基于微气泡残留的疏水性颗粒—气泡脱附新机制研究

脱附是导致粗颗粒浮选回收率低的重要原因。为了探究疏水性颗粒-气泡间脱附行为机理,利用自 制的浮选颗粒-气泡脱附测试系统对不同疏水性颗粒的脱附过程进行观测,借助 Image-Pro Plus 图像处理软件对颗 粒-气泡间接触角、三相润湿周边变化进行测量。结果表明：颗粒脱附过程中接触角并非保持不变,而是存在明显 的接触角滞后,接触角为 67.0°、83.9°和 98.7°的 3 种疏水性颗粒在达到前进接触角 106.7°、119.3°和 128.3°后三相润 湿周边开始滑动收缩。区别于传统三相润湿周边滑动脱附机制,发现在三相润湿周边滑动阶段为了保证颗粒前进 接触角不变,不可避免地会在颗粒表面形成反向毛细颈部,且反向毛细颈部处曲率随着三相润湿周边的收缩而快 速增加,并最终在拉普拉斯压力作用下发生断裂脱附,在颗粒表面留下微气泡。同时由于三相润湿周边滑移速度 随着颗粒疏水性的增加而降低,因此反向毛细颈部处曲率增加速率随颗粒疏水性的增加而增加,导致最终颗粒表 面残留微气泡大小也随颗粒疏水性的增加而增加。     

DTAB 对石英-气泡间相互作用力的影响研究

为了研究(十二烷基三甲基溴化铵)DTAB 对石英-气泡间相互作用的 影响,采用黏附/脱附测试系统、接 触角测量仪和表面张力仪对 DTAB 体系下亲水性石英玻璃基板与气泡间相 互作用力、表面接触角以及溶液表面张力 进行了测量。 结果表明:在 DTAB 体系中,石英玻璃基板与气泡间的黏附力 /脱附力随着 DTAB 浓度的增加先增加后 减小,在 DTAB 浓度为 1 mmol/L 时,脱附力达到最大,为 129. 9 μN; 石英玻璃基板表面接触角也呈现类似的变化规 律,在 DTAB 浓度为 4 mmol/L 时,接触角达到最大,为 51. 8°,较石英 玻璃基板与气泡间黏附力/脱附力而言,接触角的 变化具有一定的滞后性。 这是由于黏附力/脱附力受石英玻璃基板表面 接触角和表面张力协同支配,在 DTAB 存在体 系下,当接触角达到最大时,溶液表面张力已下降至 35. 95 mN/m,导致 石英玻璃基板与气泡间黏附力/脱附力提前出 现下降趋势。 进一步用浮选动力学试验加以验证,浮选结果表明,当浮选体 系中加入 1 mmol/L DTAB 时可以获得精 矿产率为 97. 10%的指标。 浮选结果与黏附力/脱附力曲线得到的结果 保持一致。     

湍流场中浮选颗粒-气泡脱附行为的尺寸效应研究

湍流诱发浮选颗粒-气泡脱附已达成广泛共识,但湍流场中颗粒的脱附行为机制仍未明晰。传统离心脱附理论认为当颗粒所受离心力大于毛细力时颗粒从气泡表面脱附,忽略了颗粒重力对浮选颗粒-气泡间稳定性的影响,且未考虑不同尺寸颗粒间的脱附行为差异。采用自制的微流体通道湍流槽探索了湍流涡中不同尺寸颗粒的脱附行为,运用Image-Pro Plus图像处理软件对颗粒脱附过程的动力学参数进行测量分析。结果表明,粗颗粒(2.0 mm)质量大,颗粒在气絮体升浮阶段发生直接脱附;而中颗粒(1.0 mm)和细颗粒(0.5 mm)质量小,气泡会带动颗粒由湍流槽底部向湍流涡中心旋转迁移,同时颗粒在气泡表面高速旋转发生离心脱附。此外,颗粒稳定性分析表明传统邦德(B_O^*)模型并不能对湍流场中的颗粒-气泡气絮体稳定性进行准确判断,颗粒易受湍流涡加速或气泡振荡的影响,导致颗粒脱附时邦德数在1左右波动。     

气泡在煤炭表面的碰撞和粘附过程

煤泥浮选中,煤的可浮性与其表面润湿性质密切相关,选用表面润湿性差异较大的褐煤和焦煤为对象,研究气泡与煤炭表面碰撞过程中的三相接触周边的形成过程。分析了两种煤炭界面性质的差异,并采用I-SPEED 3高速动态摄像机记录并分析气泡与煤炭表面碰撞和黏附的微观过程。结果表明,在一定的碰撞速度条件下,气泡和煤炭表面要经过“接触-弹回-再接触”的数次碰撞过程,并最终形成气液固三相接触周边。焦煤表面与气泡经过2次碰撞后形成的铺展面积为8.2 mm2,而褐煤表面的三相接触周边形成之前经过了3次碰撞,且气泡在其表面的最终铺展面积为4.6 mm2。煤炭表面的接触角越大,三相接触周边形成的时间就越短,气泡在煤炭表面的铺展面积也越大,这从微观角度验证了浮选过程中煤炭表面疏水性对气泡矿化过程的影响。     

气泡在煤炭表面的碰撞和黏附过程

煤泥浮选中,煤的可浮性与其表面润湿性质密切相关,选用表面润湿性差异较大的褐煤和焦煤为对象,研究气泡与煤炭表面碰撞过程中的三相接触周边的形成过程。分析了两种煤炭界面性质的差异,并采用I-SPEED 3高速动态摄像机记录并分析气泡与煤炭表面碰撞和黏附的微观过程。结果表明,在一定的碰撞速度条件下,气泡和煤炭表面要经过"接触—弹回—再接触"的数次碰撞过程,并最终形成气液固三相接触周边。焦煤表面与气泡经过2次碰撞后形成的铺展面积为8.2 mm~2,而褐煤表面的三相接触周边形成之前经过了3次碰撞,且气泡在其表面的最终铺展面积为4.6 mm~2。煤炭表面的接触角越大,三相接触周边形成的时间就越短,气泡在煤炭表面的铺展面积也越大,这从微观角度验证了浮选过程中煤炭表面疏水性对气泡矿化过程的影响。     

泡沫泥饼形成机理

分析了泡沫泥饼的形成过程，其形成机理在于3个方面，即粘土颗粒间吸力和斥力的相对大小变化、聚合物吸附层对颗粒间作用力的影响以及气泡在井壁表面形成了三相润湿周边。     

煤颗粒与气泡黏附行为的试验研究

浮选微观模型认为,颗粒与气泡的黏附是实现浮选的关键步骤,对颗粒与气泡黏附规律的直接研究非常重要。采用自行设计搭建的颗粒与气泡碰撞、黏附行为测量装置,以内蒙古公乌素原煤为试验对象,直接观测了不同密度级的0.1~0.15 mm粒级煤样的黏附行为,并采用自行开发的多目标追踪软件进行分析。结果表明:煤颗粒在与气泡碰撞前会发生绕流,速度大小和方向均会改变,当煤颗粒与气泡碰撞时,煤颗粒的速度降为最低。煤颗粒在气泡表面的滑动速度先是逐渐增大,在气泡"赤道"位置处达到最大值,越过"赤道"后,煤颗粒的滑动速度逐渐减小,并最终黏附在气泡底部。煤颗粒与气泡的黏附效率随碰撞角的增大而降低,在碰撞角相同时,随煤样密度级的增大,黏附效率降低,临界黏附角减小。随煤颗粒沉降末速的增大,煤颗粒与气泡的黏附效率降低,临界黏附角减小。     

新型复合捕收剂强化细粒低阶煤浮选机理研究

低阶煤表面含有丰富的含氧官能团且孔隙发达,用传统非极性烃类油浮选低阶煤时药剂耗量大、可燃体回收率低,针对此问题,将柴油、脂肪酸及其酯类化合物按照一定比例复配,制备了一种新型复合药剂(DK１),并考察了其对低阶煤浮选的效果.通过接触角测量、诱导时间分析以及颗粒 气泡间临界脱附力测量等方法,揭示了新型复合捕收剂强化低阶煤浮选机理.结果表明:同等药剂用量下,DK１可燃体收率是柴油的２~４倍,同时精煤灰分普遍低于柴油１~４个百分点.新型复合捕收剂处理过后的煤样接触角更大,诱导时间明显缩短至１０ms以内,颗粒 气泡间跳入黏附力、临界脱 附 力 的 作 用 程 及 其 大 小 均 有 不 同 程 度 增 加.DK１的柴油与活性物质产生协同作用,有效覆盖低阶煤表面,显著提高了低阶煤的可浮性,降低了药耗,DK１药剂用量仅为柴油的１/８.     

密度对细粒煤颗粒与气泡间相对运动的影响

颗粒与气泡间相对运动的研究对浮选机理的认识十分重要,目前关于颗粒与气泡间相对运动的研究多为理论推导,试验研究比较匮乏且试验对象多为形状规则,表面性质均匀的颗粒。以内蒙古公乌素原煤为研究对象,利用自行设计搭建的试验装置研究了粒级为0.100～0.074 mm、密度级分别为-1.3,1.4～1.5和+1.7 g/cm~3的煤样与气泡间的相对运动。试验通过追踪大量煤颗粒的运动轨迹,研究了颗粒沉降阶段、运动轨迹偏离阶段和碰撞阶段中颗粒运动特征参数的变化规律。试验结果表明:颗粒当量直径均值为0.092 mm,颗粒经短暂加速后便达到沉降末速,颗粒沉降末速随颗粒当量直径和密度的增大而增大。气泡会影响颗粒的运动轨迹,同一初始沉降区间内,竖直方向上煤样轨迹偏离点到气泡的距离随煤样密度的增大而减小。静水条件下颗粒和气泡碰撞角的主分布区间为20°～50°,且碰撞区间和颗粒集中分布区间随初始沉降区间向外扩展而扩展。颗粒和气泡的碰撞角小于50°时,碰撞点处颗粒速度减小比例随碰撞角增大近似直线减小,碰撞角大于50°时,碰撞点处颗粒速度减小比例趋于平稳,低密度颗粒的速度减小量大于高密度级颗粒的速度减小量,然而差异并不明显。理论计算发现,颗粒初始沉降位置距气泡中轴较近时理论碰撞速度较小,且颗粒理论碰撞速度随颗粒初始沉降位置向外扩展而增大,与试验规律较为吻合。     

浮选中颗粒-气泡间相对运动研究进展

颗粒-气泡间相对运动的研究对浮选机理的认知至关重要,对新型浮选机的开发和提高浮选效率均具有指导意义,本文系统综述了颗粒-气泡间相对运动的研究进展。早期研究过程中,研究者忽略了颗粒和气泡性质的影响,将颗粒视为随流线运动的点,气泡视为刚性球体,利用流线方程对颗粒-气泡间的相对运动展开研究;随着认知过程的不断深入,颗粒和气泡物理化学性质的影响逐步得到了关注,研究者分别从颗粒惯性力、重力、形状和粗糙度以及气泡表面流动性等方面并展开了大量研究;颗粒-气泡间相对运动的试验研究多通过颗粒沉降法进行,研究对象由单个玻璃微珠发展为大量矿物颗粒,且出现了关于运动玻璃球与上升气泡之间相对运动的研究。研究表明,当颗粒粒度较细、密度较小时,利用流线方程对颗粒-气泡间相对运动的研究具有一定的适用性;当颗粒粒度较粗、密度较大时,需考虑正负惯性力、重力等因素对颗粒-气泡间相对运动的影响。此外,颗粒形状的不规则性会影响颗粒周围液体对颗粒的作用力,导致临界碰撞半径减小,且颗粒表面不规则的凸起会促进颗粒-气泡间水化膜的破裂,减少诱导时间,增大颗粒表面粗糙度有助于增强颗粒-气泡间的黏附强度。气泡表面的流动性可采用"滞留帽"模型进行分析,具有较好的适用性。对于颗粒-气泡间相对运动的试验研究主要采用颗粒沉降法,亲水玻璃微珠只能在气泡上半球滑行,到达气泡赤道位置附近后便离开气泡,疏水玻璃微珠会刺破颗粒-气泡间的水化膜,越过气泡赤道后会继续沿气泡表面滑行并最终黏附在气泡底部,煤颗粒与气泡的黏附效率随碰撞角和密度的增大而减小。然而目前的试验研究多集中于静水领域,对于浮选流场中颗粒-气泡间相对运动的试验研究尚需进一步探索。     

Detachment of coarse composite sphalerite particles from bubbles in flotation: Influence of xanthate collector type and concentration

The force required to detach sphalerite ore particles from air bubbles has been measured in flotation concentrates, for particles in the size range of 150–300 μm and 300–600 μm with different degrees of liberation. An electro-acoustic vibrating apparatus, that produces typical force conditions experienced in a flotation cell, was used to measure particle–bubble detachment as a function of the vibrational acceleration. Sodium isopropyl xanthate (SIPX) and potassium amyl xanthate (PAX) collectors were used in flotation, at different concentrations. At a fixed frequency of 50 Hz, the maximum vibrational amplitude at which a particle detaches from bubble was used to calculate the particle detachment force. It was shown that changes in surface hydrophobicity (contact angle), due to variations in reagent conditions have significant impact on particles detaching from bubbles. On average, detachment of particles from oscillating bubble correlated well with xanthate concentration and hydrocarbon chain length of xanthate ions. Particles (300–600 μm) with high contact angle obviously required higher force to detach from bubbles than similar particles with lower contact angle. This correlated well with the flotation response at the different reagent conditions. SEM analysis of particles after detachment showed that fully liberated particles attached to bubbles more readily and also gave higher detachment force than composite particles. Moreover larger detachment forces were observed, on average, for particles with irregular shape compared to particles with rounded shape of the same size range.     

Bubble–particle detachment in a turbulent vortex I: Experimental

The mechanics of the detachment of particles from bubbles in the flotation process in a turbulent environment are unclear. The traditional hypothesis assumes a bubble–particle aggregate is trapped inside an eddy of equivalent size, and the attached particles rotate at the same speed as the eddy. The rotational movement subjects the attached particles to a centrifugal force. It is theorised that particles detach when the centrifugal force is greater than the capillary force, but this hypothesis has not yet been experimentally proven.This work is an experimental study of bubble–particle detachment in a rotating eddy. A special experiment was designed to obtain a strong confined vortex, and bubble–particle aggregates were introduced into the cavity without destroying the vortex structure. This newly developed method, which provides a realistic analogue of the turbulent conditions in a flotation cell, is well suited to the study of an important sub-process of flotation in a turbulent field, namely, the stability of single bubble–particle aggregates.Particles can detach from bubbles by a number of ways, including inertial actions induced by rapid changes in direction, and disruption due to coalescence of colliding bubbles. In this paper, we focus on a particular mechanism, in which bubbles are observed to rotate in a turbulent vortex. Particles can be held on the surface of the bubble by surface tension, and the radial centripetal force induced by the rotation is sufficiently high, particles may detach. Experiments are described in which the process of particle detachment due to centrifugal movement, was captured by a high-speed video camera, and the necessary physical parameters, especially the rotational velocity of the particles, were extracted. For the first time, centrifugal movement of the particle on the bubble surface inside a vortex was observed, and the theory of detachment due to centrifugal forces in the turbulent field was experimentally proven.     

Poly (N-isopropylacrylamide) (PNIPAM) as a flotation collector: Effect of temperature and molecular weight

Poly (N-isopropylacrylamide) (PNIPAM), a temperature responsive polymer, was tested for its potential use as a collector in a quartz flotation system. The effect of PNIPAM on the surface characteristics of quartz particles were studied using induction time, contact angle and zeta potential measurement and analysed in terms of the probability of bubble/particle attachment and the probability of formation of stable bubble/particle aggregates. It was found that probability of bubble/particle attachment of quartz significantly increases in the presence of PNIPAM, particularly at temperatures above the lower critical solution temperature (LCST) of 32 °C. Furthermore, the probability of bubble/particle attachment increases with increasing PNIPAM molecular weight. This was attributed to the increased hydrophobicity of the quartz surface as well as the decrease in the double layer repulsion between bubbles and particles. This leads to the conclusion that PNIPAM could act as an effective collector in a flotation system.     

Role of oily bubbles in enhancing bitumen flotation

A recognized challenge in bitumen extraction is the reduced bitumen recovery when processing high-fine ores or “weathered” oil sand ores, collectively called poor processing ores. Preliminary lab tests demonstrated that bitumen flotation recovery from these ores could be greatly enhanced by using oily bubbles (air bubbles coated with a thin layer of oil or solvent) instead of air bubbles. In this study, dynamic contact angle of air/oily bubbles on bitumen surface and induction time of bitumen–air/oily bubble attachment in aqueous solution were measured to investigate the mechanisms of how oily bubbles help improve bitumen recovery and to justify the use of oily bubbles while processing poor oil sand ores. Oily bubbles showed a marginal effect on the contact angle values compared to air bubbles. However, the spreading of oily bubbles on a bitumen surface was found to be much faster than that of air bubbles. The induction time for bubble–bitumen attachment in the process water from poor processing ores was found to be much shorter for oily bubbles than for air bubbles. The reduced induction time for kerosene-coated air bubble–bitumen attachment correlates well with the improved bitumen recovery from poor processing ores using kerosene-coated oily bubble flotation technology.     

Fundamental study of reactive oily-bubble flotation

A novel concept of reactive oily bubbles (i.e., bubbles covered by a thin layer of oil containing oil-soluble collectors) as a carrier in flotation is proposed. In addition to the role of fine particle agglomeration by oily films, the surface properties of air bubbles coated with a thin oil film can be better controlled for the desired selectivity by adding certain types and concentrations of water insoluble collectors into the oil phase. Oily bubbles attain a much higher contact angle than air bubbles, ensuring a strong collecting power, favorably for floating both coarse and fine particles. The reactive oily bubble flotation can eliminate the addition of collector to the aqueous phase, avoid undesired synergetic interactions among collectors, activators, depressants and dispersants present in slurry, minimize undesired activation of gangue particles and significantly reduce the amount of collectors needed.The electrokinetics of kerosene droplets in aqueous collector solutions was measured as a function of solution pH. The results clearly showed that the surface charge and hence the surface properties of oil droplets can be finely tuned by controlling the type of the collectors to suit the desired flotation needs. The attachment of collector-containing oily bubbles on silica, sphalerite and galena surfaces was investigated with contact angle measurement. The concept of using reactive oily bubble to achieve selective flotation was demonstrated in microflotation tests.     

A study of bubble–particle interaction using atomic force microscopy

Interaction between solid particles and air bubbles is central to froth flotation. Measurement of such interaction forces has only recently been possible with the invention of the atomic force microscopy (AFM). In this paper, the AFM colloidal probe technique was used to measure hydrodynamic interaction forces between a solid sphere attached to an AFM cantilever and an air bubble placed on an AFM piezoelectric stage at different approach speeds. Strong repulsive forces due to the hydrodynamic interaction were established and quantified for both hydrophobic and hydrophilic particles, and bubbles in deionised water and 1 mM KCl aqueous solutions. No surfactants were used. In the case of hydrophobic spheres, strong attraction between the surfaces, in addition to the repulsive hydrodynamic force, was observed, leading to the rupture of the intervening water film due to submicroscopic bubbles and the attachment of the particle to the air bubble at relatively large separation distances, which were of the order of 500–2000 nm. In the case of hydrophilic spheres, the rupture of the intervening water film and the attachment of the particle to the air bubble did not take place. An analysis of the AFM data was carried out to obtain the interaction force and relative separation distance. Theoretical hydrodynamic force calculation shows agreement with experimental data for larger separation distances. Deviations at shorter distances are related to the deformation of air–water interface due to the particle approach and surface forces.     

Quantifying particle pick up at a pendant bubble: A study of non-hydrophobic particle–bubble interaction

To study bubble interaction with non-hydrophobic particles an imaging technique has been developed to quantify particle pick up at a pendant bubble by measuring the bubble–particle attachment angle (BPA) made by the particle bed on the bubble. The technique was verified by correlating pick up mass against BPA. Pick up of alumina was shown to correlate with difference in alumina and bubble zeta potential supporting an electrostatic model of interaction with non-hydrophobic particles. Pick up also correlated with contact angle (Washburn method) indicating the electrostatic force is sufficient to establish a solid–air interface.