Froth flotation of scheelite – A review

Froth flotation of scheelite has regained new focus since the 2010s and research regarding floatability and reagents has made great progress over the years. The main objective was and remains the selective flotation of scheelite from other calcium-bearing minerals, in particular calcite, fluorite and apatite. Due to similar properties, most attempts have limited success or only specific application(linked to a type of ore or a location). This article aims at reviewing all general physical-chemical information on froth flotation of scheelite, including electrokinetic properties, influence of p H and already existing reagents as well as ones still under examination. It appears that chelating or mixed collectors and modified versions of sodium silicate and quebracho hold great promise for scheelite flotation, while the use of said depressants and/or promoters seems inevitable.     

Nano-microbubble flotation of fine and ultrafine chalcopyrite particles

As is well known to mineral processing scientists and engineers, fine and ultrafine particles are difficult to float mainly due to the low bubble-particle collision efficiencies. Though many efforts have been made to improve flotation performance of fine and ultrafine particles, there is still much more to be done. In this paper, the effects of nano-microbubbles (nanobubbles and microbubbles) on the flotation of fine (−38 + 14.36 μm) and ultrafine (−14.36 + 5 μm) chalcopyrite particles were investigated in a laboratory scale Denver flotation cell. Nano-microbubbles were generated using a specially-designed nano-microbubble generator based on the cavitation phenomenon in Venturi tubes. In order to better understand the mechanisms of nano-microbubble enhanced froth flotation of fine and ultrafine chalcopyrite particles, the nano-microbubble size distribution, stability and the effect of frother concentration on nanobubble size were also studied by a laser diffraction method. Comparative flotation tests were performed in the presence and absence of nano-microbubbles to evaluate their impact on the fine and ultrafine chalcopyrite particle flotation recovery. According to the results, the mean size of nano-microbubbles increased over time, and decreased with increase of frother concentration. The laboratory-scale flotation test results indicated that flotation recovery of chalcopyrite fine and ultrafine particles increased by approximately 16–21% in the presence of nano-microbubbles, depending on operating conditions of the process. The presence of nano-microbubbles increased the recovery of ultrafine particles (−14.36 + 5 μm) more than that of fine particles (−38 + 14.36 μm). Another major advantage is that the use of nano-microbubbles reduced the collector and frother consumptions by up to 75% and 50%, respectively.     

Study on Non-Collision Mineralizing Mechanism of Froth Cyclone

On the basis of the mineralizing mechanism of froth cyclone, this paper expounds that the froth cyclone flotation process is accomplished in a limited centrifugal field. The main feature of air bubble mineralizing in the froth cyclone is a synthetic mineralizing process, of which the non-collision mineralization of minute air bubble separated out dominates, supplemented with the collision mineralization. Moreover, this paper points out that the hydrophobic separated out and centrifugal force strengthen the selectivity of fine coal particle, accelerate the flotation speed and improve the slime recovery.     

Destabilising persistent coal froth using silicone oil

Persistent froth is becoming more and more common in coal and mineral flotation plants and presents safety and operational challenges. No effective method has been developed to destabilise persistent froth. As a new initiative, this study examined the structural difference between persistent foam and coal froth, based on which a solution was developed to maximumly destabilise coal froth. Destabilisation test, oscillatory rheology measurement and scanning electron microscopy (SEM) analysis indicated that the coal froth was more stable than the foam due to the formation of thin capillaries and tightly arranged coal particles on bubble surfaces. Although 107 µm silicone oil droplet could completely destabilise the foam at 2 mmol/L concentration, it only destabilised less than 50% coal froth even at 6 mmol/L concentration. To maximumly destabilise the coal froth formed by −38 and −20 µm particles, 24 and 18 µm silicone oil droplets were required to pass through the thin capillaries and enter the bubble films, respectively. However, smaller silicone oil droplets could not bridge the bubble films to destabilise coal froth and therefore a critical droplet size occurred depending on the size of particles stabilising the froth.     

澳大利亚微细粒级磷矿浮选试验

对澳大利亚某地微细粒级磷矿进行浮选试验,将水玻璃、碳酸钠和调整剂L2添加点前移,与矿石一起磨矿充分混匀后,在矿浆质量分数为19%时进行浮选.试验结果为精矿P2O5品位30.56%,精矿产率88.02%,回收率97.01%.     

细粒煤重介质离心分选脱硫试验研究

在重介质条件下利用Falcon离心重力分选系统,研究了-500μm不同窄粒级南桐细粒煤的脱硫降灰效果.采用可燃体回收率、脱灰率、脱硫率、脱硫效率4个指标,对比分析了Falcon重介离心分选和常规浮选对南桐细粒高硫煤各粒级的分选效果,结果表明:对于-500μm细粒级煤,脱灰率低于常规浮选,而其余3个指标均高于浮选.125μm是分选效果的显著分界粒度,500～125μm粒级煤的脱硫率、脱灰率高于浮选,而可燃体回收率低于浮选.-125μm粒级煤的脱硫率、脱灰率低于浮选,而可燃体回收率高于浮选.     

纳米泡提高细粒煤浮选效果的研究

泡沫浮选槽中微细粒级低效浮选的原因是颗粒与气泡的碰撞概率低,而粗颗粒浮选回收差的原因是大量颗粒从气泡上脱落,采用文丘里管产生纳米泡,研究了利用纳米泡提高细粒煤浮选效果的机理,结果表明:纳米泡浮选过程中,纳米泡会优先聚集在疏水性颗粒表面,通过调整给料速度、捕收剂添加量等浮选条件,可燃体回收率提高10%～30%,纳米泡起到了辅助捕收的作用,并可以减少药剂用量1/3～1/2.     

沉积变质型黄梅磷灰岩工艺矿物学研究

利用矿物自动定量分析系统（AMICS）及偏光显微镜对黄梅沉积变质型磷灰岩开展了系统的工艺矿物学研究,并进行了浮选验证试验。研究结果表明:该磷灰岩中主要磷矿物为磷灰石（23.57%）,主要脉石矿物为石英（26.32%）和钾长石（26.51%）,次要的脉石矿物为白云石（12.12%）和方解石（3.68%）;且磷灰石、石英、钾长石的嵌布粒度较粗,只有少量白云石和方解石以浸染的方式嵌布在胶磷矿内部;当矿石粒度度小于0.074 mm占57.71%时,磷灰石、石英和钾长石基本实现单体解离（解离度＞80%）;随后采用一粗一精浮选试验进行验证,发现在该磨矿粒度下,可获得91.84%的浮选回收率,且精矿中P₂O₅品位为35.77%。     

Effect of depressants on flotation separation of magnesite from dolomite and calcite

The flotation separation of magnesite from calcium-containing minerals has always been a difficult subject in minerals processing. This work studied the inhibition effects of carboxymethyl cellulose(CMC),sodium lignosulphonate, polyaspartic acid(PASP) and sodium silicate on flotation behaviors of magnesite, dolomite and calcite, providing guidance for the development of reagents in magnesite flotation.The micro-flotation results showed that among these four depressants, sodium silicate presented...     

Nanobubble generation and its applications in froth flotation (part Ⅱ):fundamental study and theoretical analysis

Froth flotation is a commonly employed technology to improve the quality of raw coal and minerals. Coal and minerals particle size and surface hydrophobicity are two main parameters that affect three key steps in froth flotation process: particle-bubble collision, adhesion, and detachment. This paper fundamentally investigated the effects of nanobubble on coal and phosphate flotation. It has been found that the presence of nanobubble in flotation pulp could widen the coal and phosphate flotation particle size range, increase the particle surface hydrophobicity, and thus improve the coal and phosphate froth flotation recovery.     

Nanobubble generation and its applications in froth flotation(part Ⅱ):fundamental study and theoretical analysis

Froth flotation is a commonly employed technology to improve the quality of raw coal and minerals.Coal and minerals particle size and surface hydrophobicity are two main parameters that affect three key steps in froth flotation process:particle-bubble collision,adhesion,and detachment.This paper fundamentally investigated the effects of nanobubble on coal and phosphate flotation.It has been found that the presence of nanobubble in flotation pulp could widen the coal and phosphate flotation particle size range,increase the particle surface hydrophobicity,and thus improve the coal and phosphate froth flotation recovery.     

中低品位磷矿重介质选矿试验

对宜昌丁东磷矿进行重介质选矿试验.当分离密度为2.96 g/cm^3时,沉物P2O5品位达30.86%,回收率55.61%,MgO为0.95%,可获得合格精矿;当分离密度为2.70 g/cm^3时,浮物可抛去17.35%左右的尾矿,可作中低品位胶磷矿预选作业,若再用浮选,即可获得优质精矿.     

Explaining surface interactions for common associated gangues of rare earth minerals in response to the oxalic acid

In the flotation of rare earth minerals(REMs), oxalic acid is reportedly acting both as a depressant and p H modifier. Although results of testing have established the significance of oxalic acid in the flotation process, its specific role in either the recovery or selectivity of REMs over their common gangue minerals is not well understood. Pulp p H reduction trials with alternative acids have not shown the same effect on the REMs recovery or the depression of gangue phases. This work studies the effect of oxalic acid on the surface of common REMs gangue minerals(quartz and carbonates(dolomite and calcite)) in a series of conditioning tests. Gangue surface analyses by time of flight secondary ion mass spectroscopy(TOFSIMS) indicate that oxalic acid inhibits the transfer of secondary ions generated during the conditioning process from one mineral to another. In this regard, the oxalate anion acts to fix ions in solution through chelation, limiting their participation in surface adsorption.     

Two-step flotation recovery of iron concentrate from Donganshan carbonaceous iron ore

The flotation of pure and natural carbonaceous iron ore samples in the oleate flotation system was investigated. Starch can depress hematite effectively in a wide pH range, but cannot depress siderite efficiently in neutral conditions. The flotation recovery of pure hematite, siderite, and quartz in the oleate-starch-CaCl₂ system is significantly different when the slurry pH varies from 4 to 12. A novel two-step flotation process was developed for the separation of iron concentrate from Donganshan carbonaceous iron ore through which the siderite concentrate is first recovered and the high quality hematite concentrates with relative high iron recovery can be obtained in the second step flotation. The siderite concentrate may be utilized directly or undergo further concentration steps to increase iron grade.     

Nanobubble generation and its applications in froth flotation(part Ⅳ): mechanical cells and specially designed column flotation of coal

Coal is the world's most abundant fossil fuel.Coal froth flotation is a widely used cleaning process to separate coal from mineral impurities.Flotation of coarse coal particles,ultrafine coal particles and oxidized coal particles is well known to be difficult and complex.In this paper,the nanobubbles' effects on the flotation of the varying particle size,particle density and floatability coal samples were evaluated using a bank of pilot scale flotation cells,a laboratory scale and a pilot scale specially designed flotation column.The parameters evaluated during this study include the flow rate ratio between the nanobubble generator and the conventional size bubble generator,the superficial air velocity,collector dosage,frother concentration,flotation feed rate,feed solids concentration,feed particle size,and the superficial wash water flow rate,etc.The results show that the use of nanobubbles in a bank of mechanical cells flotation and column flotation increased the flotation recovery by 8%～27% at a given product grade.Nanobubbles increased the flotation rate constants of 600～355,355～180,180～75,and 75～0 microns size coal particles by 98.0%,98.4%,50.0% and 41.6%,respectively.The separation selectivity index was increased by up to 34%,depending on the flotation feed characteristics and the flotation conditions.     

新型柱浮选泡沫输送装置及固液两相流动特性

针对高含气率、高黏性柱浮选泡沫输送的需要,设计了一种新型柱浮选泡沫输送装置,并进行了固液两相流动特性模拟.结果表明,漩涡多靠近叶片工作面,其方向与叶轮旋转方向相反;叶轮内各流道压力分布较为均匀,叶轮中心区域为低压力区;颗粒直径越大,叶片工作面和轮缘处分布的颗粒越多,磨损程度越重;颗粒浓度越大,流体的全速度越高,叶轮出口附近处颗粒速度梯度越大,叶轮受局部磨损程度越重.基于数值模拟的优化设计结果表明,采用后倾叶片、扩大出料管径和增加出料管数量,有利于改善输送效果.     

煤泥浮选测控系统的研究

浮选自动化在我国多年来俳徊不前,一直采用根据入浮煤浆中的干煤泥量来确定加药量的前馈控制方法,而不直接以产品的数质量指标作为控制目标,导致浮选生产效率较低。针对上述问题,研究了浮选工艺参数的检测方法,开发了浮选浆位仪和煤浆测灰仪,设计了浮选计算机控制系统,它根据煤浆测灰仪旁线检测的精煤灰分,运用模糊控制技术,通过调整浮选药剂添加量和浮选机浆位,来实现浮选过程的反馈控制,工业性试验表明,煤浆测灰仪的性能指标接近国外先进水平,煤泥浮选测控系统在淮北选煤厂的现场使用,使浮选生产在精煤灰分合格的前提下,得到了较高的产率,并降低了药剂用量,从而保证选煤厂高效率地运行。     

Prospects of utilization of waste dumped low-grade limestone for iron making: A case study

Low grade dumped limestone sample having high silica of 8.1%, 36.8% CaO, and 3% Al_2O_3 has been studied with the aim to reduce the silica level to below 3% for its utilization in iron making. Beneficiation study of the sample was initiated with desliming of the feed sample of -100 μm to remove the siliceous ultrafine particles and to improve the feed quality. Flotation study was carried out by column flotation technique varying the collector dosage, superficial air flow velocity and froth depth to assess their effect on silica reduction and CaO recovery. It was observed that increased collector dosage and superficial air velocity increases the recovery of CaO, and increase in the froth depth reduces the mass flow and silica content in the concentrate. The best result was found at 1.25 cm/sec superficial air velocity, 25 cm froth depth, 1.25 kgpt collector dosage and concentrate assayed 47.3% CaO, 2.8% silica with 72% CaO recovery.     

Studies of benzyl hydroxamic acid/calcium lignosulphonate addition order in the flotation separation of smithsonite from calcite

Flotation separation of smithsonite from calcite is difficult due to their similar surface properties. In the present study, a reagent scheme of depressant calcium lignosulphonate (CLS) and collector benzyl hydroxamic acid (BHA) was introduced in the flotation of smithsonite from calcite. Microflotation tests revealed that the efficient flotation of smithsonite from calcite could only be obtained with the addition order of BHA before CLS, which was opposite to the widely-used order that adding depressant prior to the collector. The zeta potential measurements indicated that BHA selectively adsorbed onto smithsonite surface, then not allowed the CLS adsorption onto the smithsonite surface rather than calcite surface because of the steric hindrance, thereby the smithsonite surface remained hydrophobic while calcite surface became more hydrophilic after the addition of CLS. As a result, the calcite flotation was completely depressed while the smithsonite flotation recovery was still in high value, leading to the optimal flotation separation performance.     

偏心轴搅拌槽内的层流流场特性

针对搅拌槽内处理层流状态下高黏度流体时混合效率偏低的现象,提出一种偏心轴(轴结构为曲轴)搅拌方式。首先以纯度为99%的甘油为介质,传统的二叶平桨为研究对象,对直径0.3 m的搅拌槽内的层流流场进行数值研究。中心搅拌时速度模拟结果与试验结果对比,验证了所建模型及模拟方法的可靠性。研究发现,与中心搅拌相比,偏心搅拌和偏心轴搅拌所产生的流场结构是非对称的;相同转速下,偏心轴搅拌相比中心搅拌时流体的槽内整体的体积加权平均速度增大了约68%,功率准数比中心搅拌增加了约15.3%;偏心轴搅拌对槽内速度的提升,扩大了流体扰动范围,对提高槽内流体混合效率具有一定的优势。