Simultaneous determination of collection zone rate constant and froth zone recovery in a mechanical flotation environment

This paper presents the results of an investigation in which the new JKMRC Flotation Cell was used to determine the collection zone rate constant and froth zone recovery of a copper rougher ore simultaneously.The determination of these two parameters has been based on the straight line relationship that exists between the overall flotation rate constant and the froth depth [1].Experimental work was conducted using a copper rougher ore with a P₈₀ of 200 μm. Operating variables such as air flow rate, impeller speed, feed percent solids, collector and frother dose, and wash water flow rate were investigated. Analysis for copper and iron minerals (chalcopyrite and pyrite, respectively) was carried out.The results indicate that the collection zone rate constant of both copper and iron minerals increased with increasing air flow. Froth zone recovery, on the other hand, decreased as air flow was increased, possibly as a result of increased detachment of particles from bubbles in the froth. Increasing the impeller speed also increased collection zone rate constant and decreased the froth zone recovery of both minerals.Experiments at different wash water flow rates have showed that events occurring in the froth zone do not affect the kinetics of the pulp zone. Moreover, and interestingly, the froth recovery of attached particles (wash water reduced entrainment to a minimum) was non-selective. The froth recovery curves for chalcopyrite and pyrite followed each other very closely in every instance studied.The work has proved that it is possible to measure both the collection zone rate constant and froth zone recovery simultaneously and continuously in a mechanical flotation environment. The results obtained to date are interesting and the work is continuing.     

The development of a cavern model for mechanical flotation cells

Certain fine particle and high solid concentration mineral slurries used in the froth flotation process have been shown to exhibit non-Newtonian rheologies, including a yield stress. The mixing characteristics of these fluids are often problematic as a cavern of yielded fluid forms around the impeller whilst the rest of the fluid remains stagnant and therefore unmixed. This paper aims to develop a semi-empirical model to calculate the height of caverns forming in non-Newtonian mineral slurries in a mechanical flotation cell.Cavern shapes in a pilot-scale Batequip flotation cell were numerically determined for a range of mineral slurries using an experimentally validated Computational Fluid Dynamics (CFD) model. Development of the cavern height model was based on the assumption that the cavern boundary was formed where the shear stress imposed on the slurry equaled the fluid yield stress and also that the flow along the cell walls could be represented by an annular wall jet. It was found that the cavern height was directly proportional to the product of the slurry density and the square of the impeller tip speed, and inversely proportional to the slurry yield stress.     

基于裂纹的岩石摩擦滑移位移演化实验研究

为研究岩石破坏形成断裂面或结构面后的进一步演化特征,选用一种花岗岩制备了双穿透裂纹试件,采用双剪模型开展了摩擦滑移试验研究。用CCD相机记录试验过程中的散斑图像,并利用数字散斑相关方法对岩石摩擦滑移过程中的水平位移场、竖直位移及水平位移的演化特征进行分析。结果表明:①剪应力缓慢增长阶段的位移演化,由围压起主要作用转变为围压和剪切力共同作用,线性增长阶段则以剪切力作用为主;界面咬合程度及水平错动位移的增减变化可作为界面摩擦滑移的前兆;②水平位移场绕流现象的出现和消失,分别是试件局部和整体滑移的前兆;③位移场云图中部等值线的倾斜角度可表征围压与剪应力的关系,也可作为试件局部和整体滑移的前兆。     

The relationship between the peak in air recovery and flotation bank performance

Air recovery, or the fraction of air entering a cell that overflows the cell lip as unburst bubbles, is an important measure of froth stability as it affects the flow of bubble surface to the concentrate. An experimental campaign was carried out over the first four cells of the rougher bank at a South African platinum mine in order to find the relationship between froth stability and flotation performance as a function of air flowrate.The results showed that a peak in air recovery was observed as the air rate increased. Furthermore, this corresponded to the air flowrate at which the highest overall recovery was obtained. This can be explained by understanding the resulting changes in the structural features of the froth such as bubble loading and the flow of bubble surface and suggests that improved flotation performance can be achieved by operating a bank under conditions that result in a maximum in froth stability.     

Behaviour of swelling clays versus non-swelling clays in flotation

The deleterious effects of clays on flotation performance are widely acknowledged but the mechanisms involved are not clearly established. Moreover, the concentrations beyond which clay minerals become problematic are not clearly defined. One major parameter is the difference between swelling and non-swelling clays which is evaluated in this study. The ore slurry pulp rheology and froth stability were monitored in the absence and presence of different clay minerals. It was found that swelling clays can adversely affect the flotation performance mainly via adsorbing water which changes the rheology and froth stability, reducing both flotation grade and recovery. Non-swelling clays had a lower effect on the rheology. Kaolinite increases the froth stability and reduces the flotation grade but illite showed the least effect on the flotation performance in this study. The potential mechanisms and critical concentrations are discussed.     

The effect of mothers on bubble size distributions in flotation pulp phases and surface froths

Froth dynamics, i.e. the stability and mobility of the froth, are crucial indicators of various important features of flotation systems. For example, it is desirable that the froth collapses as soon as possible after it is skimmed off the cell in order to curtail losses in throughput. On the other hand, if the froth is too prone to collapse, it will not be sufficiently stable to support its load prior to skimming. Likewise, the mobility of the froth gives similar information on the performance of the flotation cell. For example, a sharp contrast can be observed between dry viscous (immobile) froths and watery runny froths with high mobility. Several authors have recently shown that analysis of the structure of the froth in a flotation cell can be used to assess the performance of the cell. This implies that there is a close relationship between the bubble size distribution in the pulp and froth phases.Until very recently, it was not possible to verify this hypothesis direct, since reliable measurements of bubble size distributions in especially the froth phase could not be obtained. With recent improvements in the machine vision technology originally developed at the University of Stellenbosch, it is now possible to measure bubble size distributions and stability in froth structure with a high degree of accuracy. Unlike previous methods, these improved algorithms can provide a detailed map of flow patterns in the froths, which can give a significantly better idea of operating conditions in the flotation cell. Consequently, in this experimental study the bubble size distribution in the pulp phase of a laboratory flotation cell was measurement with a capillary tube system (UCT bubble size analyser), while the bubble size distribution in the froth phase was measured by use of digital image analysis. The relationship between these bubble size distributions in the pulp and froth phases is discussed.     

基于颗粒流理论的深海沉积物剪切特性模拟研究

基于深海沉积物的微观物理性质, 提出以膨润土、硅藻土和水等物料为主成分的模拟沉积物配方, 配制了与深海沉积物相似的模拟沉积物, 并开展其十字板剪切实验, 从宏观上获得其应力-转角的剪切特性曲线。基于颗粒流理论, 采用接触粘结模型, 构建了具有高孔隙比、高含水率和粘聚力等特性的沉积物颗粒流模型, 开展其十字板剪切过程数值模拟, 从细观上获得其应力-转角的剪切特性曲线。研究表明, 模拟沉积物具有与深海沉积物相同的极低剪切强度和剪切变稀特性, 其剪切特性的细观数值模拟曲线与宏观实验曲线吻合, 验证了粘性的沉积物颗粒流模型和数值模拟方法的正确性, 探明了沉积物颗粒的细观参数, 表明粘结强度决定沉积物宏观的剪切强度, 为海底采矿车行走性能实验和从细观层面研究深海沉积物剪切特性提供了坚实基础。     

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.     

基于极限树回归的浮选泡沫层厚度预测研究

泡沫浮选是一种重要的选矿方法，不同表面物理化学性质的矿物颗粒在药剂的作用下借助浮选机实现分离。浮选机的控制变量包括充气量、泡沫层厚度和药剂添加量等。泡沫层厚度是影响浮选指标的一个重要控制参数，同样，泡沫层厚度的准确测量也至关重要。传统的泡沫层厚度测量方式一般是采用传感器等装置来实现的，由于这些传感器往往需要与矿浆直接接触，所以有时会因机械故障或信号干扰而造成测量值的误差。 针对传统测量手段存在的问题，本文提出了一种浮选泡沫层厚度的软测量方法。运用极限树回归ETR方法，以浮选过程中原矿品位、入料流量、入料浓度、入料粒度、充气量、泡沫稳定度和泡沫移动速度为输入变量，建立预测模型，实现了浮选泡沫层厚度的有效预测。     

Relationship between the bubble surface flux that overflows and the mass flow rate of solids in the concentrate of flotation processes

This paper presents the relationship between the bubble surface flux that overflows and the mass flow rate of solids in the concentrate. Even though this study was carried out in a flotation column, the knowledge derived from this paper may be applied to all froth flotation processes. The experimental set up was equipped with an image analysis system to estimate the froth bubble diameter and the air recovery. This study describes the difference between the bubble surface flux entering the froth zone (S_bI) and the flux that arrives to the top of the froth (S_bT) and then overflows to the concentrate (S_bO), the latter being most directly related to the mass flow rate of solids in the concentrate. It was observed that the superficial area of the overflow increased with increasing collector addition and air flow rate, but decreased with increasing froth depth and particle size distribution. Visual evidence and experimental results suggest that, it is common that the superficial area of air that overflows in the concentrate is covered by particles. Only when this condition is almost achieved does overflows occur; otherwise, a high level of coalescence and bubble bursting take place at the froth surface. This was concluded after finding compatible trends between the estimated and predicted mass flow rates of solids in the concentrate, when a tractable geometrical model was used (R² = 0.8).     

Determination of ferrosilicon medium rheology and stability

Ferrosilicon (FeSi) has a fast settling rate in dense suspension, attributed to its very high solids density, coarse particle size, more spherical particle shape and low medium viscosity. The fast-settling nature in dense suspension is a challenge to acquire reliable rheological data. A testing rig was set up to maintain a constant medium density during the rheology measurement by circulating the medium to keep FeSi particles well suspended. A rotational rheometer with a modified concentric bob-cup measuring system was incorporated in the testing rig. Taylor number (T_a) was calculated and a threshold T_a = 41.3 was used to identify the onset of unstable laminar flow owning to the Taylor vortices and turbulence formation in the measuring system. The data with T_a > 41.3 were excluded in the determination of rheological flow curves. Evaluation of the modified measuring system with Newtonian silicone oils of known viscosities confirmed that the system can produce true flow curves over the entire tested shear rate range for a stable laminar flow (T_a < 41.3). This data reduction procedure was applied to the FeSi medium rheology measurement. It demonstrates that FeSi medium exhibits a pseudoplastic trend with a yield stress. The apparent viscosities were calculated at two shear rates, 10 s⁻¹ that is assumed to be a typical shear rate in dense medium bath separators and 75 s⁻¹ for dense medium cyclones. A characteristic curve between apparent viscosity and medium density was established, which can be used in FeSi selection for dense medium separation. Medium stability was determined from the FeSi sedimentation rate measurement. It shows that medium stability was closely correlated with medium viscosity. A trade-off between stability and viscosity for optimal dense medium separation should be established.     

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.     

排采降压诱发煤层剪切破坏机理与防控对策

煤层压力衰减会导致煤岩体剪切破坏,诱发井壁失稳、套管损坏和出煤粉等井下复杂事故。为预防煤层破坏,以沁水盆地南部二叠系山西组3号煤层为研究对象,基于单轴应变模型分析了排采降压过程中的煤层应力路径及其破坏行为,明确了煤层破坏影响因素,并提出了控制井底流压和CO_2-ECBM相结合的防控技术对策。结果表明:煤层水平有效应力在排水阶段随孔隙压力的降低而线性增大,但在解吸阶段却随孔隙压力的降低而非线性减小,气体解吸能够加速煤层剪切破坏;煤层初始水平应力越小,垂向应力、初始孔隙压力、临界解吸压力越大,气体吸附效应越强,煤岩体弹性模量、泊松比越大,单轴抗压强度越低,则煤层临界破坏孔隙压力就越大;煤层破坏前转注CO_2既能有效避免煤层破坏,也可提高煤层气采收率,不失为CO_2-ECBM的良好作业时机。     

爆破振动作用下台阶边坡的动力响应及稳定性分析

运用FLAC^3D软件建立了某含夹层的双台阶顺层边坡数值模型, 分析了爆破振动作用下边坡动力响应规律, 并根据爆破后的塑性区分布图、剪应变增量图、水平方向位移云图对边坡的破裂面进行了分析, 研究了关键点位移、最大拉应力、抗剪屈服函数对边坡稳定性的影响, 结果表明, 随着爆心距增大, 振动幅值衰减规律为近大远小, 坡面以及坡内局部存在高程放大效应; 夹层影响着边坡动力响应规律, 爆心距相近时, 夹层之下的振幅大于其上的振幅; 夹层影响着边坡的变形和破坏方式, 分析岩体内部各点的最大拉应力和抗剪屈服函数可知, 对每级台阶而言, 坡脚是最容易受拉和受剪破坏部位, 坡顶后缘容易受拉破坏; 边坡动力稳定性可以通过对剪出口附近监测点的水平位移时程曲线进行判断, 发散则失稳, 收敛则稳定。研究结果对矿山边坡的减震与防护有一定指导意义。     

狮子山铜矿深部开采三维地应力实测及应力场分布研究

狮子山铜矿已进入深部开采阶段,针对深部巷道破坏严重、岩层移动加剧的现象,采用空心包体应力解除法对该矿进行三维地应力测量,共获取四个不同中段测点的三维地应力测试数据。地应力实测结果表明,四个中段测点的最大、最小主应力基本呈线性变化,最大主应力为45.59 MPa,随深度增加而增加,倾角变化范围为-8.68°～6.15°。最大水平主应力与垂直主应力的比值变化范围为1.41～2.75,说明矿区地应力以水平构造应力为主,剪应力值相对较大。九中段、十一中段、十二中段的最大主应力方向与矿体走向基本一致,而十五中段最大水平主应力方向与矿体走向近似垂直,地应力场的分布特征与工程地质调查和巷道变形调查结果相吻合。     

Recovery vs. mass pull: The link to air recovery

In recent years, developments in control strategy for banks of flotation cells have included process control based on mass pull. Mass pull, or the flowrate of solids reporting to the concentrate, is affected by changes in froth structure and stability which are in turn affected by changes in operating parameters such as air flowrate and froth depth.Air recovery, or the fraction of air entering a cell that overflows the lip as unburst bubbles, is a robust, non-intrusive measure of froth stability that passes through a peak as cell air rate is increased. Furthermore, it has been shown that when operating a cell at the air rate that yields the ‘Peak Air Recovery’ (PAR), an improvement in flotation performance, particularly mineral recovery, can be obtained.In this paper, results from industrial experiments are reported that compare the effect of air rate on air recovery and flotation performance, and specifically the effect on mass pull and mineral recovery. The results show that an increase in mass pull does not necessarily yield an increased mineral recovery in all cases, since it is dependent on whether the air rate must be increased or decreased to obtain the ‘Peak Air Recovery’. This work shows the potential gain to be made from control using air recovery measurements and operating at PAR conditions.     

考虑温度影响的充填料浆水平管流特性研究

为探究不同温度下充填料浆水平管流特性,开展了流变实验以获取不同温度下充填料浆流变参数,基于流体力学理论提出了充填料浆管道输送基本假设,利用COMSOL软件建立水平管道模型,分析了温度对料浆流态、流速、管道压力及管输阻力的影响.结果表明,温度升高,充填料浆塑性黏度和屈服应力降低;料浆在管道输送过程中壁面附近呈剪切流动,中...     

剪切载荷作用下岩体结构面动态接触特征数值模拟

准确认识岩体结构面的动态接触特征是评价和预测结构面剪切行为的基础.首先,通过FISH语言修正了FLAC3D软件自带的INTERFACE本构模型,使其能够准确表达粗糙结构面在剪切过程中的力学行为;然后,采用数值模拟和室内试验相结合的方法对剪切过程中结构面接触和受力的分布及其演化规律进行了研究,分析了法向应力和结构面粗糙度...     

全尾砂固结排放料浆流变特性实验研究

采用全尾砂固结剂TC-Ⅰ,通过全面试验、数据拟合、多元回归分析和理论计算等方法,对李楼铁矿未分级全尾砂固结排放料浆的流变特性及其影响因素进行了研究。结果表明,砂浆的剪切应力随着剪切速率增加而增大,呈线性相关;表观黏度随着剪切速率增加而减小,呈乘幂相关;测试范围内全尾砂固结排放料浆近似于宾汉塑性体模型,在管路输送中呈层流流态;浓度对全尾砂料浆的流变特性影响显著,灰砂比次之;同一灰砂比条件下,砂浆的屈服应力和黏度均随着浓度增加而增大;同一浓度条件下,灰砂比对砂浆的屈服应力和黏度影响不大;确定了适宜的砂浆浓度范围为76%~78%;建立了砂浆屈服应力、黏度关于浓度和灰砂比的回归模型。     

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.