Molecular modelling of reagents for flotation processes

It has long been recognized that the selectivity of froth flotation processes is highly influenced by the specificity of interactions between minerals and reagents that are used to control the hydrophobic/hydrophilic character of the mineral/water interfaces. We have modelled mineral surfaces (hydroxy-apatite, calcite) and molecules of two polysaccharides (starch, ethyl-cellulose) which are candidates as depressing agents for calcite. A special parameter named “Total Fitting Number” (Ft) was developed to assess the steric compatibility between the structure of both minerals and polysaccharide species. The calculation of Ft was based on measurements of OH-OH distances that exist at reagent molecular structures versus Ca---Ca distances that exist along the most common crystallographic orientations (hkl) exhibited by mineral particles.Higher values of Ft were found for the interaction calcite/starch than calcite/ethyl-cellulose. This finding suggests that starch is a more effective depressant for calcite than ethyl-cellulose. However, low values of Ft were found for the interaction apatite/starch and apatite/ethyl-cellulose. This fact means that both substances are unlikely to act as depressants for apatite. Microflotation response of apatite and calcite with sodium oleate (pH = 10.2) in the presence of both polysaccharides corroborates the model.     

Troubleshooting industrial flotation columns

Since the early 1980s flotation columns have been progressively incorporated in milling operations all over the world. Improvements in final concentrate grade, using single cleaning stages, have been in most cases the reason for using this new technology. However, the main disadvantage with respect to conventional mechanical cells is the large spread of'results, mainly in terms of recovery, which is normally compensated by a high circulating load and high capacities (overdesign).Besides normal changes in feed grade and flowrate, and the need for periodic maintenance for gas spargers, the following common troubles in plant practice are discussed: . improper calibration and maintenance of instrumentation to measure froth depth and gas rate . bias definition and estimation . uneven wash water distribution . uneven froth depth in baffled columns . lack of robustness of control strategiesProper boundaries for superficial wash water rate (0.1–0.2 cm/s), froth depth (0.5–1.0 m) and superficial gas rate (I-2 cm/s), based on fundamental knowledge and experience in large size columns, are suggested for stable operation. Unfortunately, the lack of coordination between these variables is an important limitation for metallurgical improvements.The effect of altitude on gas rate and gas holdup in flotation columns operating at 1500–4500 m over the sea level is analysed.     

Collection zone kinetic model for industrial flotation columns

The collection zone recovery of a flotation column was modeled using a rectangular distribution function for the kinetic rate constant and a tank in series model with different vessel sizes for the residence time distribution. It was demonstrated that an analytical expression can be obtained and that data from large industrial columns fits well, keeping the parsimony principle by using a simple and practical solution. An example for the estimation of the maximum kinetic rate constant, useful for scale-up purposes, is shown using data from industrial flotation columns.     

Geometallurgical modelling of the Collahuasi flotation circuit

The flotation rate constant was modelled as a function of air dispersion properties and the complete feed particle size distribution by using the collision–attachment–detachment approach and introducing a parameter (Ф) which represents the inherent floatability of the ore. It was found that this parameter Ф is characteristic of the geometallurgical unit and does not depend on the main operating conditions. The parameter Ф is dimensionless and can be estimated either from laboratory testwork or directly from an industrial kinetics survey and can be used to predict industrial operation, provided that the other components of the model are evaluated under actual operation conditions. An empirical expression for the maximum achievable recovery – infinite time recovery – is also presented. The complete model, including flotation rate constant and infinite time recovery, was tested showing good correlation at both laboratory and industrial scale. At industrial scale the model was able to predict metallurgical results in a time frame of several weeks at Compañia Minera Doña Inés de Collahuasi SCM, showing an average relative error of less than 2%.     

On the collection of valuable minerals along rougher flotation banks

The collection of valuable minerals along rougher flotation banks was evaluated using top-of-froth measurements, which consist of sampling the froth surface. Considering non-selective froths observed in rougher flotation circuits, it was found the top-of-froth grades were similar to the bubble load grades, which allowed for a direct estimation of the collected mineral characteristics (size distribution, mineralogy, and grade). Thus, the flotation process evolution can be characterized by analyzing the collection of valuable minerals by true flotation instead of the classical mass balances approach, which strongly depends on the reliability of the tailings grade data. In addition, comparison among different valuable minerals was observed without significant sampling disturbances caused by solid entrainment.It is expected the top-of-froth measurement will be a useful tool for evaluating the effect of operating variables such as pulp conditioning, air flowrate and solids percentage on the true collection process along a flotation bank.     

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.     

非碱性浮铜新工艺工业试验研究

广东某大型铜硫矿矿石富含磁黄铁矿型铜硫矿和黄铁矿型铜硫矿,因露天开采,矿物表面易氧化.采用常规的强碱浮铜工艺,生产指标波动较大.对此,研究开发出非碱性浮铜工艺,即在铜粗选中加少量石灰调矿浆pH=7左右,同时加入特效调整剂CW.在原矿中磁黄铁矿与黄铁矿的比例以及黄铁矿型氧化矿含量不同的情况下,获得较好的工业试验指标:铜精矿Cu品位19.59%~24.12%、铜回收率83.03%~85.91%,硫精矿S品位37.86%~40.46%、磁硫精矿S品位30.02%~32.89%,总硫回收率90.14%~93.12%.     

Froth recovery measurements in an industrial flotation cell

The froth phase serves an important role in upgrading the final concentrate in flotation. At present, the techniques that are used in the mineral industry to determine the effect of froth phase on the metallurgical performance of plant scale flotation cells have limitations.The aim of this paper is to investigate the performance of the froth in an industrial flotation cell. A unique device has been developed which is able to decouple the froth zone from the pulp zone. The device consists of two concentric tubes. The inner tube acts as a dropback collection chamber or catcher. The particles that return from the froth phase fall directly into the catcher and are collected as froth dropback. This technique is capable of measuring plant scale flotation cell froth recovery as well as providing valuable information on froth dropback particles.The froth recovery measurements were carried out in a rougher bank of a copper concentrator treating sulphide minerals. The dropback device is designed so that it can be immersed into an industrial size flotation cell and plant froth recovery measurements can be taken at any given location. During the experiments, the bubbles laden with valuable mineral particles entered the device from the flotation cell, subsequently rising to form a froth layer at the top of the device. The particles that detached or drained from the froth zone were collected in the dropback collection chamber whereas the concentrate sample was collected through a launder. By sizing and chemical analysis of the concentrate and dropback samples, the froth recovery was estimated on the basis of the valuable component. The effect of air rate on the froth recovery was also investigated. Metallurgical grades of the froth dropback device samples for different particle size ranges were compared to those of the concentrator to better understand the froth dropback mechanism.     

Sampling and flotation testing of Sudbury Basin drill core for process mineralogy modelling

The area of flotation testing of drill core is important in the business plan of most mining companies. Metallurgical information derived from this practice can be used to advantage in strategic decision-making. Sampling, flotation testing and subsequent QemSCAN (Quantitative Evaluation of Minerals by Scanning Electron Microscopy) analysis of a mineral resource is one example of this approach. A new resource, located in Sudbury, Ontario, is being assessed for the Sudbury Operations of Falconbridge Limited, which includes the Strathcona Mill.In this case, it was possible to improve the value of information from sampling and flotation testwork by using an improved, statistically-based test design, by sampling the resource by generic end-member ore type, and by integrating the Mineral Processing and Mineral Science disciplines into a Process Mineralogy team. In addition to producing standard metal grade and recovery information, this new approach provides more reproducible information from representative samples and flotation testing in a replicate format. QemSCAN technology is used to produce a size by size mineral balance, including both modal percentages and liberation, from which flotation models for each ore type can be developed. As a result, a key understanding of the potential behaviour of a given ore type, if mined and then processed at the current mill operation, is gained at the 95% confidence level.The three ore types of this mineral resource were shown to have different flotation characteristics. Quantifying the mineralogy and liberation in each of the three ore types, has shown that this difference is due to changes in modal percentages of ferro-magnesium and magnesium silicate minerals such as pyroxene, talc and serpentine. Liberation across the three ore types is very similar and is therefore not responsible for variation in flotation performance.     

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.     

细粒锡石浮选的试验研究和工业化应用

对云南某选矿厂硫化矿系统的泥化矿进行了选矿试验研究,通过旋流器脱泥、浮选除硫、锡石浮选的工艺,从锡品位为0.380%的给矿中获得了品位和回收率分别为8.47%和43.10%的锡精矿,锡石浮选作业回收率为78.13%。工业生产试验取得了与室内试验较为接近的指标,其结果进一步证明了锡石浮选工艺处理此类细粒级锡石具有明显的优势。     

GAS holdup and RTD measurement in an industrial flotation cell

In this work, the measurement of the axial gas holdup profile and gas residence time distribution (RTD), in a 130 m³ self-aerated flotation cell, is presented. For this purpose, a radioactive tracer gas was activated in the Nuclear Reactor of the Chilean Commission of Nuclear Energy.The gas tracer, Freon 13B1, was injected as an impulse signal at the gas (air) inlet point, located at the top of the cell, from which the gas tracer circulates first through the rotor, where the bubble dispersion occurs, and then the gas becomes well distributed over the whole cross-sectional area before leaving the cell.The axial gas holdup profile was estimated from the transient gas concentration measurement at different depths inside the cell. From these experiments it was found that the air entering the cell was preferentially distributed in the upper half of the cell, while the gas entrainment into tailings was negligible. The mean gas holdup was 8.8%, and consequently the effective pulp volume of collection zone was 91.2%.The gas concentration on top of froth was recorded for RTD measurement of the gas leaving the cell. It was found that the mean gas residence time was around 42 s and the mixing condition for gas and pulp was similar.     

Froth zone characterization of an industrial flotation column in rougher circuit

In this investigation the froth zone of an industrial column (4 m “diameter” × 12 m “height”) in rougher circuit was characterized. Experiments were carried out at Miduk copper concentrator, Iran. Miduk is a unique copper processing plant which utilizes columns in rougher circuit. Cleaning and selectivity actions in the rougher froth were illustrated using solids and grade profiles along with RTD data. The impact of froth depth (FD) on overall rate constant (k) and k–S_b relationship was evaluated. Dependency of overall flotation kinetics on froth depth and gas velocity (J_g) was modeled by k = 4.97(FD)^?0.87(J_g)^0.80. Froth recovery (R_f) was estimated and modeled in terms of froth residence time of slurry (FRT_Slurry) as R_f = R_f,maxexp(?k × FRT_Slurry). Finally, the correlation between k, S_b (indicative of the collection zone performance) and FRT_Slurry (indicative of the froth zone performance) was modeled by k = 0.02 (FRT_Slurry)^?0.62(S_b)^0.82.     

会泽铅锌硫化矿浮游性评价新方法

采用分批刮泡浮选试验方法,根据模糊数学中的隶属度和隶属函数,提出从可浮性和浮游速度两个方面综合评价矿物浮游性的新方法,实现了矿物浮游性的量化。应用新方法分析了会泽方铅矿、闪锌矿和黄铁矿在矿浆pH值为7.5,乙基钾黄药浓度为2.0×10-4 mol/L,硫酸锌浓度为1.5×10-4 mol/L条件下的浮游性,结果表明3种矿物的浮游性依次是方铅矿>黄铁矿>>闪锌矿,这与浮选工业实践中的结果相符合。     

工业浮选柱的气含率测定及其影响因素研究

气含率是影响浮选柱分选效果的重要参数之一。采用压差法测定浮选柱内部的气含率,并基于直接数字控制(DDC)技术和MCGS组态软件,设计开发了适合于工业浮选柱的气含率测试系统。通过对循环压力、充气量和起泡剂用量3个因素进行试验,研究了它们对工业浮选柱气含率的影响。结果表明:循环压力、充气量和起泡剂用量对气含率影响显著;在一定范围内气含率随着循环压力、充气量和起泡剂用量增大而增大,当增大到一定程度时气含率增大的幅度逐渐减小。     

Sequential multi-scale modelling of mineral processing operations,with application to flotation cells

Processing of minerals and metals involves phenomena functioning over a wide range of length scales. Equipment is generally large in order to process the required large flow rates, yet achieving the functional requirements of the operation requires successful execution of micro-scale processes. Multi-scale modelling approaches to process simulation are firstly reviewed, and similarities and differences compared with the more common multi-scale approaches to materials modelling are given.The sequential multi-scale method is then illustrated with reference to the mineral flotation process. In this case, multi-phase CFD (computational fluid dynamics) models of large-scale cells has been complemented by micro-scale CFD simulations of bubble–particle collision, and experimental and modelling studies of the bubble–particle attachment process itself.Finally, other examples of sequential multi-scale modelling are summarised, highlighting progress on unit operations including aluminium reduction cells, leaching heaps, copper solvent-extraction settlers, and fluidised beds.