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1.
A model is developed by taking into account the simultaneous mechanisms of true flotation and entrainment in a conventional flotation cell. The total volume of the cell is divided into three compartments: pulp collection zone, pulp quiescent zone and froth region, with the mechanisms being modeled as occurring at the same time but originating at different places: true flotation from the collection zone and entrainment from the quiescent one. A particle is referred to as suspended in water or attached to an air bubble, depending upon its original state before crossing the pulp–froth interface (whether or not it remains in that state all the way to the concentrate launder). The model is obtained by solving a set of equations describing the mass conservation of solids and water between adjacent compartments. The principal mass transfer factors are identified as: the flotation rate constant, the mean residence time in the collection zone, the froth recovery of attached particles, the degree of entrainment through the froth and the water recovery from the feed to the concentrate. The development presented here allows the intricate nature of the mass transfer in a flotation cell to be reduced to one single equation, overcoming the need of numerical methods for simulation purposes. Moreover, it is shown that reliable prediction of grade and recovery can be obtained without detailed information on the pulp hydrodynamics or on any froth sub-process either than drainage, bubble bursting and bubble coalescence.  相似文献   

2.
Tracer experiments using quartz in sized ranges to simulate gangue minerals provide information on how impeller speed, air rate, and particle size determine the concentration of gangue in the uppermost pulp layers. Tests with and without a froth will contribute towards an understanding of the selective action of the froth column.Results indicate that the laboratory machine-operating conditions required for flotation coincide with a hydrodynamic region which is responsible for fine-gangue transfer from the pulp into the froth column by elutriation and entrainment process acting in the pulp, thus compromising the selective action of the flotation process itself.Topics are suggested requiring further investigation and mention is made of machine design features to which attention should be paid in attempting to reduce gangue transfer from pulp to froth.  相似文献   

3.
The flotation rate of galena was investigated as a function of air flow rate (AFR) and froth thickness (from 0 to 6 cm) in a batch flotation cell designed to produce a quiescent froth-liquid interface. This cell design limits mechanical breakage of the froth and prevents the hydraulic entrainment of fine particles into the froth phase. The overall transfer rate was characterized by a first-order rate constant, the overall rate constant (ORC). The ORC was found to increase with increasing AFR and with decreasing froth thickness. The transfer rate of material from the slurry to the froth was also determined as a function of AFR, and characterizes by its first-order rate constant, the flotation rate constant (FRC).The froth transport constant (FTC), the first-order constant which characterizes the transport of galena from the froth over the cell lip, was then determined from the ORC and the FRC. The FTC was found to increase with increasing AFR and decreasing froth thickness. For a froth thickness of 5 cm and low-to-intermediate AFR, the FTC was found to be significantly lower than the FRC.The FTC of galena particles of 0–12, 12–32 and 22–40 μm was also determined. At a froth thickness of 5 cm, the FTC decreased with increasing particle size over the full experimental range of AFRs.  相似文献   

4.
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5.
The need to obtain accurate, operator-independent data from small-scale laboratory flotation tests has become particularly apparent in the treatment of fine coal. The work described suggests a method for reducing operator dependency by removing the flotation froth uniformly. This is achieved using a perspex insert to change the geometry of the cell, by maintaining a constant pulp level height and by removing froth from the full width of the cell and at a fixed depth.A comparison is made between the modified cell and a conventional Denver cell by obtaining equilibrium and kinetic data for each cell from two independent operators.The comparison shows a reduction in the variability of the results obtained from the modified cell.  相似文献   

6.
Effects of aeration rate, slurry flow rate, stirring rate, pulp density, and particle size on the residence time distribution of a solid in a continuously operated flotation cell under non-flotation conditions (no frother, no concentrate removal) have been examined. The mixing behaviour of the solid in the cell has been quantitatively analysed using a multiple parameter approach. The results indicate that only a part of the cell volume behaves as a perfect mixer, the remaining being dead. The exit residence time distribution E(t) and the mean residence time ( ) of solid are described by: and where Q is the volumetric slurry flow rate. For the variables ranges examined, it is observed that the aeration does not have any significant effect on the mixing behaviour, Veff increases with increasing slurry flow rate and stirring rate but decreases with increasing pulp density. The mean residence time, on the other hand, increases with increasing stirring rate, decreases with increasing slurry flow rate and pulp density, and exhibits a maximum with respect to particle size. Following empirical equation correlating the effective volume of the cell with the operating variables for a unisize feed is obtained: where B is the weight fraction of solid in the pulp.  相似文献   

7.
Both froth flotation and centrifugal concentration were used to pre-concentrate the oil sands froth treatment tailings prior to the recovery of heavy minerals (titanium and zirconium minerals). Over 90% of the heavy minerals were recovered into a bulk flotation concentrate that was about 50% of the feed mass at 85 °C without any reagents. The same recoveries were obtained at 50 °C with the addition of NaOH and/or sodium oleate. However, the flotation concentrate also recovered over 90% of the residual bitumen and much of the clays/slimes. Subsequent treatment of the flotation concentrate such as dewatering and bitumen removal would be difficult due to these residual bitumen and clays. On the other hand, a SB40 centrifugal concentrator recovered over 85% of the heavy minerals but less than 30% of the residual bitumen. With improved liberation the recovery of the residual bitumen into the concentrate could be further reduced. The particle sizes of the SB40 concentrates were also larger than the flotation concentrates, making subsequent processing much easier.  相似文献   

8.
The limitations of pulp chemistry measurements in the flotation of a platinum group mineral (PGM) bearing Merensky ore were demonstrated in Part 1 of this article. In this paper the importance of the contribution of the froth structure due to changing froth stability is analysed using the batch flotation data. The effects of mild steel (MS) and stainless steel (SS) milling media and the addition of copper sulphate on the flotation performance of the sulphide minerals in Merensky ore have been evaluated in relation to the changes in stability of the froth phase. The effects of pulp chemistry and froth stability on the flotation of sulphide minerals were distinguished by using two different rate constants (kt and kw). The rate constant (kw) calculated as a function of cumulative water recovery was used to describe characteristics of froth phase and kt was calculated as a function of flotation time. The results revealed that the type of grinding media and copper sulphate addition had an interactive effect on the froth stability. While mild steel (MS) milling increased the froth stability due to the presence of hydrophilic iron hydroxides and colloidal metallic iron, the addition of copper sulphate reduced the stability, especially with stainless steel (SS) milling. Copper sulphate addition had a dual role in the flotation of Merensky ore in that it caused destabilisation of the froth zone as well as activation of selected sulphide minerals. The dominant effect was found to depend on the type of milling media and floatability of the mineral in question and this work has demonstrated the importance of using a combination of measurements to evaluate flotation performance holistically.  相似文献   

9.
Data are presented which illustrate a range of flotation behaviour observed for roughing and cleaning operations in industrial plants. Differences are observed in the size by size recoveries in cleaner flotation from those measured in the roughers.The implications of these differences to flotation modelling are discussed, and the importance of conducting confirmatory laboratory batch flotation tests is emphasized.Batch flotation tests have indicated that for certain minerals the flotation characteristics in the cleaner tests are substantially different from those in rougher tests conducted under the same conditions of pulp level, impeller speed, aeration rate and froth removal. The differences are most pronounced for the coarse particles.Computer simulations of a rougher-cleaner circuit have been done to illustrate the effects of these differences on predicted circuit performance. The differences are significant and arise mainly from differences in the behaviour of coarse particles.  相似文献   

10.
The properties of thin liquid films (TLF) are of paramount significance for colloidal disperse systems, and a number of industrial processes, including froth flotation. In flotation, the bubble–particle attachment is controlled by the thinning and rupture of the intervening liquid film between an air bubble and a mineral particle. The froth evolution and its transient stability are also a function of the drainage and rupture of liquid films between air bubbles. Surface-active substances (surfactants) are used as flotation reagents to control the behavior of the liquid films. This paper presents a review of our research in the area of surfactant adsorption, surface forces and liquid films. It mainly focuses on the validation, application and extension of the Stefan–Reynolds theory on the liquid drainage. The extension of the Stefan–Reynolds theory comprises surface forces (disjoining pressure), surface tension variation, caused by the adsorption and diffusion of surfactants. Both the experimental and theoretical results are mostly related to the free (foam) films formed between two bubbles but can be principally extended to emulsion films between two oil drops and wetting films between an air bubble and a solid surface.  相似文献   

11.
The effect of particle shape on the flotation process has been investigated in laboratory experiments with monosized spherical ballotini and ground ballotini. The particles were treated by partial methylation with trimethylchlorosilane to achieve varying degrees of hydrophobicity. In flotation, the process of film thinning and liquid drainage is critical in the formation of stable bubble–particle attachments and this is affected by the particle shape and surface hydrophobicity. Flotation tests with different particle sizes were conducted in a modified batch Denver cell. Predictions from a computational fluid dynamic model of the flotation cell that incorporates fundamental aspects of bubble–particle attachment were compared with data from flotation tests. Contact angles of the particles were measured using a capillary rise technique to indicate surface hydrophobicity. Ground ballotini generally has higher flotation rates than spherical ballotini; the results are consistent with effects from faster film thinning and rupture at rough surfaces and are well correlated by the sphericity index.  相似文献   

12.
It is well known that the chemical environment determines the success of the flotation process, however its characterisation and control is difficult to achieve. This paper, as two parts, Part I and Part II, evaluates the use of various measurements and their interpretation to gain an understanding of the influence of varying parameters such as the type of milling media and copper sulphate addition on the flotation performance of sulphide minerals from a platinum group mineral (PGM) bearing Merensky ore. It shows the complexity of interpretation and the importance of analysing flotation performance holistically. Part I focuses on the pulp chemistry and mineral potential measurements have been used to show the differences in the response of the various mineral electrodes to different conditions. The final flotation recoveries of the sulphide minerals in the ore followed the same trend as the decrease in mineral potential due to collector addition viz. chalcopyrite > pentlandite > pyrrhotite. Type of milling media and copper sulphate addition slightly affected the mineral electrode potential and flotation recovery of chalcopyrite. Addition of copper sulphate increased the recovery of pentlandite and particularly pyrrhotite due to activation by copper (II) ions. The copper activation mechanism was likely to be in the form of initial adsorption of copper hydroxide followed by reduction to Cu+ at the surface. However, the changes in flotation performance of the different minerals in the ore could not be completely described by the electrochemical changes, demonstrating the limitations of these measurements. Part II addresses the effect of froth stability as demonstrated by the variations in the mass and water recovery data resulting from the different milling conditions and addition of copper sulphate which emphasised the importance of considering the froth phase in the evaluation of flotation data.  相似文献   

13.
The importance of the cleaning action of the froth has been recognised. In order to observe the effect of various mechanisms on the gradients of mineral concentration in the froth, experiments were performed in a flotation cell using a deep froth phase where transverse motion of the froth was reduced to a minimum. The variables chosen for study include gas rate, baffling of the froth and product removal rate. The mineral studied comprised a mixed Cu, Zn and Fe sulphide with a siliceous gangue. A model based on counter-current plug-flow assumptions is advanced to describe some of the effects observed. A number of these effects are simulated using this model, leading to a better understanding of some of the processes occurring in the froth.  相似文献   

14.
Bubble size distributions and flotation rates were determined as a function of air flow rate and frother concentration using a specially designed batch flotation cell. This cell permitted the unambiguous determination of the flotation rate from the slurry to the froth.Flotation rate constants were determined for different size classes of silica and galena. The flotation rate constants increased to a maximum and then decreased as air flow rate was increased. This maximum was predicted by a model which considered the effect of bubble size on both the total bubble surface area and the bubble-particle collision efficiency. This work shows that collision efficiency effects, shown to exist in single-bubble/single-particle systems, are also present in flotation systems where many bubbles and particles interact.A second model for hindered flotation is proposed which assumes that the particle-capturing bubble surface differs from the particle-retaining surface. This model predicts a sharp transition from hindered to free flotation. Experimental results are presented which agree well with those derived from the model.  相似文献   

15.
The detailed flotation behaviour observed in industrial zinc cleaning circuits at Broken Hill differs markedly from that commonly reported for rougher and scavenger flotation. Flotation is strongly influenced by solids to liquid ratio (pulp density) and the behaviour can be described by an exponential relationship between the flotation rate coefficient and the pulp density in each cell. The dependence on pulp density is largely independent of mineral type but does depend upon particle size. The largest variation is observed for coarse particles.The observations are of considerable significance to control of circuit performance. The results of simulations incorporating the dependence of rate coefficient upon pulp density differ substantially from those obtained from conventional models which assume constant rate coefficients.  相似文献   

16.
Models in which the cell contents are partitioned into distinct pulp and froth phases are reviewed critically. The nature of the mixing within the phases is discussed. Multiphase models describing froth column concentration gradients and pulp residence time effects are mentioned. It is shown that at steady state multiphase models can be reduced to the two-phase case. Deficiencies in the models and topics requiring further development are outlined.  相似文献   

17.
The paper discusses the obstacles in the way of making mathematical models of flotation circuits for use in process design; and describes also a route towards simple, but practical, models of full-scale flotation plant performance, which overcome the major problems. The principal difficulties lie in simulating the froth processes at full-scale. Timed batch tests may be used to identify the pulp-froth transfer processes, and steady-state (“equilibrium”) cell tests may be used to identify static froth concentration profiles. Froth mobility in a real cell is different from that in an “equilibrium” cell, and this paper shows how these dynamic patterns have been investigated, and may be used to simulate full-scale circuits. It is shown that it is not possible, at the present time, to completely eliminate judgement and experience from the establishment of parameter values; but the position should improve as experience accumulates.  相似文献   

18.
Effects of particle size and chain length on flotation of quaternary ammonium salts (QAS) onto kaolinite have been investigated by mico-flotation tests. The two kinds of quaternary ammonium salts [RN(CH3)3] with different chain lengths, dodecyltrimethylammonium chloride (DTAC) and cetyltrimethylammonium chloride (CTAC) were used as collectors for kaolinite in different particle size fractions (0.075–0.01 mm, 0.045–0.075 mm, 0–0.045 mm). The anomalous flotation behavior of kaolinite have been further explained based on crystal structure considerations by adsorption tests and molecular dynamics (MD) simulation. The results show that the flotation recovery of kaolinite in all different particle size fractions decreases with an increase in pH when DTAC and CTAC are used as collectors. As the concentration of collectors increases, the flotation recovery increases. The longer the carbon chain of QAS is, the higher the recoveries of coarse kaolinite (0.075–0.01 mm and 0.045–0.075 mm) are. But the flotation recovery of the finest kaolinite (0–0.045 mm) decreases with chain lengths of QAS collectors increasing, which is consistent with the flotation results of unsifted kaolinite (0–0.075 mm). It is explained by the froth stability related to the residual concentration of QAS collector. In lower residual concentration, the froth stability becomes worse. Within the range of flotation collector concentration, it's easy of CTAC to be completely adsorbed by kaolinite in the particle size fraction (0–0.045 mm), which led to lower flotation recovery. Moreover, it is interesting that the particle size of kaolinite is coarser, the flotation recovery is higher. The anomalous flotation behavior of kaolinite is rationalized based on crystal structure considerations. The results of MD simulations show that the (001) kaolinite surface has the strongest interaction with DTAC, compared with the (001), (010) and (110) surfaces. On the other hand, when particle size of kaolinite is altered, the number of basal planes and edge planes is changed. It is observed that the finer kaolinite particles size become, the greater relative surface area of edges is, and the more the number of edges is. It means that fine kaolinite particles have more edges to adsorb less cationic colletors than that of coarse kaolinite particles, which is responsible for the poorer floatability of fine kaolinite.  相似文献   

19.
Accurately estimating entrainment is crucial when predicting flotation performance as it is essential for determining the concentrate grade achieved. It has been found previously that the amount of gangue entrained is proportional to the water recovery; this proportionality is referred to as the entrainment factor. Experimentally it has been found that entrainment is a strong function of particle size, as well as being dependent on other cell operating parameters such as froth depth and air rate.A simplified theoretical model for entrainment is developed which includes the effects of liquid motion and content, particle settling and particle dispersion. First, a detailed one-dimensional differential model for the entrainment factor is developed and solved numerically. Thereafter, a simplified analytical expression for the entrainment factor is produced which is a good approximation to the more detailed one-dimensional model. Both these models are shown to predict closely experimental trends for entrainment as a function of particle size and froth depth.  相似文献   

20.
Potato starch and dextrins resulting from thermolysis of potato starch in the absence of reagents and presence of -amino acids are promising depressants for separation of lead and copper minerals present in the Polish industrial copper concentrates. The polysaccharides were used for differential xanthate flotation of the final industrial concentrates produced by flotation with sulfhydryl collectors in the absence of depressants. The polysaccharides depressed galena and provided froth concentrate rich in chalcocite and other copper minerals as well as cell product containing lead minerals. The best results of separation were obtained in the presence of plain dextrin prepared by a thermal degradation of potato starch. The industrial concentrate containing 18.5% Cu and 5.5% Pb was divided into a froth product containing 38.1% Cu with 77% recovery of copper and a cell product assaying 7.3% Pb with 83% recovery of lead. It was accomplished using 2500 g/t of dextrin, 50g/t of potassium ethyl xanthate, and 50 g/t of frother (α-terpineol). The pH of flotation was 8.0–8.2.  相似文献   

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