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.     

The interaction of clay minerals with gypsum and its effects on copper–gold flotation

The interaction of two clay minerals, kaolinite and bentonite with gypsum and its effects on the flotation of a copper–gold ore was investigated in this study. It was found that bentonite increased the viscosity more than kaolinite when mixed with the copper–gold ore at low shear rates. The detrimental effect of these clay minerals on flotation was attributed to the entrainment of clay particles when kaolinite was added to the ore and to a decrease in true flotation by bentonite. Bentonite formed a sponge-like structure with predominant edge–edge (E–E) interactions which might affect hydrodynamics in the flotation cell and have a detrimental effect on flotation recovery. Kaolinite did not form a particular network structure and its aggregates mostly consisted of face–face (F–F) type associations which did not affect flotation hydrodynamics. The addition of gypsum to the ore–bentonite mixture inhibited the formation of interconnected network structures. This led to lower viscosity values with flotation behaviour similar to that of mixtures with kaolinite. In this case, there was an improvement in recovery, but the grade decreased due to entrainment. The addition of gypsum to the ore–kaolinite mixture created aggregates with long strings further enhancing particle entrainment with more mass transported to the froth.     

起泡剂对硫化矿浮选的影响

研究了起泡剂MIBC、BK201、松醇油及2-乙基己醇对石英及黄铁矿单矿物浮选行为的影响, 并进行了实际矿石浮选试验。单矿物试验结果表明: 石英通过泡沫夹带进入浮选精矿, 而黄铁矿通过疏水上浮和泡沫夹带的双重作用进入浮选精矿。不同起泡剂作用下, 精矿中泡沫水回收率越高, 石英和黄铁矿的浮选回收率越高, 不同起泡剂对石英和黄铁矿具有不同的夹带效果, 使石英和黄铁矿浮选回收率最高的起泡剂分别为BK201和MIBC。实际矿石浮选试验表明: 浮选产率、精矿品位及回收率与泡沫水回收率密切相关, 泡沫水回收率增大, 精矿产率增大, 而品位降低。选择合适的起泡剂能够增加硫化矿物的回收率并降低石英的回收率, 获得较好的浮选分离效果。     

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.     

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.     

起泡剂对凝灰岩型氧化铜矿中微细矿泥可浮性的影响

通过凝灰岩型氧化铜矿中微细矿泥(-20μm)上浮率试验、润湿接触角和泡沫水回收率测定,考察矿泥天然可浮性、泡沫水回收率、起泡剂种类及用量对矿泥可浮性的影响。结果表明,矿泥天然疏水性低,起泡剂不能增加矿泥的疏水性,但起泡剂增加了泡沫水回收率,泡沫水夹带是导致矿泥上浮的主要原因。不同种类起泡剂对微细矿泥的上浮率有不同的影响,影响程度按二乙二醇丁醚,MIBC、松醇油依次降低。为减少凝灰岩型氧化铜矿浮选中矿泥的影响,选择合适的起泡剂和降低起泡剂用量是必要的。     

Rougher flotation of copper sulphide ore using biosolids and humic acids

In the quest of new, less hazardous, and more ambient-friendly froth flotation reagents, the use of biosolids or humic acids as both collector and frother for the concentration of copper sulphide ores was investigated. Rougher flotation tests were conducted in Denver cells on a laboratory scale, and metallurgical indicators such as copper recovery, copper concentrate grade, and concentration and enrichment ratios were compared with those obtained under similar conditions but using conventional collectors and frothers for the industrial flotation of copper sulphide ores. With a dosage of 10% (w/w) biosolids, copper recovery and grade were 26% and 0.81%, respectively. The copper recovery and grade obtained with 1.5% (w/w) salt of humic acids were 29.7% and 3.5%, respectively. A significantly higher copper recovery (65.1%) was obtained with conventional industrial collectors and frothers, but the grade was also low (3.1% Cu). With the same dosage of humic substances, humic acid show that the flotation rate constant was significantly higher (0.2 min⁻¹) than that obtained with the same dosage of biosolids (0.09 min⁻¹). These results indicate that humic acids have more affinity than biosolids for copper-containing mineral species, and also show that biosolids and humic acids could be used as both collector and frother in the sulphide mineral concentration process by froth flotation. Because the distribution of iron in the concentrate obtained with biosolids is highest, these materials seem to have more affinity for pyrite.     

煤泥浮选过程中的细泥夹带与罩盖机理

选用开滦矿区钱家营矿的高灰难选煤泥和大同塔山选煤厂煤系高岭石,通过单矿物和混合矿物浮选试验研究了影响高灰细泥夹带和罩盖的主要因素。研究发现：影响高灰细泥夹带的主要因素为细泥粒度、起泡剂用量和矿浆浓度,捕收剂用量对其影响较小;矿浆pH值接近8时,可燃体回收率最大。EDLVO理论计算发现：微细粒的高岭石与煤粒间存在着“能垒”,当颗粒间距约为30 nm时,“能垒”达到最大值;高岭石的粒度越细,“能垒”越低。外界能量输入可以打破“能垒”,使细泥颗粒发生罩盖。试验表明：强烈的机械搅拌使混合煤样的精煤产率和可燃体回收率分别降低10.87%和13.16%。     

Modelling of entrainment in industrial flotation cells: Water recovery and degree of entrainment

Entrainment in flotation can be considered as a two-step process, including the transfer of the suspended solids in the top of the pulp region just below the pulp–froth interface to the froth phase and the transfer of the entrained particles in the froth phase to the concentrate. Both steps have a strong classification characteristic. The degree of entrainment describes the classification effect of the drainage process in the froth phase. This paper briefly reviews two existing models of degree of entrainment. Experimental data were collected from an Outokumpu 3 m³ tank cell in the Xstrata Mt. Isa Mines copper concentrator. The data are fitted to the models and the effect of cell operating conditions including air rate and froth height on the degree of entrainment is examined on a size-by-size basis. It is found that there is a strong correlation between the entrainment and the water recovery, which is close to linear for the fines. The degree of entrainment decreases with increase in particle size. Within the normal range of cell operating conditions, few particles coarser than 50 μm are recovered by entrainment. In general, the degree of entrainment increases with increase in the air rate and decreases with increase in the froth height. Air rate and froth height strongly interact with each other and affect the entrainment process mainly via changes in the froth retention time, the froth structure and froth properties. As a result, other mechanisms such as entrapment may become important in recovering the coarse entrained particles.     

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.     

The effect of frother blends on the flotation performance of selected PGM bearing ores

Concentrators processing PGM bearing ores make use of polysaccharide depressants to reduce the recovery of the undesired naturally floatable gangue minerals, mainly silicates, present in the ore. Recent work has shown that high depressant dosages can completely depress naturally floatable gangue and thus prevent it from reporting to the concentrate. These high depressant dosages can, however, have a negative effect on the recovery of valuable minerals present in the ore by reducing the stability of the froth. In order to counterbalance the effects of depressant addition, frothers are added. It is, however, preferable to maintain independent control over bubble size and froth stability which is difficult to achieve with only one frother. An alternative strategy is to use a blend of frothers, e.g. a weaker frother in combination with a stronger frother. Such a system allows an additional degree of freedom: changing the ratio of the two frothers provides more independent control of bubble size and froth stability. This study demonstrates through the use of batch flotation tests how blending low molecular weight alcohols with commercially available frothers impacts the solids and water recovery, as well as the valuable mineral recovery and concentrate grade in different PGM ores. Higher water and solids recoveries together with higher valuable mineral recoveries (>90% copper and >70% nickel) were obtained from tests using frother blends.     

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。     

Effects of frother type and froth height on the flotation behaviour of chromite in UG2 ore

About 70% of the UG2 reef consists of the gangue mineral chromite (FeO · Cr₂O₃). In the processing of UG2 ore by flotation for the recovery of platinum group elements (PGEs) the presence of chromite in the concentrates can cause serious downstream processing problems and a grade of less than 3% Cr₂O₃ is sought. This constrains operating procedures and compromises optimum recovery of the PGEs.In this study, the influence of the froth phase on the recovery of chromite was investigated by changing both frother type and dosage and froth height in batch scale flotation tests. The results obtained showed that it was possible to obtain concentrates with less than 3% Cr₂O₃ content by increasing the froth height, allowing for better drainage of both entrained gangue particles and coarse particles with low hydrophobicity. At a 3 cm froth height, very low water and mass recovery were obtained and thus low entrainment. Nevertheless a small amount of chromite particles coarser than 45 μm was persistently recovered which may be attributed to the true flotation of these particles.The mechanism of chromite recovery was discussed on the basis of the difference in the appearance of the froth structure and water recovery.     

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.     

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).     

新型钼捕收剂飞瑞7#在辽宁某难选钼矿石浮选中的应用研究

飞瑞7_#是一种新型的钼矿物浮选捕收剂,它对钼矿物捕收力强并兼具起泡性能,浮选过程中能形成稳定的泡沫层。对辽宁某难选钼矿石不仅能提高钼选矿回收率并可节省起泡剂用量30%以上。     

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.     

无机盐阳离子对粉煤灰浮选泡沫稳定性的影响研究

粉煤灰中矿物组成的自然属性使得浮选脱炭体系的泡沫稳定性较差,从而影响了未燃炭的有效脱除。通过添加无机盐阳离子的方式来改变粉煤灰浮选矿浆体系的液相性质,研究了不同离子种类和含量对两相泡沫和粉煤灰浮选三相泡沫稳定性的影响,并进行了浮选验证。研究结果表明：无机盐阳离子的添加提高了泡沫的稳定性,阳离子价态越高,这种稳定作用就越明显。利用泡沫稳定性调节中的离子效应,对采自湖北黄石的粉煤灰样品进行了浮选脱炭的验证试验,结果表明：Fe3+对泡沫的稳定作用有效提高了粉煤灰的浮选脱炭效果,与空白浮选体系相比,在Fe3+浓度为3 mmol/L的条件下,浮选低炭灰烧失量由8.85%降低至5.57%,炭脱除率由41.94%提升至74.55%;与添加Fe3+的浮选体系相比,Mg2+和Na+对浮选指标的提高作用依次减弱。     

Non-ionic polyethylene oxide frothers in graphite flotation

The Kringel Mine (Woxna Graphite AB) in Hälsingland, Sweden, is one of the largest graphite flake deposits in the world with over 10 million tonnes of ore suitable for open cast mining. Concentration of crystalline graphite is carried out through a combination of flotation, gravimetric and magnetic separation. In the present study, several polyethylene oxide type frothers were evaluated as flotation frothers for the graphic ore. From (a) laboratory dynamic and equilibrium surface tension experiments, (b) froth equilibrium height measurements, (c) bench scale flotation tests and (d) plant trials, it was shown that a polyoxypropylene glycol butyl ether (MW 300 and HLB 6.5) was the most effective frother for the graphic particles. The frother was found to produce closed packed, molecular cohesive films at the air/solution interface showing high elasticity at low concentrations, which appeared to prevent bubble coalescence. The plant has been successfully using this frother as a replacement for MIBC since July 1997.