Variation of flotation rate coefficients in zinc cleaning circuits

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.     

Effects of Particle Size and Chain Length on Flotation and Adsorption of Quaternary Ammonium Salts onto Kaolinite

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.     

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.     

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.     

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.     

A rational interpretation of the role of particle size in flotation

From the examination of data from detailed plant surveys and associated laboratory batch testing, the principal effects of particle size in flotation have been identified. The current state of knowledge concerning the role of this variable is discussed in terms of the evidence presented. It is concluded that the minimum degree of hydrophobicity necessary for the flotation of a particle depends upon its size and as a result, recovery-size curves are a valuable diagnostic aid to the assessment of flotation performance. Entrainment is shown to be an important contributory mechanism to the recovery of fine particles which, when coupled with a low rate of genuine flotation, can account for much of the observed behaviour of such fines. The significance of particle size and its consequences in flotation research, in plant operations and in control schemes has been under-rated. The separate conditioning or flotation or both of separate size fractions seems inevitable as ores become increasingly difficult to concentrate.     

An analysis of the dynamic characteristics of flotation circuits by time-series analysis

Time-series analysis techniques are used to investigate the dynamic characteristics of the flotation circuits on the Renison tin concentrator in Tasmania. Routine plant-operating data provide information on the variability of feed streams, the disturbances resulting from normal manual operation, the suitability of certain locations for sitting instruments, and some simple time delays in the circuit. It is also shown how plant upsets and abnormal conditions caused by large perturbations to the operation can prove useful in such studies. Finally, a dynamic experiment is described which shows that disturbances higher in frequency than those in the feed are induced in the roughing and scavenging operations, but that these are filtered out again in the cleaner circuit. The uses and limitations of these techniques are discussed.     

The natural flotability of chalcopyrite

In an extensive programme of batch flotation tests on mixtures of purified minerals, it was established that freshly ground chalcopyrite displayed natural flotability in an oxidising environment and non-flotability in a reducing environment. No rational hypothesis to account for this behaviour has emerged. Grinding in an iron mill produced strongly reducing conditions and consequently suppressed flotation which was restored subsequently by raising the potential of the pulp either by aeration or by the addition of oxidants. The coarse particle sizes recovered more slowly than other fractions. The type and addition of frother had a pronouced effect on the natural flotability, but no proven effect on hydrophobicity. There is some evidence that whilst these observations apply to chalcopyrite from several sources when floated from mixtures with quartz, chalcopyrite in real ore samples does not necessarily show the same flotation behaviour.     

Effect of collector, pH and ionic strength on the cationic flotation of kaolinite

The effect of amine collector type, pH, and ionic strength on the flotation behaviour of kaolinite was investigated in a series of laboratory batch flotation tests. In distilled water, ether diamine, a strong collector for silica, does not induce any flotation or only very weak flotation of kaolinite over a wide pH range from pH 3 to pH 10.5. Ether monoamine causes strong flotation of kaolinite in distilled water, especially in acidic solutions, but high dosages of the collector are required. Such observations are in contrast to the flotation behaviour of oxide minerals such as silica for which ether diamine shows stronger collecting power than ether monoamine. The pH dependence of kaolinite flotation is also opposite to that of oxides, with lower flotation recovery obtained at higher pH. In contrast to oxides, the flotation recovery of kaolinite increases with ionic strength. It was demonstrated that the enhanced flotation of kaolinite in NaCl solutions cannot be attributed to the frothing ability of NaCl or the intercalation of kaolinite by alkylamines. It is proposed that the screened zeta potential of kaolinite particles in a high ionic strength environment causes random aggregation of kaolinite particles exposing hydrophobic (001) silica plane in the presence of ether amines.     

Micromechanical Modelling of Granular Materials: Effect of Particle Size and Gradation

In this paper the effects of maximum particle size, particle gradation/sorting and fabric on bulk mechanical behaviour of granular materials such as coarse grained soils and rockfills are investigated" from micromechanical considerations starting from the grain scale level, using numerical" simulations based on Discrete Element Modelling (DEM). Hydrostatic compaction and biaxial tests on 2-dimensional assemblies of discs with varying particle sizes and gradations were modelled using DEM. An examination of the constitutive behaviour of granular media considering" the particulate nature of the medium has been attempted to explain the effect of particle size and gradation. Simulation results on perfectly parallel graded assemblies indicate that with increase in the size of the particles, a marginal increase (or no increase) in the angle of internal friction is observed during biaxial loading conditions. A change to a wider gradation (keeping the minimum grain size the same) results in a decrease in the angle of internal friction and an increase in volumetric strain to a considerable extent. Based on micromechanical force and fabric parameters, the basis for the physical behaviour was established. This helps in understanding the physics of parallel gradation techniques.     

Flotation circuits for poorly floating coals

A number of flotation circuits for the recovery of a poorly floating coal were investigated by laboratory batch testing. Analysis of the size and ash distributions of the products and tailings showed that the circuits which would allow an equitable distribution of collector between the coarse and fine size fractions were superior. These circuits were two-stage reagent addition, reflotation of classified tailings and split feed flotation. The reflotation of classified tailings circuit not only gave the best metallurgical performance, it also was the least affected by pulp density variations and imperfect size classification.     

Electro-flotation of chalcopyrite fines

Electro-flotation tests were conducted on chalcopyrite particles with a modified Hallimond tube designed for electro-flotation, using platinum anode—copper cathode and graphite anode—copper cathode systems. Flotation tests were carried out for fines of chalcopyrite of size below 20 microns with potassium ethylxanthate as collector. Studies were done on flotation with hydrogen and oxygen separately with the usual variables. Dissolution of chalcopyrite at various current densities, with reagent at optimum conditions and without reagent was also studied. It is observed that electro-flotation particularly with oxygen, is effective in the flotation of fine particles of chalcopyrite.     

The air flow number in flotation machine scale-up

The flotation cell is quantified as a mixing device for one, two, and three phase systems using combinations of water, air, and solids. To do this, power consumption was measured as a function of impeller speed, rate of aeration, and solids concentration. Initial suspension of solids and dispersion of suspended solids throughout the water or water/air system were also studied as influenced by impeller speed, particle size and solids concentration. The power number and air flow number were used to correlate the data.Flotation studies with a zinc ore using three sizes of cells of the same design, showed that aeration had to be controlled in the smaller cells to duplicate the results in the cell of commercial size. For optimum results the flow number range in the smallest cell was less than the critical value for suspension of coarse particles. Operating flow numbers for the three cell sizes under optimum conditions were close; commercial cells of the same size operating elsewhere appear to have two to three times higher flow numbers.The general relationships among air flow, impeller speed, particle suspension and flotation are discussed with particular reference to scale-up problems and coarse particle flotation. Both impeller speed and aeration should be considered as variables requiring systematic study and independent adjustment.     

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.     

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.     

钙质粗粒料颗粒强度和压缩特性的试验研究

目前对钙质土压缩特性的研究主要集中在钙质细砂,而实际工程中广泛存在钙质粗粒料,因此对钙质粗粒料压缩特性开展研究具有重要意义。通过颗粒强度测定仪和全自动大型固结仪对钙质土进行了单颗粒破碎试验和一维压缩试验,研究了颗粒粒径和相对密度对钙质粗粒料的颗粒强度和压缩特性的影响。单颗粒试验结果表明,钙质砂单颗粒的特征应力随着颗粒相对密度的增大而增大;单颗粒的破碎强度具有明显的尺寸效应,可利用单颗粒的特征应力进行标准化,且服从Weibull分布。压缩试验结果表明,单一粒径试样破碎后的分形维数随颗粒粒径的增大而增大;试样的Hardin破碎率与塑性功的关系为幂函数关系;在本次试验条件下,单一粒径试样的屈服应力与单颗粒的特征应力存在近似线性关系。     

The effect of air flow rate on the kinetics of flotation. Part 1: The transfer of material from the slurry to the froth

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.     

The Comprehensive Utilization and Purified Research on Kaolin Ores in Huichang

Kaolin ores in Huichang contains these minerals of quartz sand, kaolin, mica and feldspars. In order to recover these valuable resources, some experiments of screening, classification, magnetic separation, grinding and flotation are carried out on the basis of the kaolin ore properties. The test results indicate that quartz sand concentrate can be directly obtained when vibrating screen size used is 10 meshes. Materials that are smaller than the screen hole are injected to hydraulic cyclones which controlling classification size is 325 meshes; kaolin concentrate containing above 33.70% Al2O3 and 0.37% Fe2O3 can be well beneficiated from the overflow through magnetic separation with one stage rougher and cleaner to remove iron. On the other hand, the hydrocyclone spigot flow to grinding and flotation with one stage rougher and two scavengers, mica and feldspars concentrate can be beneficiated in sequence. Therefore, these valuable minerals of kaolin ores can be realized comprehensive utilization.     

Particle transport within water-saturated porous media: Effect of pore size on retention kinetics and size selection

The transport and filtration behaviour of fine particles (silt) in columns packed with sand was investigated under saturated conditions by using step-input injections. Three samples of different particle size distributions (coarse medium, fine medium and a mixture of both) were used in order to highlight the influence of the pore size distribution on particle retention and size selection of recovered particles. The main parameters of particle transport and deposition were derived from the adjustment of the experimental breakthrough curves by an analytical model. The higher particle retention occurs in the mixture medium, owing to its large pore size distribution, and the filtration coefficient decreases with increasing flow velocity. Particle size distribution of recovered particles shows a thorough size selection: (i) the first recovered particles are the coarser ones; (ii) the size of the recovered particles increases with increasing flow velocity and enlarger pore distribution of the medium.