Dynamic froth stability in froth flotation

A new measure for froth stability is introduced in this work, based on a dynamic stability test for non-overflowing froth columns. The dynamic stability factor represents the lifetime of a bubble in the froth, and is defined as the ratio of the total volume of froth at equilibrium to the volumetric gas rate introduced into the system. Experiments have been carried out at laboratory scale to measure the dynamic stability factor under different operating conditions. Air flowrate and frother concentration were the key operating variables. It was found that the equilibrium height and the dynamic stability factor depend significantly upon both the air flowrate and the frother concentration. Also, the dynamic stability factor and the fraction of air overflowing as unbroken bubbles in batch flotation tests were related and can be used to establish a stability criteria. These measurements will also allow a clearer quantitative link to be formed between froth stability with froth structure and flotation performance.     

Short-cut method for flotation rates modelling of industrial flotation banks

The knowledge of the distributed performance of a flotation bank, consisting of a number of cells in series, is a key factor for different purposes such as process design, scale-up, diagnosis, operation, control and optimization. A common practice in plant operation is to develop mass balances around the whole flotation bank in order to characterize the overall recovery, typically in rougher flotation. However, testing to fit flotation rate models are seldom developed on industrial flotation banks because they are high consumers of human labor during sampling, mineral samples preparation and chemical analysis development. In this paper a short-cut method is proposed which allows obtaining the relevant information for flotation rate modeling in a flotation bank with minimum effort and cost, and within a reasonable accuracy (less than 1–2% error in estimating cell recovery along the bank). The procedure considers two mass balances, one around the first cell of the bank and the second is the overall mass balance around the whole flotation bank, with a total of only 5 sampling streams. Examples developed in four rougher flotation banks located in three industrial concentrators illustrate the merit of this procedure.     

Case studies on the performance and characterisation of the froth phase in industrial flotation circuits

This paper deals with two separate case studies investigating the froth phase performance and characterisation of two industrial rougher/scavenger flotation circuits. Froth phase performance was quantified using a mass balance approach to estimate froth zone recovery. Measured characteristics of the froth phase included frother solution concentration determined by gas chromatography, and the time taken for an equilibrium froth sample to decay to one-half of its original froth height. The latter measurement is referred to as the ‘froth half-life’ and is strongly linked to froth stability. Special methods and techniques developed to preserve frother in solution and to measure froth half-life are briefly described. The frother type in the first case study was a mixture of straight and branched alcohols, whilst the frother type in the second case study was a mixture of alcohols, aldehydes and triethoxybutane. The first case study focussed on a flotation circuit treating a low grade ore containing only a small fraction of floatable copper sulphide minerals, while the second case study focussed on a flotation circuit treating a higher grade complex sulphide ore containing significant quantities of chalcopyrite, galena, sphalerite and pyrite.It was found that froth zone recovery of valuable mineral generally decreased down-the-bank of the two industrial rougher/scavenger circuits. Moreover, decreases in froth zone recovery significantly limit the overall cell recovery of valuable mineral achievable from the plant scavenger cells. However, the decrease in froth zone recovery could not be linked to the removal of frother from the pulp solution to the concentrate product in the preceding rougher flotation stages. Measurements of residual frother in solution suggested that, approximately, only 5–10% of the added frother was removed into the rougher/scavenger concentrate, with the remainder appearing in the scavenger tailings. This finding suggested there was apparently adequate frother in solution in the scavenger stages.There was, however, a correlation to the froth half-life, with the froth half-life also generally decreasing down-the-bank. A simple, empirical model, based on the froth half-life and froth residence time of gas, is proposed here to predict froth zone recovery. Further, it is proposed that the froth stability, as measured by the froth half-life, is strongly linked to the presence of particles in the froth, with poorly mineralised scavenger froth characterised by a short half-life and, potentially, a low froth zone recovery. The importance of particles on froth stability was confirmed in separately conducted laboratory experiments. These experiments also demonstrated the wide variation in froth stability behaviour between different frother types.     

Role of dixantogen in froth flotation

Mechanism of dixantogen action in froth flotation is discussed. It is shown that this reagent eliminates kinetic constraints during formation of a flotation complex, rather than improves hydrophobicity of a mineral surface.     

Selective detachment process in column flotation froth

The selectivity in flotation columns involving the separation of particles of varying degrees of floatability is based on differential flotation rates in the collection zone, reflux action between the froth and collection zones, and differential detachment rates in the froth zone. Using well-known theoretical models describing the separation process and experimental data, froth zone and overall flotation recovery values were quantified for particles in an anthracite coal that have a wide range of floatability potential. For highly floatable particles, froth recovery had a very minimal impact on overall recovery while the recovery of weakly floatable material was decreased substantially by reductions in froth recovery values. In addition, under carrying-capacity limiting conditions, selectivity was enhanced by the preferential detachment of the weakly floatable material. Based on this concept, highly floatable material was added directly into the froth zone when treating the anthracite coal. The enriched froth phase reduced the product ash content of the anthracite product by five absolute percentage points while maintaining a constant recovery value.     

Evaluation of the selective detachment process in flotation froth

The improved selectivity between particles of varying degrees of hydrophobicity in flotation froths has been well documented in literature, especially in the deep froths utilized in flotation columns. The phenomenon is believed to be due to the selective detachment process whereby the least hydrophobic particles are released from the bubble surface upon bubble coalescence. To quantify the selective detachment process, column flotation experiments were performed under various operating conditions that provided varying amounts of reflux between the froth and collection zones. Entrainment was eliminated by the use of relatively coarse 250 × 75 micron material. The flotation column incorporated the ability to provide instantaneous stoppage of the process streams and separation between the collection and froth zones after ensuring steady-state operation of the column. The samples collected from the two zones and process streams were evaluated to quantify the flotation rate distribution of the particles comprising each sample. The flotation rate was used as an indicator of the degree of hydrophobicity and thus a relative measure of the binding force between the particle and bubble in the froth zone. The flotation rate data was used as input into well known flotation models to obtain the froth zone recovery rate and the quantity of material that refluxes between the collection and froth zones.     

Gas dispersion measurements in industrial flotation cells

For nearly 100 years, the flotation plant metallurgist has often wondered what is happening ‘beneath the froth’. To assist in unravelling this mystery, new technology has been developed as part of the Australian Mineral Industries Research Association (AMIRA) P9 project, to measure gas dispersion characteristics (such as gas hold-up, superficial gas velocity and bubble size) in industrial flotation cells. These measurements have been conducted in a large number of cells of different types and sizes by researchers from the Julius Kruttschnitt Mineral Research Centre (JKMRC) and JKTech. A large database has been developed and the contents of this database are described in this paper.Typical cell characterization measurements show a wide spread in values, even in the same cell types and sizes performing similar duties. In conventional flotation cells, the typical gas hold-up values range from 3% to 20%, bubble sizes range between 1 and 2 mm, and superficial gas velocity ranges from 1 to 2.5 cm/s.The ranges of cell characterization measurements given in this paper will enable plant personnel to compare their operation to other similar types of operations from around Australia and the rest of the world, giving opportunities for further improvement to flotation plant operations.     

A novel approach to measure froth rheology in flotation

The current study involves a novel approach to measure froth rheology in-situ using vane. The results showed that the horizontal flow of froth towards the flotation launder interferes with the rheology measurement. A tube encircling the vane was used to minimize the effects of the horizontal flow. In order to convert the rheology raw data to rheograms, shear stress is only a function of the vane geometry and the torque values. However, it was shown that calculation of the shear rate from the vane speed depends on whether froth is fully or partially sheared.The froth characterised in this study exhibited a pseudo-plastic nature with a minor yield stress using Casson model. Therefore, froth viscosity which potentially affects froth transportation is not constant throughout the whole froth phase and it depends on the local shear rate. The suitability of the vane system to measure rheology of fluids with low shear stress was examined using a Newtonian silicone oil. It was found that the vane head should not be run in speeds above a certain range which needs to be determined. Measurements above such a speed range may not be accurate.     

煤泥浮选气泡比表面积的计算方法

为了从基于分水岭变换分割后的煤泥浮选泡沫图像上获得更加准确的气泡大小的分布情况,需要计算气泡的比表面积.由于气泡的不规则性,使用等效椭圆比等效圆来计算面积、体积更能反应真实的气泡情况.通过对比表面积进行不同的加权,比较表明,使用气泡投影的横截面积作为加权系数是描述气泡分布情况最适合的方法.同时还讨论了气泡特征与浮选操作条件之间的关系,为计算机在线控制浮选过程建立基础.     

Separation of silica from bauxite via froth flotation

This paper reports an innovative development: concentrating gibbsite via reverse froth flotation in order to obtain a metallurgical-grade bauxite concentrate. Tailings from an industrial plant have undergone attrition scrubbing and desliming; the quartz silica contained in the tailings has undergone flotation. Starch was used as a depressant, and ether-amine as the cationic collector. Optimum pH is around 10.0. In pilot plant scale, a metallurgical-grade concentrate was obtained by assaying 42.3% available alumina with an alumina/insoluble silica mass ratio of 11.1. It contained the gibbsite and the iron and titanium bearing minerals. The concentrate was further upgraded by magnetic separation, leading to 54.0% available alumina, with an alumina/insoluble silica mass ratio of 12.6 at an overall available alumina recovery of 69.3% in the final concentrate (non-magnetic product).     

硫化铜镍矿分选难点与工艺技术进展

针对硫化铜镍矿的浮选分离技术,详细总结了其选矿过程中铜镍矿物难于单体解离、含镁脉石矿物易于混杂、磨矿与分选过程溶液化学变化、铜镍分离中铜镍互含较高等技术难点,分别介绍了优先浮选、混合浮选、阶段磨浮、预先脱泥-浮选及浸出等工艺特点和应用,归纳了新型浮选药剂在硫化铜镍矿分选中的应用现状,分析了磨矿介质的类型和浮选电化学环境对浮选过程的影响,展望了硫化铜镍矿浮选技术发展趋势,指出加强磁选、生物浸出等非浮选工艺的研究能强化镍资源的回收。     

Estimation of platinum flotation grades from froth image data

Features extracted online from froth images on flotation plants are potentially useful to the development of advanced control for flotation systems, provided that these features can be related to the key indicator variables of the plant, such as valuable metal loadings and recovery. Although such relationships have been established in a number of base metal plants in industry, this is not the case in the platinum industry. In this paper, estimation of flotation grades and recoveries from froth image data is therefore considered based on laboratory and industrial plant data. It is shown that grades and recoveries can be reliably estimated from a number of different features by use of linear and nonlinear models. This includes simple colour information that on the industrial plant showed a strong correlation with grade measurement.     

The froth stability column: Measuring froth stability at an industrial scale

Froth structure and stability are known to play important roles in determining mineral flotation recovery and selectivity. However, measuring froth stability in a consistent manner remains a significant challenge, especially at an industrial scale. Following preliminary tests on a copper concentration plant, a quantitative dynamic stability measure is investigated in this study in order to extend the results over a wider range of conditions and on a different ore body. The technique is based on the Bikerman foam test and uses a non-overflowing froth column to quantify froth stability.Experiments were carried out using an automated version of the froth stability column under different operating conditions. Air flowrate was the key operating variable. Tests were reproduced on a single flotation cell of a Platinum Group Metals concentrator. The froth stability factor, β, was measured for each operating condition, and compared with the air recovery in the cell, α, which was measured using image analysis. The froth stability column results gave the same trends as image analysis. In particular the froth stability factor was found to be linearly related to the actual fraction of air overflowing the cell.The metallurgical results clearly indicated that changes in air flowrate result in variations in flotation performance that can be attributed to changes in froth stability. The results showed that high froth stability conditions occur at intermediate air flowrates, and result in improved flotation performance. It is found that the froth stability column is a simple, cost-effective and reliable method for quantifying froth stability, and for indicating changes in flotation performance.     

降低浮选泡沫稳定性的探索试验

针对浮选生产中浮选泡沫过于稳定而困扰生产的问题,研究采用分步释放浮选试验结果来判断泡沫的稳定性,以煤粒粘附百分比来定量分析判断泡沫的稳定性。试验结果表明,当煤油作为捕收剂时,浮选泡沫稳定性小于轻柴油。林西选煤厂浮选入料的单元浮选试验表明:煤油、轻柴油或者两者以不同比例掺混,其浮选效果无显著性差别,从而为生产中降低浮选泡沫稳定性提供了参考。     

XJQM-14型浮选机刮泡装置技术改造

分析了XJQM-14型浮选机刮泡装置频繁出现故障的原因,重点介绍了改造刮泡装置,并指出改进后减少了事故及维修量,取得了明显效果。     

CFD modelling of bubble–particle attachments in flotation cells

In recent years, computational fluid dynamic (CFD) modelling of mechanically stirred flotation cells has been used to study the complexity of the flow within the cells. In CFD modelling, the flotation cell is discretized into individual finite volumes where local values of flow properties are calculated. The flotation effect is studied as three sub-processes including collision, attachment and detachment. In the present work, these sub-processes are modelled in a laboratory flotation cell. The flotation kinetics involving a population balance for particles in a semi-batch process has been developed.From turbulent collision models, the local rates of bubble–particle encounters have been estimated from the local turbulent velocities. The probabilities of collision, adhesion and stabilization have been calculated at each location in the flotation cell. The net rate of attachment, after accounting for detachments, has been used in the kinetic model involving transient CFD simulations with removal of bubble–particle aggregates to the froth layer.Comparison of the predicted fraction of particles remaining in the cell and the fraction of free particles to the total number of particles remaining in the cell indicates that the particle recovery rate to the pulp–froth interface is much slower than the net attachment rates. For the case studied, the results indicate that the bubbles are loaded with particles quite quickly, and that the bubble surface area flux is the limiting factor in the recovery rate at the froth interface. This explains why the relationship between flotation rate and bubble surface area flux is generally used as a criterion for designing flotation cells. The predicted flotation rate constants also indicate that fine and large particles do not float as well as intermediate sized particles of 120–240 μm range. This is consistent with the flotation recovery generally observed in flotation practice. The magnitude of the flotation rate constants obtained by CFD modelling indicates that transport rates of the bubble–particle aggregates to the froth layer contribute quite significantly to the overall flotation rate and this is likely to be the case especially in plant-scale equipment.     

煤泥浮选泡沫特征提取算法综述

介绍了浮选泡沫表面的物理特征、纹理特征和动态特征提取的主流算法,分析了各算法的优缺点,对解决现阶段人为判别泡沫状态比较困难的问题,实现浮选自动化,提高浮选工艺指标具有一定的指导意义。     

Influence of coal particles on froth stability and flotation performance

Solid particles have significant effect on flotation froth. In this research, the effects of coal particles of different size and hydrophobicity on froth stability and flotation performance were studied. The froth stability was measured in both the froth formation and froth decay processes by maximum froth height, froth half-life time and water recovery. The results show that fine particles of moderate hydrophobicity contributed most to maximum froth height in the froth formation process and were most favorable for flotation. Fine hydrophilic particles stabilized the froth in the froth formation process but the froth half-life time was very short due to the high water solid ratio. High hydrophobic particles of both fine and coarse size fractions greatly increased the froth half-life time in the froth decay process. But the froths were very rigid and the maximum froth heights were very low. The presence of fine hydrophobic particles was very unfavorable for the recovery of coarse particles.