粒度大小对赤铁矿和石英浮选分离的影响

通过浮选试验、DLVO理论计算、聚焦光束反射测量（FBRM）等研究了油酸钠浮选体系下粒度大小对赤铁矿和石英浮选分离的影响。人工混合矿浮选试验表明,窄粒级粗粒或中等粒级的赤铁矿?石英混合矿（CH&CQ和MH&CQ）的浮选效果较好,其中CH&CQ和MH&CQ的分选效率分别为85.49%和84.26%,明显高于全粒级混合矿（RH&RQ）的分选效率74.94%;但窄粒级的细粒赤铁矿?石英混合矿（FH&FQ）的浮选效果则较差,其分选效率只有54.98%。浮选动力学试验表明,赤铁矿的浮选速率和回收率不仅与赤铁矿的粒度有关,还受石英粒度的影响,细粒脉石矿物石英会降低赤铁矿的浮选速率和回收率。DLVO理论计算表明,当矿浆pH值为9.0时,石英与赤铁矿颗粒间的相互作用力为斥力,此时细粒石英很难“罩盖”在赤铁矿表面并通过这种“直接作用”的方式抑制赤铁矿浮选,这也与聚焦光束反射测量（FBRM）的测定结果基本一致;颗粒?气泡碰撞分析表明,在浮选过程中细粒石英可能通过“边界层效应”的方式跟随气泡升浮（夹带作用）,影响赤铁矿颗粒与气泡间的碰撞及黏附,从而降低了赤铁矿的浮选速率和回收率。      

The Effect of Bubble Size on Fine Particle Flotation

Abstract

Expressions for the probability of collision (P_c) and adhesion (P_a) have been derived for fine particle flotation by calculating the trajectory of particles as they flow past a bubble in streamline How. Three different flow regimes have been considered in the present work, i.e., Stokes, potential and intermediate. For the intermediate flow conditions in which most flotation operations are carried out, the particle trajectories have been determined using an empirical stream function derived in the present work. For the case of a very hydrophobic coal sample, the values of the probability of collection (P) determined experimentally have been found to be in close agreement with the theoretically predicted P_c values over a range of bubble and particle sizes

The expression for P_a has been derived by determining the time it takes for a particle to slide along the surface of a bubble after collision. It has been assumed that the bubble-particte adhesion occurs when the sliding time is equal to or exceeds the induction time, which varies with the particle hydrophobicity. P_a is shown to be a function of particle size, bubble size and induction time. The values of P_a predicted in the present work are in good agreement with the results of microflotation tests conducted on a coal sample.     

碳酸钠对白钨矿自载体浮选的影响及机理

-10 μm白钨矿的浮选回收率低, 导致大量白钨矿损失于尾矿中, 造成资源浪费, 而载体浮选是提高-10 μm白钨矿回收率的有效方法之一.根据粒级以及粒级组成对白钨矿浮选的影响, 通过浮选试验、理论计算和仪器检测等方法研究了-10 μm细粒级白钨矿的自载体浮选, 同时研究了载体比例、载体含量和碳酸钠对白钨矿自载体浮选的影响.研究结果表明, 油酸钠为捕收剂时, 在合适的载体粒度和载体比例下, 自载体浮选是提高-10 μm白钨矿回收率的有效方法, 碳酸钠可强化白钨矿的自载体浮选, 扩大载体比例和载体粒度范围.机理研究表明, 白钨矿      

Interactions between a Small Bubble and a Greater Solid Particle during the Flotation Process

ABSTRACT

The interaction between bubbles and solid particles is an important mechanism in many industrial processes and flotation is a significant component of the most utilized applications. While flotation of mineral ores deals with fine particles and larger bubbles, the aim of this review is to focus on the opposite case; the interaction between smaller bubbles and larger particles encountered mostly in plastic flotation. Plastic flotation seems to be one of the appropriate methods for separating plastics, which is necessitated by increasing plastic consumption and the growing need to recycle. The first part of the article focuses on the problem of the collision of a bubble with a particle, both spherical and planar. The collision efficiency is discussed. The second part is devoted to the problem of liquid film rupture and the creation of the three-phase contact line. The third and final part focuses on the problem of the three-phase line expansion and the effect of surfactants on the resulting bubble stability.     

EFFECTS OF PARTICLE SIZE ON THE SINTERING KINETICS IN TUNGSTEN POWDER

Abstract

An experimental study has been made of the effects of initial particle size on sintering kinetics in tungsten powder within the temperature range 1100–1500°C. Particle size, compacting pressure, sintering time and temperature all influence the rate of sintering. Isothermal changes in density and volume have been measured. The results indicate grain-boundary diffusion as the mechanism principally responsible for material transport in the case of particle sizes <4 μ Surface diffusion appears to bethe mechanism of material transport in compacts with particle sizes of 14– 16 μ The temperature-dependence of the rate of sintering is characterized by activation energies of 101± 2 and 72± 2 kcal/mole for fine particles (< 4 μ) and coarse particles (14–16 μ), respectively.     

Thermodynamic and Kinetic Flotation Criteria

Abstract

Flotation thermodynamics and notation kinetics are discussed and compared with chemical thermodynamics and chemical kinetics. While chemical thermodynamics can predict whether a reaction will take place under a given set of conditions (temperature and pressure), and can also predict the direction in which the equilibrium will be shifted in response to variation in these parameters, flotation thermodynamics can predict how likely it is for the mineral particle and gas bubble to attach in a moment of their collision. While thermodynamics can predict the probability of particle-to-bubble attachment, it cannot predict the rate of this process, for the energy barrier, G_attach, opposing particle-to-bubble attachment, is not interrelated with the free energy change accompanying the attachment

The thermodynamic (Δ G < 0) and kinetic (τ_i; < τ_c c) flotation criteria are examined by a study of the effect of frothers on flotation. Various hypotheses that explain how the frother can affect flotation rate are discussed with emphasis on unsolved problems.     

Water model study on inclusion removal from liquid steel by bubble flotation under turbulent conditions

Abstract

Inclusion removal from liquid steel by bubble flotation under turbulent conditions is analysed using a water model. Turbulence is realised by impeller stirring in a water containing vessel. First, the effects of variables such as filter pore size, gas flowrate, NaCl concentration, and stirring intensity on bubble size are investigated. Second, particle removal by bubble flotation is studied using the water containing vessel system. The results indicate that particle removal rate by bubble flotation is controlled by non-first order kinetics. The factors affecting the particle removal rate constant k ₁ are discussed and a final empirical equation is derived as follows: -dc/dt = k ₁ c^1·3665 and k ₁ = A(d _p/d _B)^2·65?0·104 Q _g^1·630, where c is particle number density, t is time, A is a constant parameter, d _p and d _B are the particle and bubble diameter respectively, ? is the turbulent energy dissipation rate, and Q _g is the gas flowrate.     

赤铁矿的自载体作用及对浮选的影响

通过单矿物浮选试验、光学显微镜分析、E-DLVO理论计算、团聚动力学分析等研究了油酸钠浮选体系下赤铁矿浮选过程中的自载体作用。单矿物浮选试验表明，粗粒赤铁矿（?106 + 45 μm）的可浮性较好，当油酸钠用量超过15 mg·L?1时，回收率可达到90%以上，而细粒赤铁矿（?18 μm）的浮选回收率、浮选速率则较低；当粗?细赤铁矿中粗粒和细粒的质量近似相等时，粗粒的“自载体”效果最强，浮选回收率增加的也最明显，但粗粒过量则会导致粗粒对细粒赤铁矿浮选的强化作用减弱。光学显微镜分析和E-DLVO理论计算表明，粗?细赤铁矿颗粒间的相互作用能高于细粒赤铁矿间的相互作用能，与细粒赤铁矿相比，粗?细赤铁矿间更容易发生团聚，这也是粗粒能够强化细粒赤铁矿浮选（自载体作用）的主要原因。但过量的粗粒赤铁矿会增强其浮选过程中的“磨削、剪切”作用，导致粗粒的“自载体”效果减弱，浮选回收率降低。      

Current PM Literature for Engineers and Users

Abstract

Fine tin powders were produced in a pilot plant gas atomiser. Nitrogen gas at 1·56 MPa pressure was used as the atomising agent in a ‘confined design’ nozzle which operated vertically upwards. A range of metal flowrates from 0·864 to 1·425 kg min^?1 was studied at a melt temperature of 450°C. Powders were sized using dry sieving down to 45 μm and wet sieving for smaller sizes. The Sauter mean diameter of the powders varied from 9·01 to 10·28 μm, depending on the rate of production. The size distribution was bimodal (albeit not very well defined) with the peak separation at ～44 μm. In the fine size range, particles were spherical, while those in the coarse range were more elongated or irregular in shape and free of satellites. Comparison of the tin powders with copper powders from another study, AA 2014 aluminium alloy powders, and magnesium and zinc powders from previous work showed that the differences in mean diameter and standard deviation are small among these common metals at a given volumetric production rate. This confirms the overriding importance of liquid metal volume flowrate under fixed gas flow conditions in gas atomisation, while the actual physical properties of the liquid playa secondary role. Although surface tension is secondary to volume flowrate in importance for controlling particle size, the study has shown that a liquid metal with lower surface tension and viscosity than AA 2014 alloy, together with a higher density, yields finer particles. PM/0667A     

Effect of particle size distribution on recovery of coarse chalcopyrite and galena in Denver flotation cell

Abstract

The flotation recovery by particle size of single mineral chalcopyrite and galena was studied in a Denver flotation cell, using sodium dicresylthiophosphate (DTP) and sodium isopropyl xanthate (SIPX) as collectors and polypropylene glycol (PPG) as a frother. The study was extended to very coarse particle size (up to 1·6 mm). Froth stability was also measured in parallel to the batch flotation tests, in a specifically designed froth stability column, following the Bikerman approach. It is shown that particles up to 850 μm can be floated successfully, provided they are liberated and hydrophobic. However, the recovery of both chalcopyrite and galena was strongly influenced by the overall particle size distribution, decreasing sharply as the fraction of fines (?106 μm) in the feed also decreased. Rheology measurements showed negligible differences in pulp viscosity, and therefore in the collection zone hydrodynamics, between the different conditions tested. Froth stability, on the contrary, decreased as the feed particle size distribution became coarser. Correlation was found between the amount of fines in the pulp, froth stability and flotation recovery. The recovery of mineral particles is critically dependent on froth stability, which in turn is highly influenced by the overall particle size distribution of the feed material. For these reasons, the study also suggests that it is not possible in batch flotation to determine the rate and recovery of the coarse particle size fractions floating them independently from the fine size fractions.

Dans une cellule de flottation de Denver, on a étudié la récupération par flottation en fonction de la taille de particule d’un minéral unique de chalcopyrite ou de galène, en utilisant du dicrésyle thiophosphate de sodium (DTP) et de l’isopropyle xanthate de sodium (SIPX) comme agents collecteurs et du polypropylène glycol (PPG) comme agent moussant. On a étendu l’étude à la taille de particule très grossière (jusqu’à 1·6 mm). On a également mesuré la stabilité de la mousse en parallèle aux essais de flottation discontinue, dans une colonne de stabilité de la mousse spécialement conçue, d’après l’approche de Bikerman. On montre que l’on peut faire flotter avec succès des particules ayant jusqu’à 850 μm, à la condition qu’elles soient libres et hydrophobes. Cependant, la récupération, tant de la chalcopyrite que de la galène, était fortement influencée par la distribution globale de la taille de particule, diminuant sévèrement à mesure que la fraction de particules fines (?106 μm) dans l’alimentation diminuait. Les mesures de rhéologie montraient des différences négligeables dans la viscosité de la pulpe et ainsi dans l’hydrodynamique de la zone de collection, parmi les différentes conditions évaluées. Au contraire, la stabilité de la mousse diminuait à mesure que la distribution de la taille de particule de l’alimentation devenait plus grossière. On a trouvé une corrélation entre la quantité de particules fines dans la pulpe, la stabilité de la mousse et la récupération par flottation. La récupération des particules minérales dépend, de façon critique, de la stabilité de la mousse qui, à son tour est hautement influencée par la distribution globale de la taille de particule du matériel d’alimentation. Pour ces raisons, l’étude suggère également qu’il n’est pas possible, en flottation discontinue, de déterminer la vitesse et la récupération des fractions de taille de particules grossières, en les faisant flotter indépendamment des fractions de taille fine.     

Dissolved gas method of generating bubbles for potential use in ore flotation

Production and use of dissolved air bubbles were investigated with the purpose of improving the recovery of fine particles in ore flotation processes.The rate and extent of air dissolution were studied under different conditions of pressure, temperature, liquid volume, and gas-solid contact. The process of bubble formation by pressure release was also examined. Assessments made through dissolved oxygen measurements indicated that dissolution of air and the release of dissolved air could be achieved within a 1-minute period. Flotation tests carried out on a ?37 μm magnetite ore sample demonstrated superior results with dissolved gas bubbles compared to conventional bubbles.     

Hydrodynamics of Bubble-Mineral Particle Collisions

Abstract

This chapter surveys the hydrodynamic interactions between particles and bubbles in flotation. Some new approximate equations are given for collision efficiency. It is shown that collision processes of particles with bubbles are less effective than sliding processes because of their short duration and the strong deformation of the bubble at the collision point. Methods are suggested to estimate collision and sliding times. During contact between a particle and a bubble, the just forming thin liquid film must drain off and rupture. Therefore, possible ways of calculating film drainage time are discussed. Furthermore, possible experimental methods to determine these quantities are briefly described and recent experimental results presented.     

浮选过程中颗粒--气泡黏附作用机理及研究进展

系统分析总结了浮选过程中颗粒与气泡的黏附概率模型、EDLVO理论、颗粒-气泡集合体的受力分析、影响因素分析和颗粒-气泡黏附的研究进展.基于接触时间、感应时间的方法和能量势垒的方法,分别从动力学和热力学的角度分析总结了黏附概率模型,并从动力学和热力学的角度解释了颗粒大小、气泡大小、颗粒疏水性、颗粒表面粗糙度和溶液pH对黏附概率的影响,对静态环境和湍流环境中颗粒-气泡集合体进行了受力分析,颗粒和气泡的黏附力有毛细作用力、液体静压力和浮力,静态环境中的脱附力只有重力,但是湍流环境中的脱附力还包括振荡力和离心力.很多研究学者利用先进的仪器和检测手段对颗粒-气泡的黏附做了大量的研究,取得了大量研究成果.颗粒-气泡黏附作用过程相当复杂,试验研究时简化了作用条件,目前理论不能满意解释黏附过程,需要结合实际进行更深层次、更全面的研究.      

WEAR AND FRICTION STUDIES OF NICKEL–TUNGSTEN CARBIDE–GRAPHITE COMPOSITES

Abstract

Wear and friction studies have been carried out on pressed and sintered composites of 75–95% theoretical density. Carbonyl nickel and tungsten carbide, both with a particle size of 5 μm, and natural crystalline flake graphite with an approximate size of 1·1 μm were used. The wear specimens were run against a rotating (100 rev/min) steel cylinder. The wear-resistance correlates well with the ratio of the volume fraction of tungsten carbide to that of graphite (WC/graphite); there is a minimum in weight loss at a ratio near unity. This effect is explained in terms of powder coating with graphite during blending, which affects grain-boundary formation and grain growth during sintering; supporting metallographic evidence is given. The wear-debris particle size produced is related to wear; the wear rate increases with increasing particle size. Residual porosity in the materials reduces wear-resistance. The wear rate does not correlate with hardness or coefficient of friction; the results of wear tests in oil or water are very similar to those for tests run in air.     

Mechanical alloying of Cu–SiC materials prepared with utilisation of copper waste chips

Abstract

The aim of this work was to study the structure and particle size of copper based composite materials reinforced with a high content (15–35 wt-%) of silicon carbide and prepared by mechanical alloying in the high energy planetary mill. Raw materials consisted of grinded copper chips with a size of <5000 μm and reinforcing particles with an initial size of 10 μm. Duration of milling was 20–80 min. It was shown that the formation of Cu–(15–25 wt-%)SiC composites occurred successfully. With an increase in the silicon carbide content of above 25 wt-% (48 vol.-%), the efficiency of mechanical alloying was decreased. The average size of composite particles was ～20 μm.     

PowderMet2009: prospects improving after automotive debacle

Abstract

A homogeneous powder and binder distribution in the green body in powder injection moulding (PIM) is important. In the present study, the mould filling model of PIM has been developed, based on the multiphase fluid theory, viscosity model of feedstock and powder-binder drag force model. The particle Reynolds number is influenced by the particle size and density, resulting in the different drag force between powder and binder. Furthermore, the varied velocity of binder and powder will be obtained with numerical calculation of the continuity equations, leading to the change of green body homogeneity. CFX was used to simulate the mould filling in PIM. The results showed that the homogeneity of green bodies was relative to the filling patterns, which varied with different powder densities. The powders were not suitable for PIM when the particle size was bigger than 20 μm, and the fine powders were beneficial to improve the homogeneity.     

Characterisation of nickel alloy powders processed by spark plasma sintering

Abstract

In this study, nickel alloy powders were consolidated by spark plasma sintering. Experiments were performed between 700 and 750°C temperature range under 50 MPa pressure with holding times from 5 to 10 min. In addition to these main spark plasma sintering parameters three different heating rates ranging from 100 to 235°C min^?1 and two different particle size ranges (75–106 μm narrow size distribution and ?45 μm wide size distribution) were used for the experiments. After sintering, the sliding wear behaviour of the samples was investigated. The results revealed that the density of the material increased with raising the sintering temperature and holding time. However, heating rate and particle size also played an important role in the densification and these parameters were investigated in detail.     

Column Froths

Abstract

Column froths are discussed in terms of structure, effect of variables on gas holdup profiles, cleaning (rejection of entrained particles), selectivity (between hydrophobic species), carrying capacity and froth stability

The froth is shown to be stabilized by wash water and to have two sections, one near the interface where gas holdup increases rapidly to about 74% and an upper one where change is less rapid. The upper section is subject to mixing by the wash water

In cleaning an important factor is gas rate. Pulp water recovery, and hence entrainment, increases with gas rate: a superficial gas rate (volumetric gas rate per unit time per column cross-sectional area) less about 2 cm/s is recommended. Deep froths (>100 cm) do compensate for high gas rates to some extent. Increasing bias water rates (e.g., >0.3 cm/s) does not compensate for the effect of high gas rates but rather introduces excessive turbulence in the upper section of the froth and loss of cleaning action

Carrying capacity is revealed as a major limiting factor for processing fine particles (<30 μm). Carrying capacity (as mass solids/unit time/unit column cross-sectional area) appears to depend linearly on particle size. Some design and operating consequences of carrying capacity are outlined

Brief reference is given to reports of froth instability. No clear conclusion regarding the effect of solids is reached.     

Transient liquid phase sintering of high density Fe3Al using Fe and Fe2Al5/FeAl2 powders Part 1: Experimentation and results

Abstract

High density Fe₃Al was produced through transient liquid phase sintering, using rapid heating rates of greater than 150 K min^-1 and a mixture of prealloyed and elemental powders. Prealloyed Fe₂Al₅/FeAl₂ (50Fe/50Al, wt-%) powder was added to elemental iron powder in a ratio appropriate for producing an overall Fe₃Al (13·87 wt-%) ratio. The heating rate, sintering time, sintering temperature, green density and powder particle size were controlled during the study. Heating rate, sintering time and powder particle size had the most significant influence upon the sintered density of the compacts. The highest sintered density of 6·12 Mg m^-3 (92% of the theoretical density for Fe3Al) was achieved after 15 minutes of sintering at 1350°C, using a 250 K min^{- 1} heating rate, 1-6 μm Fe powders and 5·66 μm alloy powders.

SEM microscopy suggests that agglomerated Fe₂Al₅/ FeAl₂ particles, which form a liquid during sintering, are responsible for a significant portion of the remaining porosity in high sintered density compacts, creating stable pores, larger than 100 μm diameter, after melting. High density was achieved by minimising the Kirkendall porosity formed during heating by unbalanced diffusion and solubility between the iron and Fe₂Al₅/FeAl₂ components. The lower diffusion rate of aluminium in the prealloyed powder into the iron compared with elemental aluminium in iron, coupled with a fast heating rate, is expected to permit minimal iron-aluminium interdiffusion during heating so that when a liquid forms the aluminium dissolves in the iron to promote solidification at a lower aluminium content. This leads to a further reduction in porosity.