浮选过程中的泡沫夹带研究进展

细粒矿物浮选过程中,亲水的脉石矿物泡沫夹带进入精矿中,导致精矿品位降低。揭示泡沫排液及排脉石过程中的相关理论,可以为浮选泡沫结构及泡沫夹带行为的研究提供理论基础。浮选过程中的脉石泡沫夹带是一种普遍现象,脉石夹带回收率与精矿水回收率呈线性关系;两相泡沫排液受重力、毛细作用力(表面张力)、黏滞力控制,不同含液率的两相泡沫排液遵循不同的排液公式;三相泡沫的排脉石过程遵循对流—扩散模型,脉石的夹带回收率受三相泡沫排液速率及脉石颗粒浓度分布控制。浮选操作条件、亲水脉石的特性、矿浆特性以及泡沫结构是影响泡沫夹带的主要因素;优化浮选操作条件,改变浮选流程结构和改变药剂制度可以有效降低脉石的泡沫夹带,提高浮选选择性。未来,还需开发表征浮选三相泡沫特征的方法、装置或仪器,三相泡沫的结构及形态、疏水矿物颗粒与亲水脉石颗粒在泡沫中的运动路径及分布规律、浮选三相泡沫排液及排脉石的数学模型还需要进一步的细致研究。另外,降低脉石泡沫夹带的技术对于部分浮选体系虽有一定效果,但脉石的泡沫夹带尚难以消除,须开发一些革命性的技术。     

浮选泡沫相中现象及机理研究进展

泡沫相(层)是浮选重要组成部分之一,决定了最终精矿品位和整体浮选效率。由于泡沫相中的气泡与颗粒的相互作用比较复杂,近些年国内外学者围绕浮选泡沫层开展了大量相关研究。本综述在介绍浮选泡沫的结构和性质后归纳了浮选泡沫失稳的机理,即排液、粗化和兼并在现阶段的研究进展。对颗粒强化泡沫稳定性的相关机理进行了分析和总结,且归纳出颗粒疏水性、粒度和形状是颗粒影响泡沫层稳定的主要因素。之后回顾了泡沫层中常见的泡沫夹带现象,分析总结了泡沫夹带的三个主要机理；颗粒物理性质、水回收率、湍流强度、矿浆浓度、泡沫层性质和表观气速是影响泡沫夹带的主要因素；夹带模型的建立对脉石夹带程度的有效预测以及浮选工艺流程的优化具有重要意义。最后提出在今后的研究中加强泡沫相流体力学研究和推进泡沫层颗粒追踪技术是浮选泡沫相研究的方向之一。     

无机盐对气液两相泡沫特性的影响研究

为更好地揭示并合理利用浮选过程中无机盐对浮选泡沫特性的影响,采用自制的泡沫特性测试系统,通过对两相泡沫不同高度处泡沫的静压强、气泡直径、泡沫柱的溢流流量进行测定,深入研究了无机盐对泡沫特性参数的影响规律.结果表明:在两相体系中,NaCl、Na2SO4、MgSO4及AlCl3这四种无机盐可显著减小各泡沫层高度下的气泡直径,增大泡沫含液率以及泡沫柱表观溢流速度,从而增大微细粒亲水脉石的泡沫夹带,而NaClO3的添加对泡沫特性参数均无显著影响.     

超声乳化煤油乳滴尺寸对泡沫性质及隐晶质石墨浮选的影响

本文提出采用乳化煤油的方法强化泡沫排液,改变泡沫性质,从而降低在隐晶质石墨浮选中脉石颗粒夹带的思路。将乳化剂、煤油和氯化钠溶液以2.5%、2.5%和95%的比例通过不同的复配方法混合,采用超声波处理制备出不同乳滴尺寸的乳化煤油,并探究了不同方法获得的乳化煤油对泡沫性质(如气泡尺寸、泡沫层高度和水回收率)和隐晶质石墨浮选过程中脉石矿物夹带的影响。研究结果表明:随着乳化煤油乳滴尺寸的减小,泡沫层高度和水回收率降低,隐晶质石墨浮选过程中脉石矿物的夹带量减少,浮选精矿品位和回收率均提高。     

煤泥浮选固体和水的回收特性研究

以河南某选煤厂细粒煤泥为研究对象,探究了中间密度级含量少的易浮煤泥在浮选过程中固体回收率、水回收量和高灰夹带量的变化规律,以及不同捕收剂与起泡剂用量对三者的影响,提出通过浮选精矿质量浓度反映浮选精煤灰分,为煤泥浮选效果预测提供新思路。试验结果表明,浮选过程中,单位时间固体回收率与水回收量基本符合一级浮选速度公式;随着浮选的进行,高灰细泥机械夹带进入精煤的比重减小,水流夹带逐渐占据主导作用;高捕收剂用量在较短时间内能达到较高精煤固体回收率,高起泡剂用量会显著增加精矿水回收量,同时也提高了高灰脉石的夹带量;相同浮选时间不同药剂量下精矿质量浓度与灰分呈较好的线性关系,对实际生产有一定的指导意义。     

脉石矿物在细粒煤浮选过程的夹带回收特性研究

以脉石矿物高岭石为研究对象,通过浮选速度实验研究了其在单独及掺配浮选条件下的回收特性,探究了起泡剂用量、浮选浓度、搅拌转速对浮选过程中高岭石回收率Rs、水回收率Rw、夹带率eg的影响.实验结果表明:单独浮选时,高岭石夹带率eg在浮选过程中基本不变,表现出"随水分配"的特征;掺配浮选时疏水性煤粒促进了高岭石回收,高岭石回收速率vs和夹带率eg随时间呈不断下降趋势;浮选过程中不断增加的起泡剂用量更加有利于降低脉石矿物的夹带回收,多点分段加药可能是有效的调控手段;低浓度浮选有助于减少高岭石的夹带回收,且该影响表现为浮选全过程;低搅拌转速可降低浮选前期高岭石夹带率eg,以减少脉石矿物回收率.     

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。     

优选药剂制度优化精矿品位和回收率

在选择和优化浮选药剂制度后,就有可能从布什维尔德杂岩的UG-2矿带中回收铂族金属和金(PGM Au).UG-2矿石的特点是有两种主要的脉石相(即铬铁矿和硅酸盐矿物),它们具有明显不同的物理和化学性质.设计了一种策略,以便在提高精矿品位前提下,可降低脉石的回收率而不会明显影响有价组分的回收率.由于PGM Au作为具有不同化学和物理性质的多种不同矿物产出这一事实,使有价组分的回收变得复杂,因此操作上就必须考虑到有价矿物的特征和最大限度回收,并满足严格精矿质量要求.进行了实验室试验,以查清各种浮选参数的影响.讨论了发生于浮选槽中的各种机理.本文证明了回收有价组分和脉石时夹带的重要性,更好地了解了这种非选择的子过程在整个回路控制中的作用.     

煤泥盐水浮选技术

盐水对浮选体系下颗粒与气泡行为的影响规律进行了综述。浮选矿浆中的无机盐电解质在提高精煤可燃体回收率的同时也增加了脉石矿物的回收。反电荷阳离子在煤粒表面吸附改善颗粒疏水性,颗粒-气泡间的液膜排液速度因双电层被压缩而加快;同时电解质兼有起泡剂的效果,能有效阻止气泡兼并聚合。另一方面,盐水浮选体系下细粒脉石颗粒的水流夹带和聚合截留现象严重,可燃体回收与脉石颗粒非选择性上浮之间的矛盾激增。     

高岭石在煤泥浮选中的夹带研究

为研究煤泥浮选过程中脉石矿物的夹带规律,进行了粗粒及细粒煤泥与高岭石掺配的浮选速度试验,并研究了粗粒及细粒级煤泥浮选中起泡剂用量、入料灰分、入浮质量浓度对高岭石夹带率及精煤灰分的影响。试验结果表明:煤泥浮选过程中,浮选精煤灰分表现出先减小后增大趋势,粗粒浮选精矿质量浓度高,脉石矿物的夹带程度不及细粒严重;起泡剂用量与入料灰分对粗粒及细粒夹带率影响较小,浮选质量浓度对其影响较大。浮选质量浓度由80 g/L降至40 g/L时,细粒夹带率由0.49降至0.25,精煤灰分由5.25%降至3.26%;粗粒夹带率由0.49降至0.41,精煤灰分由3.76%降至3.27%。     

Flotation frother mixtures: Decoupling the sub-processes of froth stability,froth recovery and entrainment

The flotation process consists of two distinct phases: the pulp and froth phase. One of the main roles of the froth phase is to create a suitable environment for the separation of floatable, valuable minerals from non-selectively recovered, entrained gangue minerals. As a result the froth phase plays a significant role in the metallurgical performance of industrial flotation cells. Froth stability is important for the recovery of valuable minerals. However, a stable froth may contribute to increased entrainment and, consequently, a lower grade.This study compares the effect of frother mixtures with that of their single component frothers on the froth stability, froth recovery and entrainment of a platinum-bearing UG2 ore using polyglycol and alcohol frothers. The study showed that frother mixtures resulted in a greater froth stability than either of their component frothers. The increased froth stability was reflected in increased froth recoveries and greater overall recoveries. However, the important aspect in the use of frother blends was that they altered the froth structure and resulted in a lower degree of entrainment. This, together with the increased recovery, resulted in higher grades of valuable mineral recovered to the concentrate when using the frother mixtures.     

Numerical and experimental study of the effect of a froth baffle on flotation cell performance

In this work, the effect of a froth baffle on flotation performance is investigated both experimentally and numerically. Flotation experiments with an artificial ore comprised of 80% silica as gangue and 20% limestone as floatable component were carried out to compare the flotation performance of a baffled froth system against an un-baffled froth system. The effect of the baffle’s inclination angle to the horizontal was also studied. Results indicated that a froth baffle has a profound effect on both recovery and grade. The presence of a froth baffle resulted in an increase in grade at the expense of recovery. The decrease in limestone recovery with the introduction of a froth baffle was found to be a function of the baffle’s inclination angle i.e. recovery decreased as the inclination angle becomes more acute. Water recovery as well as entrainment recovery herein represented by silica recovery decreased with decrease in baffle’s inclination angle. Numerical techniques were employed to model the experimental results. The 2D stream function equation/Laplace equation which is known to be adequate in describing froth transport was solved subject to boundary conditions that represent the presence of baffles. A solution was developed using finite difference methods on a rectangular map obtained using Schwarz–Christoffel (SC) mapping. Results from the simulations indicated a change in particle residence time distribution in a manner that reduces spread. The changes in residence time distribution helped in developing an explanation of the experimental data.     

Investigating froth stability: A comparative study of ionic strength and frother dosage

Valuable mineral recoveries and grades are strongly dependent on the stability of the froth phase within the flotation system; a stable froth zone allows for the efficient transportation of material for downstream processing, while entrainment of gangue is directly proportional to the amount of water recovered from the froth phase (Engelbrecht and Woodburn, 1975, Zheng et al., 2006a, Zheng et al., 2006b, Neethling and Cilliers, 2002). In an attempt to reduce the naturally floatable gangue (NFG) present in platinum bearing ores and to improve the grades of the valuable minerals, the use of high depressant dosages have been investigated. These high depressant dosages have significantly destabilised the froth phase in a number of studies (Bradshaw et al., 2005, Martinovic et al., 2005, Wiese, 2009). Wiese et al. (2010) has shown that an increase in frother dosage impacted the stability of the froth resulting in enhanced recovery of valuable minerals. In a separate study by Corin et al. (2011), the effect of an increase in the ionic strength of plant water on the stability of the froth was considered. As water restrictions become more stringent, many operations are recycling and reusing their process water causing an increase in the amount of dissolved ions present in the water, the effects of which are little understood. The same study also considered depressant addition at high dosages. It was noted that an increase in the ionic strength of the plant water increased the froth stability. This paper therefore compares the outcomes of increased frother dosage with increased ionic strength, and attempts to better understand the factors which influence the froth stability. The data presented in this paper forms part of much larger studies and complementary data has been published elsewhere (Wiese and Harris, 2012, Manono et al., 2012, Manono et al., 2013).     

The effect of the reagent suite on froth stability in laboratory scale batch flotation tests

In batch flotation tests conducted on ores from the Merensky reef, changes in froth stability invariably occur with variations in the reagent suite. The main reagents are collectors (primary and secondary), activators, depressants and frothers. Since the particles entering and leaving the froth in a batch flotation system are continuously changing, the stability of the froth can vary. Under these conditions the simplest measure of froth stability is the measure of water recovery at a fixed froth height. The batch flotation system developed at UCT allows for the separation of gangue which is entrained relative to gangue which is floated. It has been found that the presence of naturally floatable gangue (NFG) leads to froth stabilisation, whereas the presence of hydrophobic sulfide minerals may lead to destabilisation of the froth depending on the hydrophobicity (contact angle) of the sulfide minerals. This can vary with ore type since particle shape and amount of particles present can influence the extent of destabilisation. At low depressant dosages sodium isobutyl xanthate (SIBX) always results in lower froth stability than sodium ethyl xanthate (SEX). The frothing nature of dithiophosphate leads to increased froth stability and the addition of copper sulfate results in destabilised froths. Increasing depressant dosage reduces the stabilising influence of NFG and the depressant type (guar gum or CMC) also affects froth stability. Frother can be used in an attempt to overcome the destabilising effects of high depressant dosage. This work examines the effect of variations in the reagent suite and uses water recovered at a fixed froth height as an indication of froth stability in order to analyse these effects on the recovery of sulfide minerals, floatable gangue and entrained gangue.     

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.     

Modelling flotation with a flexible approach – Integrating different models to the compartment model

In this work, a comprehensive model structure for froth flotation is developed by linking the compartment model (Savassi, 2005) to a set of phenomenological models describing the froth recovery, the water recovery and the entrainment factor. This model structure is successfully calibrated against experimental data from a pilot plant campaign with a copper ore.     

Application of hydrophobic and magnetic plastic particles for enhanced flotation recovery

The effect of hydrophobic and magnetic plastic particles having a contact angle of around 83° on flotation performance was evaluated using coal particles of varying degrees of floatability. The magnetic plastic material were recovered by a low intensity magnetic separator and recycled back to the flotation feed for re-use. Flotation rate tests conducted on coal using a conventional cell proved that combustible recovery and flotation rate were significantly enhanced with the addition of the plastic particles, especially for difficult-to-float coals, which was corroborated by flotation column tests. Carrying capacity and particle size-by-size flotation tests further showed that the magnetic plastic particles preferentially increased the recovery of coarse particles by as much as 35 absolute percentage points due to froth stabilization which reduced the selective detachment of coarse and/or weakly hydrophobic particles. The enhanced flotation recovery was attributed to the influence on liquid drainage rate in the froth zone, froth stability, bubble coalescence and flotation rates.     

Effect of entrainment in bubble load measurement on froth recovery estimation at industrial scale

Froth recovery was calculated in a 130 m³ mechanical cell of a rougher flotation circuit. This was done by bubble load determinations along with mass balance surveys. Valuable grade in the bubble load decreased in the −38 μm due to fine particles entrained to the chamber of the device. The effect of fine particle entrainment on froth recovery was evaluated. A comparison between results from the raw bubble load data (assuming all particles were transported by true flotation) with those from corrected bubble load information (subtracting fine particle entrainment) was carried out. Entrainment occurred due to hydraulic transport in the bubble rear, which corresponds to the worst case scenario for froth recovery estimation. Results showed that the relative error was less than 0.3%, which allowed validation of the bubble load measurement as an effective methodology for froth recovery estimation at industrial scale.