Computer simulation of fluid motion in a porous bed using a volume of fluid method: Application in heap leaching

Heap leaching is a process extensively used by the mining industry to recover metals from low-grade ores and large quantities of submarginal material resources. Understanding flow through a packed particle bed is important to enhance the performance of heap leaching with respect to design and operating considerations. Complex fluid behavior in porous media, such as film flow, fragmentation, coalescence of droplets, and rivulet flow with or without meandering, has been widely observed in laboratory experiments. In this study, to provide detailed information of momentum and mass transfer phenomena in a granular bed direct numerical simulations (DNS) were performed. In this case the liquid–gas flow through a granular bed was considered comprised of monosized, spherical, solid particles arranged randomly in a cylindrical container. The volume of fluid (VOF) method was used to compute velocity field as well as liquid volume fraction distributions in the container. The results obtained suggest that the liquid phase distribution in the bed is mainly controlled by surface tension and particle induced turbulence appears to have insignificant effects. These results allow us to obtain a better understanding of the fundamental physics governing unsaturated fluid flow. This finding seems to have a significant impact in the design of efficient multi-phase reactors for heap leaching and bioleaching processes.     

堆浸工艺中溶浸剂的作用机理与流动特性

分析了溶浸剂的作用机理,认为堆浸浸出过程是一个多相反应动力学过程,浸出速度与溶解化学反应速度、反应物和生成物的扩散速度等因素有关。根据多相反应扩散动力学理论,给出了化学溶浸剂溶浸开采金属的定量描述。在假定裂隙岩体为拟连续介质,流体在整个岩体中的流动规律服从Darcy定律的条件下,导出了溶浸剂在多孔介质中流动的孔-裂隙二重非稳定渗流数学模型。     

多孔介质中的流动、传热与化学反应

矿业工程中的许多生产实际问题都可以归结为多孔介质中的传递问题。多孔介质分布广泛,研究其中的流动、传热与化学反应问题具有重要的实际应用和科研价值。评述了多孔介质中流动、传热与化学反应的研究现状,分析了3个过程之间的相互关系。指出流动作为一种输运方式,携带物质和热量沿流动方向进行迁移,引起物质浓度和温度分布的改变,对传热和化学反应过程产生影响;传热通过改变温度分布,引起流体物理性质和化学性质的改变,进而影响流动和化学反应;化学反应通过消耗反应物和生成产物,改变多孔介质的孔隙结构,改变孔隙流体的物理化学性质,改变固体和流体的传热性质,进而影响流动和传热。分析表明,化学反应作为发生在微观尺度上的过程,对宏观的流动和传热过程具有明显的影响,要对这种影响进行定量描述必须发展新的跨尺度的分析、测试和计算方法。     

氨浸络合罐体出入口结构对络合浓度的影响研究

利用多孔介质多场耦合、化学反应传质等相关理论,采用Comsol Multiphysics仿真软件进行数值模拟,研究了氨浸过程中氨水在氧化铜矿石颗粒之间的流速、压强和生成物浓度,文章探讨的模型分别从罐体中部的左、中、右三个部位设置入口,罐体下部的右侧和中测设置出口,考察了氨浸罐不同出口和入口位置对氨浸过程中铜氨络合物浓度的影响,获得了相应的铜氨络合物浓度及氨浸罐中液体的流速和压力分布等动力学过程。结果表明:改变氨浸罐出口和入口的位置可以明显影响铜氨络合物的生成浓度,氨从氨浸罐中部进入并从氨浸罐底部右下角流出速度大、氨浸效果好,氧化铜颗粒与氨反应充分,所获得的铜氨络合物浓度最高。研究成果对氨浸络合工艺装备设计具有重要指导意义。      

压力波动法地浸采铀的数值模拟初步研究

目前国内外的地浸研究侧重地浸化学机制及工艺,不能很好地解决铀矿层非均质性引起溶浸流体非均质流动带来的非优势流动区域和溶浸死区等问题。基于流动传质理论、室内试验和注气现场试验,笔者提出了压力波动溶浸开采的方法,即采用高压缩性的气液混合溶浸流体进行压力波动条件下的地浸开采。基于分散相气液混合流体特性和流动-反应-传质理论,采用COMSOL-Multiphysics软件模拟了传统中性地浸和压力波动法地浸的采铀过程。数值模拟结果显示:压力波动过程中,溶浸流体在矿层中胀缩变形,可促进高渗透区域与低渗透区域的流体流动传质过程,特别是低渗区域的对流-弥散传质作用;铀回收率随压力波动次数变化而变化,回收率曲线明显区别于传统地浸回收率曲线,铀回收速率和回收率提高。初步结果表明,压力波动法地浸对提高非均质铀矿层的回收速率和回收率在技术上具有可行性。     

淋滤浸出过程的流体力学和传质

本文总结了淋滤过程的流体力学行为的初步研究结果。根据矿石堆粒层中溶液的存在形态及多孔介质扩散过程的基本概念提出的淋滤过程传质模型—孔隙扩散控制的“双膜传递过程”，已被试验结果所证实。     

Liquid axial dispersion and holdup in column leaching

The liquid phase hydrodynamics in column and heap leaching is a key design aspect that has attracted some attention, but was not yet completely elucidated. On the other hand, conventional trickle bed catalytic reactors have received enormous attention for many decades; however, the operational variables range in this case is generally far from the column and heap leaching processes. This paper presents a hydrodynamic study performed in a bench scale column, where the axial dispersion and the liquid holdup, as a function of the liquid flow rate, are estimated using residence time distribution experiments. The normalized tracer concentrations are fitted using a non-linear least square method and the piston-dispersion-exchange model that is solved numerically using the finite differences method. The trends of axial dispersion, dynamic and static saturation, and exchange coefficient for mass exchange between mobile and stagnant phases, showed excellent agreement with previous results for low Reynolds number in conventional trickle bed reactors. In this study, these experimental results and empirical correlations are presented. The dynamic saturation of the bed increases with the flow rate while the static saturation decreases slightly. The axial dispersion is weak dependent of the liquid flow rate, but is non-negligible and should be accounted for in the mathematical modeling of heap and column leaching process.     

Determination of oxygen solubility in aqueous sulphuric acid media

Oxygen is an essential element in numerous hydrometallurgical leaching processes where it acts as a primary or a secondary oxidant in the dissolution of sulphic concentrates. A common acidic leaching medium is sulphuric acid. It was found crucial to define experimentally the solubility and the rate of mass transfer of oxygen in various sulphuric acid environments prior to direct leaching experiments of sulphuric zinc concentrates, and a laboratory scale equipment was developed for the analysis of oxygen concentrations in aqueous acid media. This paper discusses the solubility and dissolution of oxygen as a function of temperature and concentration of sulphuric acid. Also, the effect of temperature (25–55 °C), gas flow rate (0.75–2.25 l/min) and acid concentration (up to 2 M) on the mass transfer coefficient k_La between gas and liquid is evaluated.     

Use of mesh adaptivity in simulation of flow in packed beds – A case study

Computational modelling of transport phenomena in packed beds is of interest in a wide range of engineering applications. We simulate flow in packed beds with similar conditions to heap leaching processes. The governing equations are the conservation of mass and Darcy’s law. The primary variables are pressure and saturation. To discretize the governing equation, a control volume finite element method is used. The numerical scheme is implemented in Fluidity, a general purpose flow simulator that is equipped with anisotropic mesh adaptivity techniques to control local solution errors and increase computational accuracy. We demonstrate the application of the developed method to solve for incompressible flow of air and liquid within packed beds of mono-dispersed non-porous particles and compare our results with experimental measurements by Ilankoon and Neethling (2012). To study the effect of heterogeneity on flow regime in packed beds, an experiment is conducted on a packed bed consisting of two regions with different particle sizes. The non-uniform packed bed is also simulated numerically and our comparison shows very good agreement. Mesh adaptivity resolves saturation fronts in two regions of the column with high-resolution meshes and reduces the discretization error. This study serves as a validation for our numerical approach for prediction of hydrodynamics of heap leaching processes at large scales.     

堆浸工艺中溶质运移的数学模型及其解析解

堆浸工艺中溶质的运移可归结为多孔多相介质中的传质运动。溶质在矿堆中的输运与分布将受到对流、分子弥散、机械逸散、不动水效应、化学反应等多种物理和化学因素的影响, 使溶质的运移变得十分复杂, 并难以定量描述。综合考虑以上影响因素, 分别建立了堆浸中可动和不可动区溶质运移模型。根据质量守恒定律, 推导出堆浸过程溶质运移的基本方程, 在忽略对流的情况下, 给出了方程解的解析表达式, 并由此确定水动力弥散系数。针对某工程实例进行计算, 计算结果较为合理。     

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.     

铀矿石堆浸技术应用与效益分析

本文论述铀矿石堆浸、降低成本、提高效益的问题。讨论了搞好堆浸的决策原则和主要工作,介绍了堆浸技术经济分析、工艺流程选择和治理“三废”的有关方法及要求。认为铀矿床的天然特征和做好铀矿堆浸试验是开展铀矿堆浸的前提;而因地制宜、建好矿堆、确定合适的喷淋、浇灌方式是提高堆浸浸出率的技术关键。文章还就发展堆浸、建立试验和工业生产考核指标、提高堆浸技术水平、采取有效的环保措施,提出了看法和建议。     

原地溶浸开采中的多过程耦合作用与反应前锋运动:2.数值模拟

基于流体流动、溶解反应、孔隙度变化、质量守恒等机理建立了原地溶浸开采的多过程耦合与反馈的动力学模型,并编制了模拟程序。应用该模型和程序可以对原地溶浸开采过程中反应前锋的运动进行数值模拟。以用硫酸和氧化剂配制的溶液作溶浸剂的原地溶浸采铀为例,数值模拟结果表明,无论是在均匀孔隙岩石中还是在非均匀孔隙岩石中都可产生复杂形态的反应前锋运动,反应前锋的运动特征和形态稳定性与流体流速和模拟区域大小有关。反应前锋的动力学模拟与研究在原地溶浸采铀的生产和技术研究中有重要意义和应用前景。     

原地浸出采矿中溶浸剂的作用机理与流动特性

分析了溶浸剂的作有机理,认为原地浸出过程是一个多相反应动力学过程,浸出速度与溶解化学反应速度、反应物和生成物的扩散速度等因素有关。根据多相反应扩散动力学理论,建立了地浸中化学溶浸剂溶浸开采金属的数学模型。在假定裂隙岩体为拟连续介质,流体在整个岩体中的流动规律服从Darcy定律的条件下,导出溶浸剂在裂隙介质中的流动物性方程和渗流数学模型。     

堆浸过程中堆场地质灾害发生机制探讨

堆浸过程中,存在着滑坡和泥石流两种地质灾害。分析了灾害产生的原因及其可能造成的危害,探讨了堆浸场地质灾害发生机制的宏观表象与微观反应之间的内在联系;重点分析了微观机理中溶浸液在堆场中的赋存状态以及矿石颗粒内部的反应过程。以铜浸出为例,分析了铜浸出过程中的化学反应机理。     

煤粉颗粒团燃烧过程的数值模拟

煤粉的燃烧在工程实际中很多情况下都是聚团燃烧,颗粒内部传热传质机理复杂。本文根据多孔介质的传热传质学理论,引入对流项,建立了气流场中煤粉团燃烧的三维数学模型,并对不同孔隙率的煤粉团的燃烧过程进行了对比计算,计算结果合理,揭示了孔隙率对煤粉团着火燃烧的影响,为深入研究煤粉团燃烧特性打下基础。     

离子型稀土矿浸出渗流规律与调控方法研究

离子型稀土矿床成因与矿石性质复杂,矿体特有的黏土矿物不仅不利于稀土离子的渗流浸出,而且易产生药剂残留、渗流盲区,还可能引发山体滑坡等地质环境灾害。为给离子型稀土矿原地溶浸、高效回收工艺以科学指导,从原地溶浸化学反应、渗透规律、浸出动力学、水动力学、铝动力学等角度深入分析了离子型稀土矿浸出渗流规律研究现状,指出了原地溶浸过程存在的问题和发展方向,总结探讨了浸出渗流过程的调控方法。结果表明,以理论为指导,开发高效、经济、环保型浸出剂,研发助浸、抑杂、防膨、促渗等辅助药剂,改善注液、收液方式将是离子型稀土矿原地溶浸工艺优化的主要方向。     

某铁帽型金矿堆浸技术方案比较

介绍了某铁帽型金矿氧化矿石堆浸方案比较结果。对现场实际堆浸工艺、细粒堆浸工艺及细粒预浸—助浸工艺进行了初步技术经济分析，认为后者经济效益最佳     

预先分级联合选别提高某低品位铜矿金属回收率试验

某大型低品位金铜矿山较高品位铜矿石选用浮选工艺进行富集,低品位铜矿石则利用生物堆浸工艺生产阴极铜,该矿山生物堆场随着堆高的增加,酸铁不断浸出、铜浸出率下降。针对该生物堆浸低品位铜矿石,采用预先分级、选冶联合工艺,并对原有堆浸工艺进行优化,2 mm筛上产品柱浸试验浸出率为75.22%,比原工艺流程浸出率提高了5.08个百分点,铁累积浸出率同比下降了2.75个百分点。-2 mm产品通过浮选工艺最终可获得含铜20.20%、回收率87.21%,伴生金品位3.6 g/t、金回收率58.74%,伴生银品位83.7 g/t、银回收率为68.28%的铜精矿,以及含硫47.12%,回收率33.00%的硫精矿。预先分级、选冶联合工艺铜综合回收率为79.55%,较原生物浸出工艺铜浸出率69.14%提高10.41个百分点,并伴生回收贵金属金、银及副产品硫精矿,使用该工艺可增加利润约1.16亿元。工艺改造后不仅可提高资源利用率,产生较大的经济效益,还可降低酸铁的浸出,大大降低环保处理成本。