Prediction of wear and its effect on the multiphase flow and separation performance of dense medium cyclone

Dense medium cyclone (DMC) is a high-tonnage device that is widely used to upgrade run-of-mine coal in modern coal preparation plants. It is known that wear is one of the problems in the operation of DMCs, but it is not well understood. In this work, the wear rate of DMC walls due to the impact of coal particles is predicted by a combined computational fluid dynamics and discrete element method (CFD-DEM) approach, using the Finnie wear model from the literature. In the CFD-DEM model, DEM is used to model the motion of discrete coal particles by applying Newton’s laws of motion and CFD is used to model the motion of the slurry medium by numerically solving the local-averaged Navier–Stokes equations together with the volume of fluid (VOF) and mixture multiphase flow models. According to the Finnie wear model, the wear rate is calculated according to the impact angle of particles on the wall, particle velocity during an impact and the yield stress of wall material; the relevant particle-scale information can be readily obtained from the CFD-DEM simulation. The numerical results show that the severe wear locations are generally the inside wall of the spigot and the outside wall of the vortex finder. The wear rate depends on both the operational conditions and solids properties. It increases generally with the decrease of medium-to-coal (M:C) ratio. For a given constant M:C ratio, the wear rate for thermal coal is higher than that for coking coal, especially at the spigot. Large particles may cause a non-symmetric wear rate due to the gravity effect. The effect of a worn spigot wall on the multiphase flow and separation performance is also studied. This work suggests that the proposed approach could be a useful tool to study the effect of wear in DMCs under different conditions.     

DEM validation of media shape effects on the load behaviour and power in a dry pilot mill

Simulations were carried out in Metso’s DEM simulator so as to draw up an understanding of the effects the various ways of defining media shapes within the simulator have on the load behaviour and mill power draw. Wits University made available the load behaviour and mill power draw experimental results for the spherical balls, worn balls and cylpebs so as to validate the DEM simulations. The spherical media were defined by a regular spherical shape model and a multi-faceted polyhedron model. Worn balls were defined by super quadric models. A comparison was made between spherical media shapes, non-spherical single media shapes and a distribution of non-spherical media shapes and sizes in representing a load comprised of worn balls. The effect of increasing angularity of non-spherical media shapes on mill power was investigated. The cylpebs were modelled using a regular cylindrical shape model and the effects of friction on the power drawn were determined.     

Studies on grinding media wear and its effect on flotation of ferrugenous phosphate ore

Marked ball grinding tests were carried out in the laboratory with a low grade phosphate ore under different experimental conditions. Two types of balls were used, namely high carbon low alloy (HCLA) cast steel and high chrome cast iron. Results of marked ball grinding tests indicated that ball wear increased with time and showed a sharp increase for wet grinding over dry grinding. Ball wear under wet grinding conditions was also influenced by the gaseous atmosphere in the mill. The grinding ball materials could be arranged in the following order with respect to their overall wear resistance:High chrome cast iron > HCLA cast steel ballsMethods to minimize ball wear through control of mill atmosphere and addition of flotation reagents are discussed. Effect of grinding media and additions of flotation reagents during grinding on phosphate ore flotation are also discussed.     

Wear performance and cost effectiveness––a criterion for the selection of grinding media for wet milling in mineral processing operations

Experiments to evaluate the milling performance, hence the relative cost effectiveness index of selected grinding media were conducted in a laboratory scale ball mill. The five types of grinding mill balls studied were eutectoid steel, low alloy steel, medium chromium cast iron, cast semi-steel and unalloyed white cast iron. The results obtained show that the heat-treated medium chromium cast iron ball possess a superior combination microstructure, wear resistance, and despite its high price per tonne, cost effectiveness.     

Prediction of slurry transport in SAG mills using SPH fluid flow in a dynamic DEM based porous media

DEM modelling of the motion of coarse fractions of the charge inside SAG mills has now been well established for more than a decade. In these models the effect of slurry has broadly been ignored due to its complexity. Smoothed particle hydrodynamics (SPH) provides a particle based method for modelling complex free surface fluid flows and is well suited to modelling fluid flow in mills. Previous modelling has demonstrated the powerful ability of SPH to capture dynamic fluid flow effects such as lifters crashing into slurry pools, fluid draining from lifters, flow through grates and pulp lifter discharge. However, all these examples were limited by the ability to model only the slurry in the mill without the charge.In this paper, we represent the charge as a dynamic porous media through which the SPH fluid is then able to flow. The porous media properties (specifically the spatial distribution of porosity and velocity) are predicted by time averaging the mill charge predicted using a large scale DEM model. This allows prediction of transient and steady state slurry distributions in the mill and allows its variation with operating parameters, slurry viscosity and slurry volume, to be explored.     

Analysis of stirred mill performance using DEM simulation: Part 2 – Coherent flow structures, liner stress and wear, mixing and transport

Stirred Mills are becoming increasingly used for fine and ultra-fine grinding. This technology is still poorly understood when used in the mineral processing context. This makes process optimisation of such devices problematic. 3D DEM simulations of the flow of grinding media in pilot scale tower mills and pin mills are carried out in order to investigate the relative performance of these stirred mills. In the first part of this paper, media flow patterns and energy absorption rates and distributions were analysed to provide a good understanding of the media flow and the collisional environment in these mills. In this second part we analyse steady state coherent flow structures, liner stress and wear by impact and abrasion. We also examine mixing and transport efficiency. Together these provide a comprehensive understanding of all the key processes operating in these mills and a clear understanding of the relative performance issues.     

地下选矿厂磨机(半自磨机)机械振动研究综述

地下选矿厂磨矿硐室(半自磨机硐室)需要承受磨矿设备筒体内矿石、介质和筒体交互冲击产生的机械振动作用。对国内外学者及工程技术人员针对与半自磨机类似的球磨机、磨煤机等设备,从数据采集及分析方法、改进设备作业效率、监控设备运行性能及保持设备基础稳定方面取得的研究成果进行了综述,总结了磨机(半自磨)机械振动信号采集、分析识别方法、仿真反演及实际应用等方面研究成果,具有较高的借鉴意义。     

离心泵叶轮内颗粒轨迹与磨损的关系

通过对离心泵叶轮内颗粒轨迹影响因素的分析,得到了颗粒轨迹与磨损的关系。     

岩质高陡边坡结构特征及变形特征分析

营盘山高陡边坡最大坡高110 m,沿坡面走向宽400m,是典型的缓倾内层状岩质高边坡。利用离散单元方法(DEM),模拟分析了该岩质边坡采石切坡前及采石切坡后的变形破坏及其演变过程。     

块裂介质岩体变形与气体渗流的耦合数学模型及其应用

在详细论述岩体基质岩块与裂缝变形,气体渗流及相互作用物理机制的基础上,提出了块裂介质岩体变形与气体渗流的耦合数学模型及其数值解法,这是岩体介质固气耦合数学模型的重要发展,以含裂缝煤层瓦斯抽放为例,通过数值分析,揭示了含裂缝煤层瓦斯在基质岩块和裂缝中运移,传递和交换,伴随的岩体裂缝和基质岩块变形和应力分布,及其对瓦斯气体运移的相互作用影响规律。     

低位综放开采顶煤放出的散体介质流理论与应用

由于放煤口布置方向的差异，放矿椭球体理论的适用条件与低位放煤综放开采的放煤过程有本质差异，因此基于模拟试验、FLAC计算、离散元模拟计算和现场观测，提出了散体介质流理论模型，揭示了低位综放开采中顶煤流动与放出的真实过程，并且成功地指导了现场放煤工艺与参数的确定。     

铝土矿选矿研究现状与孝义地区的建厂可行性

简介了铝土矿选矿技术的现状，阐述了在孝义地区建设铝土矿选矿厂的便利条件，认为在该地区建设铝土矿选厂是可行的，而且是必要的。     

基于流态转捩的非线性渗流模型及在陷落柱突水机理分析中的应用

岩溶陷落柱突水是威胁煤矿安全生产的重大灾害之一。基于陷落柱突水过程中流体流态转捩（含水层层流到巷道紊流）的渗流本质,建立了三流场（Darcy层流、Forchheimer流和N-S紊流）耦合非线性渗流模型,并应用于骆驼山煤矿“3·1”底板陷落柱突水数值模拟分析。结果表明：随着突水流体流速不断增大,陷落柱Forchheimer流由黏滞阻力为主,到黏滞阻力和惯性阻力共同作用,最后到惯性阻力为主发生了质的变化,陷落柱突水是流体渗流从渐变到突变的动态过程。进一步表明采用Forchheimer方程描述陷落柱内高速非线性层流,能够较好地反映水流从含水层达西层流到巷道紊流的中间状态,可以定量揭示陷落柱突水三种流态转捩的渗流本质。     

The colouring effect of pyrrhotite and pyrite on micronised calcium carbonate slurries for the paper industry

Brightness (R457) is the main quality parameter in the production of ground calcium carbonate (GCC) slurries for the paper industry. In order to study how the presence of trace amounts of pyrrhotite (Fe_(1−x)S) and pyrite (FeS₂) affect the brightness of GCC slurries, experiments were performed in which a high quality calcite concentrate was spiked with these sulphides prior to micronisation and subsequent spectrophotometric measurements. The results show that even very small additions (<0.05 wt%) have a significant detrimental effect on the brightness of the product. Pyrrhotite reduces the brightness of the product more than pyrite, probably as an effect of differences in inherent optical reflectivity, specific surface area after micronisation and smearing. In addition, the experiment shows that when brightness is presented as a function of iron concentration, magnetite (Fe₃O₄) produces a different result compared to the sulphides. This indicates that a simple iron analysis is not sufficient to predict brightness of the GCC slurry when several iron-bearing minerals are present. The particle size distribution of the contaminant phase has proven to have a significant effect, as brightness is reduced when the contamination becomes more finely distributed.     

河北某地鲕状赤铁矿工艺矿物学研究

在对某地矿石化学成分、矿物组成、矿石结构构造、矿石工艺粒度、矿物嵌布特征等工艺矿物学研究的基础上,对矿石不同磨矿细度条件下产品解离度及原矿筛析指标等进行了系统考查,为确定合理的选矿工艺流程及条件提供了依据。     

铁介质磨矿对锂辉石和绿柱石浮选影响的分子模拟计算研究

利用分子模拟计算方法,研究了铁球作为磨矿介质,十二胺和油酸钠分别作为捕收剂,锂辉石和绿柱石与捕收剂在磨矿前后的相互作用能。结果表明,这两种典型硅酸盐矿物经过铁球磨矿后,矿物表面吸附的铁,使阳离子捕收剂十二胺与矿物的相互作用能增大,阴离子捕收剂油酸钠与矿物的相互作用能减小,进而影响捕收剂与矿物之间的相互作用。总体来讲,锂辉石和绿柱石经过铁球磨矿后,一般会阻止十二胺阳离子捕收剂在矿物表面的吸附,而对于油酸根阴离子捕收剂,则起到一定的活化作用,有利于油酸根离子在矿物表面的吸附。     

The effect of acrylamide-co-vinylpyrrolidinone copolymer on the depression of talc in mixed nickel mineral flotation

Copolymers of acrylamide and vinylpyrrolidinone with varying compositions have been synthesised and employed to depress talc in a model flotation system with process plant operation conditions. Adsorption isotherms indicated that the hydrophilic acrylamide homopolymer has a very low affinity for the hydrophobic talc surface, whereas vinylpyrrolidinone homopolymer strongly adsorbs onto the talc surface. Micro-flotation experiments revealed that the copolymer system can induce stronger talc depression than the homopolymer variants, with the most effective copolymer depressant having 25-30% vinylpyrrolidinone incorporation. The copolymer system is observed to have inherited the strong talc affinity of vinylpyrrolidinone polymer and the strong hydrophilic property from polyacrylamide. This combined effect facilitates the desired strong talc depression in single mineral flotation. However, this copolymer system has similar adsorption affinity on both the talc and pentlandite, hence depressing both talc and pentlandite in the mixed mineral flotation system. This research shows that a sufficient hydrophobic balance on the polymer is necessary for the adsorption and subsequent depression for talc. However, polymer with high adsorption selectivity is required to be a successful synthetic talc depressant for mixed mineral system.     

齐选厂与东烧厂二次磨矿介质消耗研究

提出了按矿石性质、粒度要求、工艺设备不同进行磨矿介质消耗研究的新方法.在对齐大山和东鞍山铁矿石磨矿功指数及可磨度进行研究的基础上,计算分析了齐大山选矿厂与东鞍山烧结厂二次磨矿介质理论和实际的消耗及对比情况,指出相关磨矿作业应加强降低磨矿介质消耗的研究工作.