Prediction of the metallurgical performances of a batch flotation system by image analysis and neural networks

It is now generally accepted that froth appearance is a good indicative of the flotation performance. In this paper, the relationship between the process conditions and the froth features as well as the process performance in the batch flotation of a copper sulfide ore is discussed and modeled. Flotation experiments were conducted at a wide range of operating conditions (i.e. gas flow rate, slurry solids%, frother/collector dosage and pH) and the froth features (i.e. bubble size, froth velocity, froth color and froth stability) along with the metallurgical performances (i.e. copper/mass/water recoveries and concentrate grade) were determined for each run. The relationships between the froth characteristics and performance parameters were successfully modeled using the neural networks. The performance of the developed models was evaluated by the correlation coefficient (R) and the root mean square error (RMSE). The results indicated that the copper recovery (RMSE = 2.9; R = 0.9), concentrate grade (RMSE = 1.07; R = 0.92), mass recovery (RMSE = 1.94; R = 0.94) and water recovery (RMSE = 3.07; R = 0.95) can be accurately predicted from the extracted surface froth features, which is of central importance for control purposes.     

Froth transport characterization in a two-dimensional flotation cell

A study of the froth bubble transport in a two-dimensional (2D) flotation cell was performed. Experiments were developed as a 2 × 2 factorial design, in which the effect of superficial air rate (1.2–1.8 cm/s) and froth depth (2–4 cm) on the froth transport for a two phase (air–water) system was characterized.Using image analysis techniques, bubble residence times, air recovery, bubble path and bubble size increase through the froth were obtained. This information was complemented by froth surface velocity measurements using the Visiofroth system.It was found that bubbles transported from the pulp–froth interface up to the overflow, showed a minimum residence time for bubbles entering the froth near the lip wall. Also, the air-recovery significantly changes in a range of 7–20% at different operating conditions.Higher residence times promoted bubble size increase by coalescence for bubbles transported from the interface. Conversely, for lower residence times, a smaller increase in bubble size was observed.     

Process mineralogy studies of Corrego do Garimpo REE ore, catalao-I alkaline complex, Goias, Brazil

Corrego do Garimpo is described as a lateritic rare earths (REE) deposit related to hydrothermal alteration of dolomitic carbonatitic rocks. Although the deposit has been known since the sixties, all the previous mineral dressing attempts to concentrate the REE bearing minerals resulted in unsatisfactory outcomes. Process mineralogy studies of bulk and borehole samples were fundamental to understanding the ore's behavior and to the development of an unusual physical concentration process.The ore comprises a medium to very fine-grained soil material with large amounts of secondary (autigenous) minerals. Monazite, the essential REE bearing mineral, occurs as microcrystalline aggregates, sometimes presenting colloidal textures, which are frequently associated with iron oxide—hydroxides and quartz. Since these aggregates are extremely friable, the monazite crystallites are mainly associated with the −20 μm size fraction.These particular characteristics supported the development of an unconventional mineral processing method for monazite based on disaggregation, followed by scrubbing and hydrocyclone classification operations. Three volumetric samples and 27 borehole samples, comprising four ore types, have been studied. The attained final products, −10 μm, were further submitted to leaching tests, simulating chemical processing for the REE sulphuric extraction at low temperature.     

Adsorption of copper sulphate on PGM-bearing ores and its influence on froth stability and flotation kinetics

Copper sulphate is used as an activator in the flotation of base metal sulphides as it promotes the interaction of collector molecules with mineral surfaces. It has been used as an activator in certain platinum group mineral (PGM) flotation operations in South Africa although the mechanisms by which improvements in flotation performance are achieved are not well understood. Some investigations have suggested these changes in flotation performance are due to changes in the froth phase rather than activation of minerals by true flotation in the pulp zone. In the present study, the effect of copper sulphate on froth stability was investigated on two PGM containing ores, namely Merensky and UG2 (Upper Group 2) ores from the Bushveld Complex of South Africa. Froth stability tests were conducted using a non-overflowing froth stability column. Zeta potential tests and ethylenediaminetetraacetic acid (EDTA) tests were used to confirm the adsorption of reagents onto pure minerals commonly found in the two ores. The results of full-scale UG2 concentrator on/off copper sulphate tests are also presented. The UG2 ore showed a substantial decrease in froth stability in the order of reagent addition: no reagents > copper > xanthate > copper + xanthate, while Merensky ore showed a slight decrease. It was shown through zeta potential measurements that copper species were to be found on plagioclase, chromite, talc and pyrrhotite surfaces and through EDTA extraction that this copper was in the form of almost equal amounts of Cu(OH)₂ and chemically reacted copper ions on the Merensky and UG2 ore surfaces. In certain cases, the presence of copper sulphate and xanthate substantially increased the recovery, and therefore the implied hydrophobicity, of pure minerals in a frothless microflotation device. It was, therefore, proposed that increases in hydrophobicity beyond an optimum contact angle for froth stability, were the cause of instabilities in the froth phase and these were found to impact grade and recovery in a full-scale concentrator. Differences in the extent of froth phase effects between the different ores can be attributed to differences in mineralogy.     

Development of an index for the floatability of Indian coal fines

Batch flotation experiments were carried out on four different Indian bituminous coal samples in the size -74 μm at various levels of variables. It has been noticed from the results that at any flotation time, the yield of concentrate Y (t) follows a linear relationship of the following form with the amount of water W(t) reporting to the concentrate. Y(t)=F_w(t)+E_w(t)·W(t)The intercept value F_y(t) which is termed as the true flotation component of yield when hypothetically no water reports to the concentrate has been found to increase with flotation time as given by the equation F_w(t)=F_w(∞)·[1−exp(−k_w·t)]Based on these observations, an index called “floatability index (FI)” has been proposed to quantify the response of coals towards froth flotation. This index is defined as The floatability index varies from 0 to 100. Consequently, the higher the value of the index for any coal, the better is its response towards flotation. The floatability index has been found to be specific for a given coal and is independent of process variables like reagent dosages, solid content of feed slurry and flotation time.     

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.     

河南某钼矿的选矿工艺试验研究

河南某钼矿采用泡沫浮选技术处理富集辉钼矿,考察了浮选粒度、捕收剂种类及用量、氧化矿硫化处理和抑制剂等因素对浮选效果的影响,通过试验确定闭路工艺流程。试验结果表明,粗精矿钼品位1.994%、回收率为66.63%。该工艺流程可以有效回收辉钼矿。     

Upgrading titanium bearing Na-feldspar by flotation using sulphonates, succinamate and soaps of vegetable oils

Large reserves of feldspar ores exist in the Aegean region of Turkey. Unlike conventional ores, the main impurity in some of these deposits is titanium. In this study, the results of testwork carried out to determine flotation conditions for efficient separation of titatium bearing minerals from two different feldspar ores from the area are presented. The study commenced with mineralogical examination which indicated that the main titanium bearing mineral in the ore was rutile. Another titanium mineral, sphene, was also present in relatively small quantities. In the tests, the effects of particle size, pH, collector types and their amount were tested.The results showed that efficient separation of titanium bearing minerals could be achieved by oleate flotation at around pH 5, after grinding the ore down to 100% −180μm. Oleate provided results superior to sulphonates and succinamate. Equivalent success was obtained by the use of collectors prepared from locally available vegetable oils. Of the five oils tested, sunflower and cotton seed oils produced the most efficient separation.     

Selective transport of attached particles across the pulp–froth interface

A technique for determining the recovery of attached particles across the froth phase in flotation that relies on measuring the rate at which bubble–particle aggregates enter the froth is used to investigate the selectivity of attached particles across the froth phase. Combining these measurements with those of other techniques for determining the froth recovery of attached particles provides an insight into the different sub-processes of particle rejection in the froth phase. The results of experiments conducted in a 3 m³ Outokumpu tank cell show that the detachment of particles from aggregates in the froth phase occurs largely at the pulp–froth interface. In particular it is shown that the pulp–froth interface selectively detaches particles from aggregates according to their physical attributes.     

A new collector for rare earth mineral flotation

A new collector for bastnaesite flotation - modified hydroxamic acid (MOHA) has been developed through several years laboratory research. The experimental results of flotation of pure bastnaesite mineral and rare earth ores, and the application experience in flotation plants showed that MOHA is an efficient collector for bastnaesite flotation. MOHA has stronger collector ability and higher selectivity compared to the other commonly used collectors. Through the measurements of zeta-potential, adsorption and infrared adsorption spectrum and in terms of the electronegativity theory of reagent groups, the flotation mechanism has been discussed. It was concluded that the adsorption of MOHA on bastnaesite surfaces is chemical adsorption in nature through three oxygen atoms in the polar group of MOHA chelating the surface Ce(III) of bastnaesite to form a pentagon-cycle chelate: O---C=N---O---Ce(III)---). Additionally, the chemisorption is accompanied with the multilayer and non-homogeneous physical adsorption of the MOHA molecules. The MOHA adsorption equation at the surfaces of bastnaesite can be expressed as: Γ = 6.76×10⁻²C^1/1.02, while the adsorption rate constant k is: k = 2.64×10⁵min⁻¹mol⁻¹m².     

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。     

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.     

An experimental study of the recovery of hydrophilic silica fines in column flotation

This paper presents results of tests performed to investigate the effect of gas rate (1.2–2.5 cm/s), hydrophilic fines content (5–20% w/w silica) and froth depth (10–30 cm) on fines recovery in a laboratory-scale flotation column operating without wash-water addition and absence of floatable particles. A model was developed based on the entrainment coefficients presented by [Trahar, W.J., 1981. A rational interpretation of the role of particle size in flotation. International Journal of Mineral Processing 8, 289–327], which describes the mass contribution of the different size classes to the solids recovered in the concentrate. The entrainment model of [Zheng, X., Johnson, N.W., Franzidis, J.P., 2006. Modelling of entrainment in industrial flotation cells: water recovery and degree of entrainment. Minerals Engineering 19, 1191–1203] was also tested. The results show both models described well the dependence of the mass flow rate of hydrophilic solids in the concentrate.     

粗细粒级差异化给矿对浮选柱选别性能的影响

粗细粒级矿物具有不同的浮选特性,浮选柱主要应用于精选作业的细粒级矿物分选,对粗颗粒矿物回收率较低,限制了浮选柱的应用。在泡沫层分选理论的基础上,以纯石英矿物(纯度大于99%)为代表矿样,将其分成150~280μm和-15μm粗细粒级两个组分,采用Ф100 mm×2 000 mm浮选柱开展试验考察粗细粒级差异化给矿对选别性能的影响。在一个试验中将粗细粒级矿物混合给入浮选柱泡沫层之下进行常规浮选,在另一个试验中将粗细粒级矿物差异化给入浮选柱泡沫层之上和泡沫层以下分别进行泡沫层分选和常规浮选。试验对比结果表明,粗细粒级差异化给矿提高了浮选柱精矿回收率,对粗颗粒矿物回收效果提升更为显著。     

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.     

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。     

The effect of flotation and parameters for bioleaching of printed circuit boards

Waste electrical and electronic equipment (WEEE) is currently one of the fastest growing waste streams in the world. Typical for WEEE is the high content of valuable and precious metals, as well as harmful contaminants like halogens, flame retardant chemicals and plastics. Currently, WEEE treatment and metal recovery methods are imperfect, polluting and energy intensive. In this paper, novel treatment possibilities are outlined for printed circuit boards (PCB) utilizing both the flotation separation technique and acid bioleaching. Flotation, conducted after crushing and sieving of PCB, produced two fractions: metal-rich concentrate, which is more suitable for pyrometallurgical treatment than untreated PCB, and metal-poor froth suitable for acid bioleaching. It was seen that especially low pH (1.6), high initial Fe²⁺ concentration (7.8 g/l) and low PCB froth concentration in the bioleaching solution (50 g/l) were beneficial for the rapid and selective dissolution of copper. With these parameters, 99% of copper was solubilized from PCB froth in bioreactor treatment, with Cu (6.8 g/l) and Fe (7.0 g/l) being the only major metallic elements in bioleaching solution.     

淀粉与氧化铁矿物的应用及其作用机理的研究进展

浮选工艺在处理低品位难选赤铁矿的选矿中,具有精矿产品杂质含量少,药剂成本低,经济效益好等优势,与强磁选相结合的选矿工艺对赤铁矿的选矿效果比较理想。目前浮选工艺特别是反浮选在处理低品位难选赤铁矿的实际生产中被广泛应用,大大提高了选矿效率和选厂的经济效益。淀粉作为赤铁矿浮选中的高效、无毒、可降解、来源广、成本低的高分子有机抑制/絮凝剂已在实际生产中广泛应用。由于具有以上优点,淀粉在选矿中的应用前景广阔,但目前对天然高分子有机药剂特别是多糖类如淀粉在氧化铁矿表面的作用机理的论述较少,因此研究淀粉与氧化铁矿的作用机理具有一定的实际意义。     

The effect of galvanic interaction on the behaviour of the froth phase during the flotation of a complex sulphide ore

A literature review has shown that the chemical effects of grinding media on the flotation of real ores, especially those containing pyrite, are still not understood adequately. Many studies have been conducted on isolated minerals or in solutions only, and transport phenomena in the froth phase have generally been ignored in studies on galvanic interactions. A complex ore containing galena, sphalerite, chalcopyrite and significant quantities of magnetite, pyrrhotite and pyrite was used in batch flotation tests to study this problem. Metallic iron powder was added in different quantities to a ceramic ball mill in order to simulate the use of mild steel grinding media in flotation tests aimed at selectively floating chalcopyrite.An oxygen-saturated pulp milled in the presence of iron yielded the best recovery of chalcopyrite and copper-lead selectivity. Milling under a nitrogen atmosphere in the absence of metallic iron resulted in poor copper-lead selectivity. The galvanic interaction caused by the presence of iron yielded a stable, well-drained froth with low ratios of solids/water recovery and larger bubbles in the froth. However, milling in the absence of iron caused an extremely brittle froth with very fine bu bubbles, high recoveries of low grades of sulphur. In contrast with the improvement in the copper recovery and copper-lead selectivity obtained when the pulp was pre-aerated after milling in the presence of iron, no significant increase in the copper grade was observed after extensive pre-aeration when milling occurred in the absence of iron. The unsatisfactory flotation results in the absence of iron could be explained by the enhanced floatability of iron-bearing gangue minerals, which rupture films and suppress froth stability owing to bubble-overloading.     

改善赤铁矿磨矿效果的试验探索

为了提高选矿厂的浮选效率,获得较好的铅锌浮选指标,对选矿工艺流程进行考察,分别研究了矿浆pH、回水、原矿品位对铅锌浮选指标的影响。结果表明,矿浆pH值对铅浮选指标影响较小,矿浆pH过高抑制锌的浮选,铅锌粗选矿浆pH值为11左右时,铅锌浮选品位与回收率均最高;原矿铅锌品位增大铅锌精矿品位与回收率均显著增大,尾矿铅锌品位基本不变;在磨矿全采用回水时造成铅浮选泡沫发粘,分选效果差,铅浮选回收率下降,铅锌浮选中矿量大,使得浮选操作难控制;经分析铅锌浮选尾矿中多为连生体,需细磨铅锌才充分单体解离。