Determination of the contributions of true flotation and entrainment in batch flotation tests

Laboratory batch flotation tests were carried out on a deslimed (+6 μm) sulfiderich cassiterite ore, an ultrafine fraction (?6 μm) of a cassiterite ore and a bituminous coal. Chemical conditions were kept constant but the water recovery was varied by changing the height of the froth column and the rate and depth of froth removed. The recovery of the floatable mineral in each system was then found to be linearly related to the weight of water recovered. The intercept of the regression line on the mineral recovery axis, where the water recovery is zero, was interpreted as the recovery due to true flotation. The entrainment contribution was proportional to the slope of the line. In this way the contributions of entrainment and true flotation to overall recovery were separated.     

The use of a new modifier,Kr6D,in differential sulphide flotation

The suitability of a new reagent, Kr6D, as a depressant for galena and sphalerite in a differential sulphide flotation stage has been tested. Small-scale laboratory flotation tests on pure sulphide minerals indicated that the reagent is capable of depressing both galena and sphalerite when used in small doses. At higher concentrations, chalcopyrite is also depressed. Single-stage batch-scale flotation tests have been carried out on bulk sulphide concentrates containing the three sulphide minerals. Kr6D has been compared with starch as a depressant both in the presence and in the absence of sulphur dioxide. In each case the new modifier has been shown to be more effective. When using sodium dichromate as a differential depressant in similar tests, it has been shown that the quantity necessary to achieve selectivity between chalcopyrite and galena may be considerably reduced if small quantities of Kr6D are added.     

ToF-SIMS-derived hydrophobicity in DTP flotation of chalcopyrite: Contact angle distributions in flotation streams

Particle hydrophobicity has been derived from Time of Flight Secondary Ion Mass Spectrometry (ToF-SIMS) measurements and its impact on the flotation behaviour of chalcopyrite investigated. Batch flotation tests were performed using a dithiophosphate-type of collector in different concentrations. Three flotation regimes were studied using particle size ranges of 20–38 μm, 75–105 μm and 150–210 μm. The individual particle contact angle, and hence, the distribution of contact angles of chalcopyrite within feed, concentrate and tail flotation samples has been determined using ToF-SIMS secondary ions. The effects of particle size and hydrophobicity on the flotation behaviour have been investigated using this new approach. The hydrodynamic effects of the particle size were highlighted by the different distributions of contact angles obtained for each concentrate size fraction, with fine and coarse sizes requiring higher average contact angles to float. This effect was overtaken by hydrophobicity when a high collector concentration was used. The broad distribution of contact angles observed in all samples, i.e. heterogeneity in hydrophobicity, has significant consequences for interpreting flotation behaviour. The methodology of analysis conducted in this study was applied to real ore and can be used as a quantitative, diagnostic tool for examining surface chemical factors affecting hydrophobicity. This new technique has promise and may advance the understanding of mechanisms, which may lead to better control strategies for improving flotation performance. Furthermore, any mineral–collector system can be targeted, provided appropriate calibration is performed.     

A compartment model for the mass transfer inside a conventional flotation cell

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.     

Modelling transport phenomena in a flotation de-inking column: Focus on gas flow,pulp and froth retention time

A laboratory flotation column using Venturi aerators and a vacuum system to remove froth was used to investigate the contribution of gas flow, pulp flow, cell volume and froth retention time on the ink removal efficiency and on cellulose fibres and mineral fillers loss. The increase in the gas flow from 4 to 8 L/min gave a general rise of particle transport from the pulp slurry to the froth with an ensuing strong increase in ink removal, from 75% to 85%, and water and total loss, from 10% to 40% and 15% to 30%, respectively. Whereas, the increase of the cell volume from 14 to 24 L improved ink removal from 72% to 80% without considerably affecting flotation loss. The rise of the froth retention time in the flotation cell from 5 to 20 s before removal gave a general decrease in the flotation loss from 20% to 11% without a corresponding decrease in ink removal. This trend was interpreted as reflecting poor ink drainage through the froth. The increase of both pulp and froth retention time in the flotation cell appeared as the most favourable way to improve ink flotation selectivity. A mathematical model, describing particle removal during flotation in terms of true flotation, entrainment and drainage, was proposed and used to fit experimental data.     

Interactive effects of the type of milling media and CuSO4 addition on the flotation performance of sulphide minerals from Merensky ore Part II: Froth stability

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 (k_t and k_w). The rate constant (k_w) calculated as a function of cumulative water recovery was used to describe characteristics of froth phase and k_t 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.     

Interactive effects of the type of milling media and copper sulphate addition on the flotation performance of sulphide minerals from Merensky ore Part I: Pulp chemistry

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.     

A laboratory study of the influence of sodium sulphide and oxygen on the collectorless flotation of chalcopyrite

The flotability of chalcopyrite in the absence of conventional collectors and its dependence on the oxidation-reduction state of the system has been determined in batch flotation tests on high-grade mineral both alone and mixed with quartz. It has been concluded that chalcopyrite is not floatable in reducing conditions either in the presence or absence of sodium sulphide but becomes floatable when oxygen is made available. No evidence was found to suggest that chalcopyrite ground in the near absence of oxygen is highly floatable.     

Exploiting the dual functions of polymer depressants in fine particle flotation

Fine hydrophilic particles are known to be entrained with water in flotation of many ores. Flocculation of the hydrophilic particles by polymer depressants could potentially reduce the mechanical entrainment of these particles. This paper reports testwork completed on fine particles of several solids, iron oxide, hydroxyapatite and sphalerite, as well as on a relatively coarse quartz sample (− 75 + 38 μm). Dodecylamine was used as a collector for quartz, and several dispersants and polymer depressants, including sodium silicate, sodium metaphosphate, zinc sulfate, cornstarch, corn dextrin and carboxymethyl celluloses (with molecular weights of both 700,000 and 80,000) were used as flotation modifiers. The major part of the testwork involved flotation tests in a 200 mL flotation column. It was observed that flocculation of the fine hydrophilic particles significantly reduced their mechanical entrainment, while dispersion severely aggravated it. Thus, in the flotation separation of synthetic mixtures of the − 75 + 38 μm quartz and fine (reagent grade) iron oxide or hydroxyapatite, polymer depressants that caused flocculation performed better than those that did not cause flocculation.     

Species interaction in flotation: A laboratory-scale semi-batch study

Semi-batch flotation tests were performed using different narrow size fractions of three different xanthate-conditioned sulphides floated singly and together in all possible combinations. To ensure proper selective flotation conditions a gangue mineral was included in all tests. Within the reproducibility of the experimentation no significant interaction among the mineral species is indicated, a result which has useful implications in distributed rate coefficient models of flotation kinetics.The conditions under which the present findings may be valid in industrial flotation are discussed, and suggestions are made for further work.     

An electrochemical investigation of pyrite flotation and depression

The oxidation of ethyl xanthate on pyrite electrodes, and the influence of the flotation depressants hydroxide, cyanide, and sulphide, have been investigated using cyclic voltammetry. A layer of a hydrated iron oxide has been identified on pyrite surfaces. Xanthate does not interact with this layer but is oxidized to dixanthogen at positive potentials. An increase in pH results in an increase in the background current due to oxidation of the mineral, and at pH=11 this reaction becomes faster than xanthate oxidation. Cyanide interacts with the electrode to form a surface species which inhibits xanthate oxidation. Sulphide gives rise to an anodic wave preceding the wave due to xanthate oxidation. The flotation and depression of pyrite are interpreted in terms of mixed-potential mechanisms.     

DAF–dissolved air flotation: Potential applications in the mining and mineral processing industry

Conventional and non-conventional flotation for mineral processing and for water (and wastewaters) treatment and reuse (or recycling) is rapidly broadening their applications in the mining field. Conventional flotation assisted with microbubbles (30–100 μm) finds application in the recovery of fine mineral particles (< 13 μm) and flotation with these fine bubbles is being used as a solid/liquid separation to remove pollutants. The injection of small bubbles to conventional coarse bubbles flotation cells usually leads to general improvements of the separation parameters, especially for the ultrafines (< 5 μm) ore particles. Results obtained are believed to occur by enhancing the capture of particles by bubbles, one of the main drawbacks in fine ore flotation. It is believed that by decreasing the bubble size distribution (through the injection of small bubbles), increases the bubble surface flux and the fines capture. DAF or dissolved air flotation with microbubbles, treating water, wastewater and domestic sewage is known for a number of years and is now gradually entering in the mining environmental area. This technology offers, in most cases, advantages over settling, filtration, precipitation, or adsorption onto natural and synthetic adsorbents. The targets are the removal of oils (emulsified or not), ions (heavy metals and anions) and the reuse or recirculation of the process waters. Advantages include better treated water quality, rapid start up, high rate operation, and a thicker sludge. New applications are found in the mining vehicles washing water treatment and reuse, AMD (acid mining drainage) neutralization and high rate solids/water separation by flotation with microbubbles. This work reviews some recent applications of the use of microbubbles to assist the recovery of very small mineral particles and for the removal of pollutants from mining wastewaters. Emphasis is given to the design features of innovative devices showing the potential of conventional and unconventional DAF flotation.     

The selective flotation of galena from sphalerite with special reference to the effects of particle size

The selectivity of galena flotation from a synthetic mixture with sphalerite and quartz and from a typical Broken Hill ore has been determined. It was found that the selectivity was limited by the relative flotabilities of coarse galena and sphalerite of intermediate sizes. The use of split conditioning in the preparation for flotation resulted in significant improvements in lead-zinc selectivity for both samples. By contrast the use of conventional zinc depressants in the flotation of the ore resulted in only slight changes in the behaviour of the minerals and had no discernible effect on the selectivity.     

新型捕收剂RA-92在低品位碳酸锰矿选矿中的应用

微细粒低品位锰矿由于颗粒间的非选择性聚集、浮选药剂用量大、浮选效率低等技术难题而致使其利用困难,造成大量浪费。在品位低于13%的锰矿浮选技术研究中,捕收剂最受关注,前人已研究了多种类型的捕收剂,所得精矿品位在16.9%~18.3%之间,回收率为56%~97%,回收率比较理想,但精矿品位总体不高。本文将新型捕收剂RA-92应用于湖南凤凰-花垣地区低品位碳酸锰矿(锰品位为10.7%)的选矿工艺中,实验研究了磨矿细度、pH值、抑制剂和捕收剂用量对浮选效果的影响,在最佳工艺条件下,精矿品位由原矿的10.7%提升至17.4%,回收率达到80.2%。研究表明RA-92对碳酸锰矿具有良好的捕收性能,浮选工艺相对简单且捕收剂用量少,浮选成本较低,可为此种捕获剂在微细粒低品位碳酸盐锰矿选矿中的应用得到推广。     

Roughing and cleaning flotation behaviour and the realistic simulation of complete plant performance

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.     

Surface chemical mechanisms of inadvertent recovery of chromite in UG2 ore flotation: Residual layer identification using statistical ToF-SIMS analysis

In the UG2 ore (Bushveld Complex, South Africa) flotation, normally more than 3% of the gangue minerals, principally chromite with talc and pyroxene, report to the concentrate diluting the PGM recovery and contributing to subsequent processing costs. Previous studies have identified residual talc-like layers on orthopyroxene surfaces in Merensky ore flotation contributing to inadvertent flotation of relatively large particles (20–150 µm) of this mineral. Chromite (75–150 µm) from flotation of UG2 ore has been similarly examined. Statistical comparison of ToF-SIMS analysis of particles from concentrate and tails reveals no significant difference in Cu, Pb, Ni and collector (IBX and DTP) signals between these streams but surface exposure of Mg and Si is favoured in the concentrate. The flotation rate of coarse chromite correlates with the exposures of magnesium and silicon in patches on the chromite surface; higher exposures give earlier flotation. Conversely, there is a negative correlation with signals corresponding to the chromite surface, i.e. Cr, Fe, Al. Flotation of chromite without collector has confirmed this statistical discrimination. Hydrophobic talc-like residual layers, similar to those found on orthopyroxene surfaces, probably from partial alteration, explain this flotation mechanism.     

Effects of an ultrasonic field on the flotation selectivity of barite from a barite-fluorite-quartz ore

The influence of an ultrasonic field frequency of 22 kHz and intensity of 0.5 W/cm² has been examined on the flotation of barite, fluorite and quartz as well as on their ability to adsorb dodecyl- and cetylsulphates. The tests affected the flotation of pure minerals in a Hallimond tube as well as the flotation of a natural barite-fluorite ore. It has been found that ultrasonic pretreatment of minerals causes an increase in the flotation rate of barite and a decrease in the flotation rate of fluorite. Ultrasonic pretreatment of the natural barite-fluorite ore before its flotation is the most advantageous. In this case it is possible to obtain concentrates of barite composed of a low amount of CaF₂. This may be explained by the different effects of ultrasonic vibrations on barite and fluorite which cause some improvement of the selectivity of their flotation separation.For a full explanation of these results the effects of ultrasonic pretreatment of the minerals on their adsorption properties and surface topography have been investigated, as well as the direct influence of ultrasound on the adsorption process.     

Sulphidizing reactions in the flotation of oxidized copper minerals,II. Role of the adsorption and oxidation of sodium sulphide in the flotation of chrysocolla and malachite

The rate of consumption of sulphide in the sulphidizing reactions of malachite and chrysocolla has been measured. The oxidation of sulphide ions at the surface of sulphidized chrysocolla was shown to take place. The influence of thiosulphate anions on the xanthate flotation of sulphidized malachite and chrysocolla was investigated and it was shown to depress the flotation of chrysocolla strongly.The result suggest, that the presence of thiosulphate as a product of simultaneous oxidation can be one of the reasons for the more difficult flotation of sulphidized chrysocolla.     

The effect of particle shape and hydrophobicity in flotation

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.     

Development and implementation of a new flowsheet for the flotation of a low grade nickel ore

Low grade nickel ores containing large amounts of serpentine minerals have historically been difficult to process efficiently. The Mt Keith ore was no exception with recoveries in the first five years of operation averaging just 60%.In this research, the factors limiting performance have been identified and a new process has been devised that raises recovery significantly. The process exploits the particle size dependence of nickel sulphide flotation and the different ways that pH change and pulp density influence the response of coarse and fine particles.Implementation of the new process at Mt Keith has raised nickel recovery by 10%. In turn, nickel production has increased by over 6000 t.p.a. and the net present value (NPV) of the operation has increased by over A$300 m. These outcomes illustrate the large commercial benefits that can be gained by understanding particle size effects in flotation.