries.

Разработка и настройка алгоритма программной идентификации отклонений в пенном слое калийной флотомашины

The article deals with the problems that arise in the practical application of the method of glare recognition of the parameters of the froth layer of a potash ore flotation machine. These include choosing the best statistical characteristic, filtering and averaging settings, checking the possibility of taking into account anti-glare, and the need for adaptive signal renormalization. Objective of the study is to develop an algorithm for identifying a flotation cell as an object of automatic control, which is possible only after solving these problems. Materials and methods of research. The study was carried out on the materials of an experimental survey of a potash flotation machine. During the shooting, a standard step signal was applied to the machine cell, which was expressed in a change in the composition of the amino-oil mixture, which caused a transient process. For different statistical characteristics (the number of bubbles, the number of red components in the frame, the average and median distances between the centers of the bubbles), various methods of filtering and averaging the data were tested. At the same time, the problem of identifying the gain and the time constant of the object was solved. The best characteristic and methods of its processing were chosen on the basis of the root-mean-square deviation of the calculated transient process from field data obtained by glare recognition of the foam layer surface. Results. Processing several frames in a row, taken at the same position of the foam, slightly improves the result, but significantly loads computing power. Blind filtering by ten points has practically no effect on the data processing time. To improve the identification, data renormalization was used, which consists in the adaptive selection of the zero and single signals in the conditions of noisy data. The localization method was used to determine the optimal delay from the point of view of the quadratic deviation before the start of the transient process. Conclusion. As a result, the best filtering and data averaging settings were obtained, providing the smallest identification error. The time constant of the cell turned out to be close to the results of previous authors, obtained, among other things, by visual observation of the flotation machine. Accounting for antiglare does not significantly affect the parameters of the object. An important conclusion is that one statistical characteristic describes well the beginning of the transient process, and the other describes its end. This must be taken into account when building a deviation signaling system.

A methodology to implement a closed-loop feedback-feedforward level control in a laboratory-scale flotation bank using peristaltic pumps

This paper describes the implementation of a level control strategy in a laboratory-scale flotation system. The laboratory-scale system consists of a bank of three flotation tanks connected in series, which mimics a flotation system found in mineral processing plants. Besides the classical feedback control strategy, we have also included a feedforward strategy to better account for process disturbances. Results revealed that the level control performance significantly improves when a feedforward strategy is considered.This methodology uses peristaltic pumps for level control, which has not been extensively documented even though: (1) peristaltic pumps are commonly used in laboratory-scale systems, and (2) the control implementation is not as straightforward as those control strategies that use valves. Therefore, we believe that this paper, which describes a proven methodology that has been validated in an experimental system, can be a useful reference for many researchers in the field.•Preparation of reagents to ensure that the froth stability of the froth layer is representative of an industrial flotation froth.•Calibration of instruments – convert the electrical signal from PLCs to engineering units.•Tuning PI parameters using SIMC rules by performing step-changes in each flotation cell.

A degenerating convection–diffusion system modelling froth flotation with drainage

Abstract Froth flotation is a common unit operation used in mineral processing. It serves to separate valuable mineral particles from worthless gangue particles in finely ground ores. The valuable mineral particles are hydrophobic and attach to bubbles of air injected into the pulp. This creates bubble-particle aggregates that rise to the top of the flotation column where they accumulate to a froth or foam layer that is removed through a launder for further processing. At the same time, the hydrophilic gangue particles settle and are removed continuously. The drainage of liquid due to capillarity is essential for the formation of a stable froth layer. This effect is included into a previously formulated hyperbolic system of partial differential equations that models the volume fractions of floating aggregates and settling hydrophilic solids [R. Bürger, S. Diehl and M.C. Martí, IMA. J. Appl. Math. 84 (2019) 930–973]. The construction of desired steady-state solutions with a froth layer is detailed and feasibility conditions on the feed volume fractions and the volumetric flows of feed, underflow and wash water are visualized in so-called operating charts. A monotone numerical scheme is derived and employed to simulate the dynamic behaviour of a flotation column. It is also proven that, under a suitable Courant-Friedrichs-Lewy condition, the approximate volume fractions are bounded between zero and one when the initial data are.

The effect of collectors on froth stability of frother: Atomic-scale study by experiments and molecular dynamics simulations

The effect of sodium diethyldithiocarbamate (DDTC)/butyl xanthate (BX) on froth stability formed by methyl isobutyl carbinol (MIBC) was investigated using experiments and molecular simulations, and the mechanism of the effect of differently structured collectors on the interfacial water at the gas–liquid interface was discovered. The froth stability indicated that DDTC and BX could considerably reduce the solution surface tension, increase the froth half-life, and maximum froth layer volume compared with MIBC solutions. Particularly, in the BX-containing system, the froth half-life reached an astonishing 160 s, and the maximum froth layer volume reached 270 ml. To explain this observation, this study used molecular simulations to provide new insights into the interactions between DDTC/BX and MIBC and water at the molecular level. The results demonstrate that the density of water molecules at the interface of the DDTC/BX solution is higher than that of the MIBC solution, the orientation of water molecules at the interface is more ordered, and the hydrogen bonds are more tightly connected. The results are consistent with the experimental data, demonstrating that DDTC/BX improves the significance of MIBC on water molecule rearrangement at the gas–liquid interface. This study can offer a reference for studying the effect of collector structure on frother performance and can offer important guidance for the design of mineral flotation reagents.

Extremum Seeking Control of a Flotation Circuit using Peak Air Recovery

A flotation circuit is simulated with an extremum seeking controller to keep the cells operating at the optimal operating point represented by peak air recovery. It is assumed that at this operating point, the froth layer is stabilised and the mineral recovery of the flotation cell is maximised resulting in optimal performance. The extremum seeking controller uses periodic perturbations in the aeration rate to steer the system through an unknown static map towards the peak in air recovery. The controller is able to find the peak air recovery operating point and track the point as it changes in the presence of external disturbances. The extremum seeking controller is ideally suited for model-independent long-term automated optimisation of a flotation circuit with a time-varying optimal operating point.

Insight into the low-rank coal flotation using amino acid surfactant as a promoter

Low-rank coal flotation faces challenges due to its poor surface hydrophobicity. Massive oily collector, e.g. kerosene and diesel, are needed to improve its flotation performance, causing huge cost input. This study experimentally demonstrated that Sodium Cocoyl Glycinate (SCG), an amino acid surfactant, could help with obtaining higher efficiency when adopted in low-rank coal flotation. Results showed that compared with the condition using kerosene (5000 g/t) alone, a tiny amount of SCG (50 g/t) increased the concentrate yield by about 12%, while its ash content roughly remained the same. Effects of SCG on low-rank coal flotation was established from coal surface hydrophobicity, solution surface tension and the forth layer. The amphipathic groups of Sodium Cocoyl Glycinate would bond both with the hydrophilic and hydrophobic sites on the coal surface through hydrogen bonding, leaving the hydrophobic end exposed, which shorten the bubble-particle attachment time to about 100 ms. The decrease of solution’s surface tension was conducive to the emulsification of kerosene, making droplets diameter distribution into a smaller range of 0.26 to 10 μm. Meanwhile, lower surface tension offset the negative impact of oily collector, providing a more stable froth layer. Considering its hypotoxicity, biodegradability, environmental friendliness, Sodium Cocoyl Glycinate could be a green flotation promoter assisting with the conventional oily collectors.

Finishing of gold-bearing concentrated products

The research data on the finishing centrifugal flotation of the pre-concentrated gold-antimony ore product are reported on a series of laboratory tests at a centrifugal flotation machine with peripherical discharge of the concentrate (CFM) and a mechanical flotation machine (FM). The selectivity of mineral particle detachment from the mineralized flotation froth moving along an inclined plane after flotation process running at different modes with/without a collector. It is demonstrated that the use of a collector makes it possible to control intensity and selectivity of material detachment from the froth layer. It is found that flotation finishing in the centrifugal flotation machine actually enables to improve the final concentrate characteristics.