Chapter 12 Equipment for interfacial separation

646 CHAPTER 12

12.EQUIPMENT FOR INTERFACIAL SEPARATION 12.1. INTERFACE GENERATING DEVICES 12.1.1. BUBBLE GENERA TORS

As mentioned above, in air-liquid interface separation it is necessary to produce lots of small bubbles which scatter evenly in the separation vessel. The main methods of producing bubbles include: (1) mechanical agitation; (2) generating bubbles by bubble generators; (3) releasing air from solution; and (4) producing bubbles by electrolysis.

A. Microporous-medium type bubble generators. The bubble generator is made of various microporous media, through which compressed air is made to pass. The media are canvas hoses, porous rubber tubes, nylon tubes, porous ceramic tubes or microporous plastic tubes. They have been used in pneumatic flotation machines. Since the canvas hose is liable to clog and not strong enough, it has been replaced by a porous rubber tube, microporous ceramic tube or microporous plastic tube. The microporous plastic tube has been widely used because it is very strong and resistant to wear, corrosion, and blinding. Fig.12.1 shows the states of generation of bubbles produced by compressed air passing through a microporous medium with different frother concentration or without frother addition. It is evident that addition of frother leads to generation of lots of highly-dispersed micro bubbles. The frother concentration larger than 20 mg/L can produce air bubbles of narrow size distribution with the diameter smaller than 0.5 mm. However, the coalescence takes place during the bubbles ascending process. Nevertheless, the size of the bubbles still remains less than 1.0 mm.

B. Air-water-jetting type bubble generators In order to overcome the microporous bubble generator's shortcomings, such as clogging and scaling, air-water-jetting type bubble generators have been developed, as shown in Fig 12.2 (a) and (b). In these generators, compressed air from a nozzle is mixed with water, and then jetted into small bubbles via a distribution head or nozzles.

647 C. Air-jetting type bubble generators (Glembotskii et al, 1981) Fig.12.3 shows an air-jetting type bubble generator. It consists of an air-guide tube and a special nozzle on its top end. The nozzle is made of rubber. Air is pressed into the air-guide tube by an air compressor and jetted via the nozzle. The compressed air is then scattered into small bubbles by the action of friction force and eddy flow. This bubble generator was used in deep-cell "supercharged" flotation machines (see Fig.12.3 (a)). The baffle plates located at the two sides of the air-guide tube divide the cell into an aeration zone and a flotation zone. A great difference in pulp density between the two zones usually causes a circulation of pulp flow from top to bottom. In this repeated circulation, a part of air dissolved in water rises with pulp from bottom to top and is released into microbubbles from water due to the reducing pressure.

0.3 0.2

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(b) C,, 10 /5 =,

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06

0.5

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0.4 0.3 0.2

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(a)

r ,,,/20 5

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/ 0.5

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1 1.5 2.0 Diameter of Bubbles, db, mm

2.5

Fig.12.1 Relationship between bubble fractions S and frother concentration Cs in the pneumatic flotation machine (taken from Hienisch, R. and von Szantho, E., Aufber. Techn., Nr. 9, 1972, 551-560) a). Measured directly above the bubble generator (1+ 1cm); b). Measured at the high lever 20+lcm above the bubble generator

648

Co).The USBMICominr

type bubble generator

Fig. 12.2 Tow air-water jetting type bubble generators A slit-type bubble generator (see Fig.12.4) (Klassen,1963) is similar to the above bubble generators. Compressed air is jetted to the stator consisting of curved blades through the slits between a cone liner bush and a rubber ring via an air-guide pipe, and thus lots of bubbles are formed. At a slit of 0.75mm and a pressure of (7.8~9.8)x 104 Pa, fast flowing of air and friction effect between air and aerating parts lead to a more uniform aeration, hence obtaining a better airliquid interface.

649

(a). Air flow pattern;

(b). Nozzle

Fig. 12.3 Air-jetting type bubble generator

A---A

AI

~! ~ k ' ~ . - 4 1 :

IA

Fig.12.4 Slit type bubble generator 1. Air guide pipe; 2. Cone liner bush; 3" A cylinder for adjusting slit 4. Rubber ring; 5. A stator consisting of curved blades

D. Pulp-air-mixing type aerators

650 Two pulp-air-mixing type aerators, which have been used in the pneumatic machines (Luttrell,1993; Finch,1995), are illustrated as Fig.12.5 (a) and (b). Both aerators generate bubbles by shearing. In the Microcel TMcolumn aerator, Shearing is achieved by forcing pulp and air on the blades of an in-line static mixer; while in the EKOFLOT cell aerator, pulp is forced through a constricted opening, reaching a velocity of 4-6 m/s, and shears the air (introduced at right angles from a slot) into fine bubbles.

slurry

gas

gas

bubble - slurry dispersion

(a) The EKOFLOT cell aerator

gas

slurry

bubble- slurry dispersion

(b) The MicroeelTM aerator Fig. 12.5 Pulp-air-mixing aerator E. Cyclone-jetting type aerators (Hu, 1983)

651 As shown in Fig.12.6, this aerator consists of a cone nozzle (2), a mixing chamber(3), an air inlet pipe(l), and a cyclone(4). In the aeration process, when pulp is pressured ((19.6~24.5)x 104 Pa) and jetted by the nozzle at about 20 m/s, a negative pressure in the mixing chamber is formed and air is sucked into the mixing chamber via the inlet pipe. The sucked air is rolled by the pulp and jetted by the cyclone. In this aerator, air is crushed into small bubbles by mechanical friction. In addition, a sudden reduction in pressure when the pulp is jetted by the cyclone helps to release air into microbubbles from pulp. Therefore, this aerator is cost-effective. 12.1.2. A GITA TORS

In the interface separation, a strong agitation is necessary for suspending particles and dispersing reagents. The process can be conducted in an agitation vat or tank with various agitators. The common agitators are shown in Fig.12.7 and Fig.12.8. The blade-type impeller produces mainly a rotary flow in circular direction, the turbine-type impeller mostly gives rise to a radiate flow in radial direction, whereas the propeller-type impeller chiefly generates an up-and-down convective circulation flow in axial direction ( Oshima ). Since the propeller-type impeller can produce an up-and-down convective circulation flow beneficial to suspension of solid particles, it is usually used to agitate soliquoid. To prevent formation of eddy current and suction of air around the central shaft, baffle plates are installed around the tank. They can cut the fluid thrown out by the impeller into turbulence.

1

f

44_

Fig. 12.6 Cyclone-jettingtype aerator 1. Air inlet pipe; 2. Cone nozzle; 3.Mixing chamber; 4. Cyclone

652

Blade type

Propeller typer

Turbine type Fig. 12.7 Impellers

I

|1

I I

Blade type

Turbine type

Propeller type

Fig. 12.8 Relation between a impeller and fluid flow pattern Figs. 12.9 and 12.10 show two new types of agitators" a high-dispersancy type agitator and an axial-flow type agitator (Saitou, 1987). The high-dispersancy type agitator is equipped with three inclined blades fixed at the lower part inside a cylinder sleeve. There is an outer cylinder in a given distance around the agitating shaft. There are openings on the side of the outer cylinder. The rotation of the impeller at a high speed can produce a down axial flow. Liquid above the impeller is drawn down. A part of the liquid is

653 discharged to the bottom. The other part is discharged through the openings on the side of the outer cylinder and pulverized by the action of strong shear force. Therefore, the high-dispersancy type agitator is highly efficient in mixing and suitable for dispersion and emulsification. To prevent suction of air, its agitating impeller should approach the tank bottom as closely as possible.

Fig.12.9 A high-dispersancy type agitator

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-

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Fig. 12.10 An axial-flow type agitator

654 The axial flow-type agitator is similar to the above agitator. But the former has baffle plates at the upper and lower parts of its cylinder sleeve. The baffle plates are fixed to prevent formation of eddies and suction of air. An axial circulation flow can be produced by high speed agitation. With the development of automation, serialization and miniaturization of agitating process, a pipe-type agitating device without agitating tank has come out. One of the agitating devices is a static mixer which has been widely used in chemical industry (see Fig.12.11). In this mixer, several blades are twisted at an angle of 1800and fixed crisscross in a pipe. When fluid is passing through the pipe, uniform mixing and agitation can be achieved by the cutting and shearing effect of the twisted blades. In a given length, the fluid is repeatedly twisted, thereby achieving continuous mixing and agitation of fluid-fluid, fluidair, and fluid-solid. Though the static mixer has no rotating parts, it can complete its mixing and agitation by the flow of fluid. However, in operation, a pressure loss must be continuously compensated for. Since the mixing is a static operation, the loss in pressure is small. Therefore, the static mixer is an effective agitating device. In addition, it is characterized by simple structure, low cost, convenient operation and maintenance, and easy automation (Oshima; Ye, 1988; Zhou, 1985; Mineral Processing Division, Tangshan College of Engineering and Technology, 1987).

12.1.3. OIL- WATER EMULSIFYING DEVICES (BEIXER, 1964) Oil-water emulsification is an important method of producing oil-water interface (i.e. liquid-liquid interface). The equipment includes mainly mixers, colloid mills, supersonic emulsifiers, and static mixers. flowing direction

Fig.12.11 A static mixer

655 A. Mixers

A mixer is similar to a conventional agitator, but its rotating speed is higher. It uses various types of agitating impellers. There are two types of mixers, i.e. a simple type and a complex type. The former consists of a single high speed propeller and the latter consists of propellers, cutters, mixing blades, stator, and rotor (see Fig. 12.12). The mixer is used only for rough emulsification and producing coarse emulsion. Further emulsification can be achieved by other emulsifying devices, such as a colloid mill.

t,J

i~

cutter

-

tank

. cutter

i/.,t

blade

~

[]

blade

stal

rotor

grinding unit

Fig. 12.12 A complex mixing emulsifier B. Conventional colloid mills

A conventional colloid mill consists mainly of a stator and a rotor with their smooth surfaces or rough surfaces formed by vertical or horizontal lines. The gap between the stator and the rotor is adjustable (in some cases the minimum distance is 25 gm). High speed rotation of the rotor within the stator (1000~2000 r/rain) produces a strong shearing force which makes the fluid emulsified. A vertical colloid mill and its work principle is shown in Fig. 12.13 (Stein, 1996).

656 Inlet

Slator with axial 1~[ adjustment 9

Rotor ~/

Slator

///./.~ \ \

X/i/i/i/ill

~ Onv,n a I ,~,,~S~~oa/~~~/ S tator

Grinding gap

Rotor

~

~

~

Fig. 12.13 Schematic arrangement of on-line colloidal mill

The test results (batch emulsification) of emulsifying kerosene and diesel oil by a W4-type colloid mill (see Table 12.1) are shown in Table 12.2 (Han, 1987), with the emulsifying time being 15 seconds. Tablel2.1 The specifications of two colloid mills Items Adjustable range of a microsection, mm Power, kw Rotating speed, r/min Inlet pipe, mm Outlet pipe Microsection diameter, mm Overall dimension, mm weight, kg

Type W3 0.005-1.5 7.5 2920 G 6.35 G1 145 650x300x350 100

Type W4 0.005-1.5 3 2820 G 6.35 G1 140 600x300x320 96

657 Tablel2.2 The test results (batch emulsification) of emulsifying kerosene and diesel oil Oil

Ratio of oil to water (by weight)

Results

Examination by microscope

, Static examination Mixing state Releasing oil (%) after one hour sixteen hour

Kerosene

1:10 1:20 1:30 1:50 1:80

Nearly uniform particles, 4-8~tm: 90% Nearly uniform particles, 4~8ktm: 90% Uniform particles, 4~8~m: 90% Uniform particles, 4~8~tm: 90% Uniform particles, 4~8~m: 90%

Releasing Releasing Mixing Mixing Mixing

1.2 0.8 0.6 0.3 0.2

Diesel

1:10 1:20 1:30 1:50 1:80

Not uniform particles, 6--101am: 50% Not uniform particles, 6~ 10gm: 80% Nearly uniform particles, 2-~6~tm: 80% Nearly uniform particles, 2~6~tm: 80% Nearly uniform particles, 2~6~tm: 80%

Releasing Releasing Mixing Mixing Mixing

14.2 6.9 5.0 2.6 2.4

C. Ultrasonic emulsifiers

An ultrasonic emulsifier can disperse one fluid into another fluid by ultrasonic cavitation in fluid. The fluid is sometime pressed and sometime drawn by the influence of the cavitation, thus forming voids, i.e. so-called "cavitation bubbles". When the cavitation bubbles are broken, several thousand atmospheric pressures can be delivered. Such high pressures will certainly bring about various mechanical effects (including shearing effect) which make one fluid dispersed in another fluid. In addition, these effects can produce intensive vibration energy which increases the collision probability between oil beads. Therefore, at a given frequency, emulsification can be achieved. Further, low temperature and addition of emulsifying agents are favourable for emulsification. An ultrasonic homogenizer is shown in Fig.12.14 (Edwards, 1985). The pressed slurry (about 150x105 Pa) is pumped through a specially constructed aperture to obtain a high speed. This efflux jets on a ultrasonically vibrating leaf to induce highly developed cavatition. This equipment is efficient for emulsification and dispersion. Fig.12.15 shows the emulsification results of kerosene in water using a laboratory ultrasonic emulsifying device. It can be seen that in the presence of an emulsifying agent most of emulsified kerosene beads are below 2~tm (Dai, 1986).

658

Fig. 12.14 Ultrasonic homogenizer

loo

90

70 80

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Emulsified particle size, l.tm

Fig. 12.15 The results o f ultrasonic emulsifying of kerosene 1. Kerosene +Naol+CH3(CH2)6CH2OH 2. Kerosene+Naol 3. Kerosene

6

659 D. Static m i x e r s

Apart from as a mixing agitator, a static mixer can be used as an oil-water emulsifying device. The emulsifying test was carried out using the static mixer by Shanghai Research Institute of Chemical Technology (Shanghai Research Institute; Ye,1988). The static mixer for the test is a 20.5 mm-dia, stainless steel pipe, in which a 20 mm-dia, mixing unit is fixed. The mixing unit is made of hard ripple aluminium sheet. Fluid is transported by a gear pump. The test flowsheet is shown in Fig. 12.16. In the test, kerosene, water, and emulsifying agent are put into the tank in the proportion of 3:1:0.08 by weight, and manually agitated so that they can not be laminated. Finally they are conveyed into the mixer, in which they are mixed into an emulsified product. The results show that at the same speed, the longer the mixer, the smaller the particle. To shorten the mixer, the tests were carried out using two gear pumps in series. Two mixers are 2.0m and 1.5m long respectively. The test results are shown in Table 12.3 (Shanghai Research Institute of Chemical Technology). Table 12.3 The test results approaching an actual production process No.

13-1 13-2 14-1 14-2

Bead size ~tm 13.2 2.53 7.9 2.86

Length m (ace) 2 3.5 2 3.5

Linear s p e e d m/s 1.18 1.18

gear pump

Fig. 12.16 A test flowsheet

Throughput m3/h 1.42 1.2 1.42

ta k

660 It can be seen that when the fluid passes through a given distance, static mixer can disperse liquid drops into micron size fractions. Since viscosity of the fluid will increase with decreasing size o f liquid drops, static mixer, as an emulsifier, needs to be supplied with pressure(accumulation) of several million Pas.. Table 12.4 and 12.5 show comparative results o f a static mixer with an agitator. Tablel2.4 Comparative results between a static mixer and an agitator Items

Dynamic mixer (agitator)

Static mixer

1 m3high speedbelt agitatingenamelpot High speed agitator 1400r/min, 10kw Batch 0.428 6.7 Large Difficult Difficult Large

Equipment ~20mm static mixer(meters) Auxiliary equipment Two gear pumps Operation Continuous Yield, t/h 1.05 Average size, pm 2.86 Noise Small Seal Well Maintenance Easy Floor space Small

Table 12.5 Comparison between various emulsifying devices Items

Static mixer

Colloid mill

Agitating tank

Output power,kJ/1

0.588

52.2

0.575

7.11

10.0

53.6

Average size, lam Operation Maintenance Dispersing mode Rolled bubble Distribution Investment in equipment

Continuous Zero Plug flow 0 Narrow Medium

Batch Wear of shaft Full mixing

Batch Bearing, bush Full mixing

Much Narrow

Much Wide

Large

Small

the the the a the

661 From Table 12.5, it is clear that the static mixer can be used as an oil-water emulsifying device to replace an agitating tank or colloid mill. It is an ideal emulsifying device due to its good emulsifying result, simple structure, energysaving, and convenient maintenance. 12.2. SEPARATION EQUIPMENT 12.2.1. FLOTATION MA CHINES

Since the advent of the flotation process, many different flotation machines have been developed, commercialised, and faded. In general, flotation machines can be classified into two distinct groups: pneumatic and mechanical machines (Wills, 1997), although there are different methods of classification in the literature (Zaman, 1989; Young, 1982). Pneumatic machines either use air entrained by turbulent pulp addition, or more commonly air either blown in or induced, in which case the air must be dispersed by various ways. Mechanical machines are characterised by a mechanically driven impeller which agitates the pulp and disperses the incoming air into small bubbles in the pulp. 12.2.1.1 Mechanical flotation machines. Mechanical flotation machines dominate the mineral industry worldwide. The earlier commonly used machines are the Denver cell, the Agitair flotation machine, the Wemco cell, and the Warman flotation cell. Nowadays, various mechanical flotation machines, each of which is claimed to have its own characteristics, are manufactured throughout the world (Brewis, 1996; 1991). While the mechanical flotation designs differ in detail between manufacturers, the internal hydrodynamic characteristics fall one of the two general flow categories shown in Fig.12.17 (a) and (b). The former is characterised by a mechanical mixing zone located in the central tank region, for the self-induced type mechanical flotation machine in which the depression created by the impeller induces air, while the latter in the lower region of the cell, for the "supercharged" type mechanical flotation machine where air is introduced via an external blower (Degner, 1988). Mechanical flotation machines may be designed with "cell to cell" tank structure, which is characterised by an intermediate partition and a weir between two cells and individual cell feed pipe, and "open-flow" tank structure in which there are not the intermediate partition, weir, and individual feed pipe. Most of the flotation machines now in use are of the open-flow type, as they are much better suited to high throughputs and easier to maintain than cell to cell type.

662 (AP): AIR PATH (PCP): PULP CIRCULATION PATH (M): MECHANICAL PHASE MIXING ZONE (S): SEPARATION ZONE (FR): FROTH REMOVAL AIR FROM ATMOSPHERE

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(a) Self-induced type cell

An~ FROM

II

(b) Supercharged type cell

Fig. 12.17 Mechanical flotation machine hydrodynamics

Some significant developments and refinements of mechanical flotation machines have been made in the past decades. The most pronounced evolution is the increase in flotation cell capacity, with corresponding reduction in capital and operating cost, particularly where automatic control is incorporated. In 1950, large machines were 1.35 m 3 in volume. In 1989, the largest volume was 85 m 3. But now 142 to 200 m 3 cells are used in industry ( Brewis, 1996; Suppliers news, 1997; Clifford, 1998 ). Other improvements in recent years include the introduction of new type impellers (such as the Wemcol+l mechanism and the OK agitator), the introduction of froth washing and froth crowding ( e.g. in the Outokumpu OK HG tank cell and the Wemco-Leeds cell) (Finch,1995), and the modification of tank geometry (such as U-shaped or cylindrical design). 12.2.1.1.1 Self-induced type mechanical flotation machines A. XJ flotation machines

663 The schematic drawing of the XJ flotation machine is shown in Fig.12.18. It consists of a group of two tanks. The 1st tank is a suction tank with a pulpsuction pipe. The 2nd tank is a free-flow tank without a pulp-suction pipe. There is an intermediate partition between the two tanks. In operation, when pulp is drawn into the centre of a stationary hood via the pulp-suction pipe and thrown out by the centrifugal force from the impeller, a negative pressure is created between the impeller and the stationary hood. Under the negative pressure, ambient air is sucked in via an air inlet pipe, mixed intimately with pulp, and finally thrown out by the impeller along the guide blades attached to the stationary hood, with air flow being sheared into small bubbles. XJ flotation machines are made and widely used in China to treat a variety of ores (Xia, 1985).

Fig. 12.18 The schematic drawing of the XJ flotation machine B. W e m c o Flotation cells

Fig.12.19 shows the sketch of the Wemco flotation cell. It was derived from the Fagergren flotation cell. By simplification, the original squirrel-cage and stator consisting of several parts are developed into a "1+1" rotor-stator assembly (see Fig.12.20). The cell can achieve good mixing, aerating, and agitating results due to a great circulation of pulp below the rotor. The rotation of the rotor creates a negative pressure between the blades of the rotor, so that air is drawn to the center of the rotor from top to bottom, whereas pulp is sucked to the center from bottom to top (see Fig.12.19). At the center, air flow and pulp flow are mixed, and thrown out to the stator by the rotor at high

664 tangential and radial velocities. Many perforated bands encompassing the stator change the tangential flow into radial flow to throw the resulting pulp-air mixture onto all sides of the tank. Thus micro mineralised bubbles are formed. The mineral-laden bubbles in the cell overflow by gravity from one side or double sides, and the amount can be adjusted by the baffle plates (Han, 1987).

Fig. 12.20 The rotor and stator

665 Wemco flotation cells are used most widely in the world. It is also a leading manufacturer of large flotation equipment made in sizes up to 160 m 3. The recent refinements can be seen from the Wemco SmartCell and the WemcoLeeds cell shown in Figs.12.21 and 12.22. Apart from combining the Wemcol+l mechanism, the SmartCell features a cylindrical tank which improves air dispersion and surface stability, with a conical draft tube to enhance mixing, a crowder plate to improve froth transport into the collection launder, and an expert control system to optimise metallurgical performances (Brewis, 1996). In the Wemco-Leeds cell, a new froth crowding system is incorporated to control the drainage and the movement of the gangue relative to the values in the froth, so as to produce a high-grade product (Degner, 1991, 1988). C. Warman flotation cells The Warman flotation cell is applied in Australia and Japan. It is characterized by an inclined-bar type rotor and a stator, as illustrated in Fig.12.23 ("Nedra", 1983). Therefore, it is also known as "bar-type" flotation cell in China.

Fig. 12.21 Wemco SmartCell flotation machine

666

SKIMMER FROTH CROWDER PLATES

AIR MANIFOLD

INTERNAL TRANSVERSE

ROD BARRIER

LAUNDER REFLUX

PULP DISCHARGE PULP FEED

V _

]

~

~

~ ,

~ L A U N D E R J DISCHANGE

IMPELLER STABILIZER

Fig. 12.22 Wemco-Leeds cell The rotor consists of some fingered or columnar bars which are fixed at a given angle to the lower part of a disc ( see Fig.12.23 (b)). When the rotor rotates, the upper part of the inclined bars has a smaller peripheral speed than the lower part, resulting in an intensive agitating and sucking effect. When air is sucked in from the central hollow shaft, mixed with pulp, and then thrown to the cell bottom at a high speed, small dispersed bubbles are formed. The resulting air-pulp mixture is dispersed into radial flows which are thrown onto all sides of the cell, and at the same time the whirling turbulent flow is eliminated by the curved flow-stabalized blades. Thereby a steadily-rising pulp flow is formed. Because this pulp flow is favourable for mineralization of the bubbles and formation of froth layers, the machine can get shallow-cell flotation, high flotation rate, and low energy consumption. In addition, since the rotor is away from the cell bottom it is not apt to submerge in sink and can be started after a long period of shut-down.

667

Fig.12.23 Warman flotation cell a. Schematic structure drawing; b. Rotor; c. Stator and flow-stabalized blades 12.2.1.1.2. "Supercharged" type mechanical flotation machines A. Denver DR and Sala AS flotation machines The DR machine is developed from the Denver Sub-A. The latter is of self-induced type with "cell to cell" tank structure, whereas the former is of supercharged type with "open flow" tank structure. Its schematic drawing is shown in Fig.12.24(a) and its characteristic drawing in Fig.12.24(b). In the DR cell, a circulation well is mounted above and through the impeller to achieve a vertical circulation of pulp above the impeller which promotes the suspension of particles (Han, 1987). The sweeping action of the homogeneous pulp-air mixture eliminates sanding and "dead zones". The Denver flotation machine dates back to about 70 years, and it is perhaps the most well known cell in mineral engineering. The recent advances with the DR flotation machines include the manufacture of larger volume cells. The machines with volume up to 43 m 3 are available (Brewis, 1991).

668 The Sala AS cell is different from the DR machine in design. The latter is designed to achieve the vertical follows to promote solid suspension, but the former aims to minimise vertical circulation. The design for the Sala AS is based on the premise that the naturally occurring stratification in the pulp is beneficial to the process. The impeller is a fiat disc with vertical radial blades on both surfaces and positioned under a stationary hood to prevent the vertical circulation, as shown in Fig.12.25. For this reason, Sala machine tanks are shallow. The machines, ranging in sizes from 1,2 to 44 m 3, are used to treat a variety of materials, including base metals, iron ore, coal and non-metallic minerals (Young, 1982; Zaman, 1989; Wills, 1997).

air

1

(a). Schematic drawing

(b). Characteristic drawing of pulp flow

1. Impeller. 2. Stationary hood. 3. sleeve. 4. Circulation well. 5. Air pipe. 6. Baffle plate. 7. Shatt. Fig. 12.24 Denver D R flotation cell

ipe

~Diffuser Rotation Impelk (cut aw

Fig. 12.25 Sala flotation m e c h a n i s m

669 Both the Denver DR and the Sala AS are now the products of Svedala Pumps & Process since the former Denver Equipment and Sala International have merged together to form it. Recently, a new design, the RCS flotation machine (Fig.12.26), has been developed by Svedala. The machine is designed with a circular tank and an impeller shaped to generate a radial flow pattern with strong return flows to both the lower and upper zones, and incorporated with the SvedalaEJ patented DV (Deep Vane) flotation mechanism which consists of an arrangement of vertical vanes with shaped lower edges and dispersion shelf. The units are available in sizes from 5 to 200 m 3 and have been installed in Europe, South America, North America, South Africa and Australia (Clifford, 1998; Arbiter, 1999).

Fig.12.26 A 130 m3 Svedala RCS flotation machine

B. Agitair flotation machines (Han, 1987; "Nedra", 1983) The Agitair flotation machine also falls into supercharged type flotation cell, as shown in Fig.12.27(a). Fig.12.27(b)-(f) show the various impellers and stabilizers used in this machine. The original Agitair impeller (Fig.12.27 (b)) is a horizontal disc with a multiplicity of fingers pointing downwards along its periphery. Air is introduced into the impeller cavity via an air inlet pipe and a

670 central hollow shaft by a low pressure blower, sheared into small bubbles by the vertical fingers, and dispersed into pulp. To meet the need of large-sized flotation cells, the Chile-X (Fig.12.27 (d)) and PIPSA (Fig.12.27 (c)) impellers were evolved. The former has fingers with a "teardrop" shape section, and the latter is essentially a Chile-X type impeller, on the top of which a centrifugal pump impeller with straight blades is mounted. This centrifugal pump impeller can produce a circulating pulp flow which helps form a large circulation of pulp above the impeller, thereby intensifying suspension of particles and dispersion of bubbles.

Fig.12.27 The Agitair flotation machine (a). Schematic structure drawing; (b). Original impeller; (c). Flow stabalizer; (d). The Chile-X impeller; (e). The PIPSA type impeller

To stabilise pulp flow, further pulverise bubbles, and form a rising aerated

671 pulp flow, a stabilizer is installed at the tank bottom. The original Agitair cell uses a square stabilizer occupying all the outer areas of the tank bottom ( Fig.12.27 (c)). But a large-sized Agitair flotation machine uses a round one ( Fig.12.27 (f)). In order to facilitate installation and removal of parts, two or four blades of the stabiliser are combined into one part. All impellers are lined with synthetic or natural rubber. The Agitair flotation machine is designed with a free-flow tank structure, each compartment of which may be up to 42.5 m 3in volume (Wills,1997). It is not able to suck pulp automatically. Therefore, external pumps are necessary for transferring intermediate flows. Like the Denver DR, the Agitair flotation machine is also well-known. It has been widely used in the world, especially in large-capacity plants, because of its simple structure, reliable operation, and convenient maintenance. C. OK flotation Cells The OK flotation machine was launched by Outokumpu Co. in the 1970s. It is characterised by the OK impeller mechanism and U-shaped tank, as shown in Fig.12.28. The impeller consists of a number of narrow vertical slots which taper downwards, the top of it being closed by a horizontal disc. As the impeller rotates, pulp is accelerated in the slots and expelled near the point of maximum diameter. Air is blown down a central hollow shaft. The pulp and air are mixed, thrown out by the impeller through the slots, and thus dispersed into an aerated pulp flow. The pulp flow is replaced by fresh pulp which enters the slots near their base where the diameter and peripheral speed are smaller, as shown in Fig.12.28 (b). Thus the impeller acts as a pump, drawing in pulp at the base of the cell and expelling it outwards. The radial blades on the stator can not only disperse air and pulp, but also prevent rotation of pulp flow in the turbulent zone. This helps to form a vertically-rising pulp flow and a stable bubble zone. The U-shaped tank ensures minimum sanding and short-circuiting (Han,1987; Nitti et al, 1986). One of the modifications of the OK machine is the introduction of froth washing and froth crowding, the so-called OK HG cell, as shown in Fig.12.29(Ulan, 1991). As the froth passes vertically upwards through the narrowing space, the squeezing effect and removal of entrained gangues can be achieved. It is claimed that the HG machine yields both high grade and high recovery. Another recent advance is the TankCell with sizes up to 160 m3. Based on the unit reactor concept that the flotation cell must be considered as a single reactor unit capable of handling specific tasks and getting excellent metallurgical performance, the TankCell includes new modified rotor-stator design, new tank geometry, and a froth- handing system (Kallioinen, 1995). The OK flotation machine has characteristics like high capacity, low energy consumption, high efficiency, and wear-resistance. It is widely applied in

672 Finland, Sweden, Canada, and the Common Wealth of Independent States. froth zone impelle]

stator stable zon( turbulent ZOrle

(b) Characteristics of pulp flow

(a) Impeller and stator

Fig. 12.28 OK flotation cell

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673 12.2.1.2 Pneumatic flotation machines

The earliest pneumatic flotation machine dates back to the patent of Norris as early as in 1907, as shown in Fig.12.30 (Jameson, 1992). But there had been no further development until the Canadian countercurrent column, which is also referred to as "conventional column", was patented in 1964 (Rubinstein, 1997; Miller, 1988; Bouton and Tremblay, 1964). However, activation of practical research work in this field began in the mid seventies. The increasing interests in pneumatic flotation machines in the past two decades have driven the generations of many new pneumatic cells and new concepts. Based on a recent novel concept, the reactor/separator concept, as shown in Fig.12.31 (Finch, 1995), a new method is tentatively used to divide pneumatic flotation machines into two types in this section" the aerationseparator type pneumatic machine, and the reactor/separator type pneumatic machine. In the former group, bubble generation, attachment of particles to bubbles, and separation of particle-laden bubbles from pulp are performed in the same vessel, while in the latter group bubbles are mixed with pulp prior to the separator. It is in the latter group that many new pneumatic flotation machines have been developed in the past two decades, as summarised in Fig.12.32.

Fig.12.30 Drawing from the patent of Norris (1907) showing a flotation column

674

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Fig. 12.31 The general concept of the reactor/separator type flotation machine Reactors/separator type Pneumatic flotation machine

r

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I

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II Top-downcomer-fedtype cell

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I

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Davcra cell Contact cell Cyclo-column CentrifloatRcell Allflot cell

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EcoCell PDM cell

Fig. 12.32 Reactor/separator type pneumatic flotation machine

12.2.1.2.1 Aeration- separator type pneumatic flotation machines A. Conventional column and its derivatives The configuration of a conventional flotation column is shown in Fig. 12.33. At the lower part of the column, there is a bubble generator, and at the upper part, there are a pulp distributor, an elution device, and a froth launder. The bubble generator's performance and arrangement has a direct influence on the flotation efficiency. There are two types of arrangement, i.e. a vertical type and a grate-like type. The latter consists of several canvas hoses or porous rubber pipes, which are horizontally arranged in a given distance at the bottom. Since canvas hoses and porous rubber pipes are not strong and liable to clog, they have been replaced by porous plastics or ceramic pipes which are vertically mounted. Industrial columns are constructed with a circular or square cross-section, 5 to 15 m in height, and up to 3.5 m in diameter (Hu, 1983; Schubert, 1988; Wills, 1997).

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-- Tail Fig.12.33 The configuration of a conventional column The pulp conditioned with the reagents is fed at a level of approximately two thirds of the column height and evenly distributed into the column by the distributor. As mineral particles sink slowly, they collide with a rising swarm of bubbles produced by the bubble generator. Floatable particles adhere to the bubbles and are transported to the froth layer. Non-floatable particles are removed from the base of the column. Entrained gangue pa~qcles are washed back into the pulp by a downward liquid flow in the column and by washing water from the elution device, hence reducing contamination of the concentrate. The main derivatives of the conventional column which belong to the aeration-separator type include the Deister Flotaire column, Microcel TM column, Packed column, and baffled column. As shown in Fig.12.34 (a) and (b), the Deister Flotaire is similar to the conventional column except for the bubble generator. The first-generation models were commercialised in 1979 to recover phosphate minerals. The air is aspirated with high-pressure water containing

676 frother in an external aspirator and introduced through two punched constriction plates at the column bottom, thus a uniform bubble stream being formed. The second-generation models were used in 1986 in sulphide, coal, and metal oxide mineral flotation. The air and water containing frother is introduced through porous-tube microdiffusers to generate fine bubbles (Jameson, 1992; Miller, 1988). Different in the bubble generator from the earlier columns, the Microcel vm column uses external bubble generators, the in-line static mixers, as shown in Fig. 12.34 (c). The bubble generators operate at low pressure and can produce strong shearing. As a result, it can generate fine bubbles and hence obtain higher recovery of fine particles, with the obvious advantages of flexibility of operation and maintenance and no use of water for bubble generation. An industrial-scale Microcel TMcolumn with 2.44 m in diameter was successfully tested in coal flotation (Luttrell, 1993). In order to reduce axial mixing, especially in full-scale columns, a pilot baffled column was designed and tested in coal flotation. The column was derived from a 20.3-cm-diameter, 9.1-m-height Deister Flotaire column in which horizontal perforated plates with openings large enough to keep them from clogging and small enough to break up vertical mixing current are mounted both above and below the feed inlet, as shown in Fig. 12.35 (Kawatra, 1995). Another distinct design is the packed column filled with a stack of corrugated plates, as shown in Fig.12.36 As the air passes upward through the packing plates, it is cut into fine bubbles, hence eliminating the need for a bubble generator or air sparger. The machine was tested on pilot scale in coal flotation and it was claimed that it can drastically reduce entrainment with the features of high throughput, low power consumption, simple control, and easy operation (Yang, 1991). B. Electro-flotation machines With ultrafine particles, extremely fine bubbles must be generated to improve attachment. Such bubbles can be generated by in situ electrolysis in a modified flotation machine. There are a great variety of electro-flotation machines. They differ mainly in the combination and arrangement of electrodes. Electro-flotation machines fall largely into 3 types, i.e. single-cell, double-cell and multi-cell. A Sengoben single-cell electro-flotation machine is shown in Fig.12.37 (Deryagin et al, 1986). In this machine, its cathode is made from stainless steel, and its anode is made from titanium plate electroplated with lead dioxide. The machine is used to purify water, with the electricity consumption below 0.2 kw.h/m3.

677 WATER FROTH CROWD~~,~ SIGHT

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679

12.2.1.2.2 Reactor/separator type pneumatic flotation machines A. Lower-or-bottom-fed type cells The earliest cell in this type is the Davcra cell (see Fig.12.38). It is simple in structure and consists mainly of a tank with one or more cyclone-type injectors. When pressured pulp enters tangentially the injector and rotates around its inner wall and compressed air from a central air pipe is introduced into the injector, two flows are formed: a rotating pulp flow and a central air flow. They are mixed at the front end of the injector, and injected into the tank via a nozzle of the injector. When the two flows are mixed, strong turbulence and shearing effect are created due to their differences in properties, speed, and trackway, hence dispersing the air into lots of small bubbles. Moreover, after pulp-air mixture is injected into the tank, the air dissolved in the pulp is released into lots of small bubbles due to a reduction in pressure. A vertical baffle is fixed in front of the injector. When air-pulp mixture from the injector runs against the baffle plate, its injection energy is dissipated. At the same time air is dispersed and the horizontally-injected flow is changed into a vertically-rising flow. These promote the particle-laden bubbles to rise. Bubble products run into a bubble collecting tank, while tailings bypass the baffle plate and run into a tailing pipe. In Australia, this machine is used mainly for lead and zinc mineral flotation (Han, 1987; Kelly et al, 1982). It has also replaced some mechanical cleaner machines at Chambishi copper mine in Zambia, with reported lower operating costs, reduced floor area and improved metallurgical performance (Wills, 1997). Other cells which fall into this type are summarised in Table 12.6. They are essentially similar except that different mixing units, or so-called reactors, are used, as shown in Fig. 12.39. B. Tangentially-side-fed type cells The Bahr cell, developed in Germany in 1974, belongs to this type, as shown in Fig.12.40 (Bahr, 1985; Cordes, 1997; Jameson, 1992). It consists of a vessel, the upper part of which is columnar and the lower part of which is conical. Around the side of the vessel there are several aerators in which air is injected through a porous wall into the transversely-moving pulp. The pulp is premixed with air in the aerators and then the resulting bubbly pulp mixture is fed tangentially into the vessel. Particle-laden bubbles rise to the froth layer where the froth flows into an outlet at the centre of the vessel, while the particles not attaching to bubbles travel downwards the tailing outlet along a spiral locus.

680

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Fig.12.38 The Davcra jet flotation machine

Table 12.6 Cell

Recent lower-or-bottom-fed reactor/separator type pneumatic cells Mixing unit (reactor)

Centrifloat R cell.

Centrifugal porous cylinder (Pulp is fed tangentially into the unit and air is introduced through its porous wall).

Contact cell.

USBM/Cominco type sparger.

Cyclo-column.

Allflot cell.

Size or scale

Application or test

Refs.

Application in coal, de-inking and de-oiling flotation.

Finch, 1995.

Pilot unit.

Test in copper/ Molybdenum flotation.

Amelunxen, 1993; Finch, 1995.

Centrifugal cylinder (Pulp and air are fed tangentially into the unit).

Laboratory. scale

Test in the reverse Yalcin,1995. flotation of magnetite ore.

Aeration reactor.

Plant scale.

Test in coal, koalin, Jungmann, 1988. quartz, and filter dust flotation.

681

Fig.12.39 Recent lower-or-bottom-fed reactor/separator type pneumatic cells Pulp is fed at 3~10 m/s and the average rotary speed of pulp on the surface is 1~2 m/s. Air dispersion and particle-bubble contact are achieved mainly by the aerators. Air-pulp mixture is jetted into the tank and enter the separation zone of bubbles immediately. As a result, lot of bubbles produced by the aerators can contact fully with mineral particles by the action of turbulent

682 flow. Therefore, better mineralized bubbles can be obtained by this machine. In Germany, the Bahr cells have been used in coal, iron ore, and magnetite flotation. The practice shows that one-stage separation by this machine can replace multiple-stage separation by mechanical flotation cells. It also can float effectively both coarse minerals above 0.2 mm and fine minerals below 0.01mm. Moreover, this machine is characterized by good selectivity, high flotation rate, low energy consumption, and insensitivity to the fluctuation in feed.

•Concentrate Tailing~

Fig. 12.40 The Bahr cell

C. Top-downcomer-fed type cells The recent cells in this type, which have been applied in industry, are the Jameson cell (Jameson, 1988; Harbort, 1994) and the EKOFLOT cell( Sanchez et al., 1997), as illustrated in Fig.12.41. They are very similar in structure. Both cells mainly consist of a short column into which there is a vertical downcomer (maybe several downcomers in a large Jameson cell) with an aerator (mixing unit) at its top. In the Jameson cell, the pulp is fed to the top of the downcomer as a simple liquid jet, and unpressurized air is entrained into the pulp and broken up into fine bubbles. The bubble-pulp mixture flows downwards via the downcomer to discharge into the lower part of the column. The bubbles disengage and rise to the top of the column to overflow into a concentrate launder, while the tails are discharged from the bottom of the column (Jameson, 1992; Wills, 1997). The Jameson cell was developed in Australia in mid-1980s. It has been used in a number of cleaning operation within Mount Isa Mines Ltd and other mines in Australia (Kennedy, 1990; Clayton et al, 1991; Harbort et al, 1994). There were more than 120 cells installed worldwide processing coal, base metals, and industrial minerals ( Carter, 1997).

683 The EKOFLOT cell works a similar way to the Jameson cell except that the EKOFLOT cell uses a different aerator into which compressed air is fed (Cordes, 1997). In addition, a moveable cone is mounted at the top of the column to adjust the volume of the froth which overflows into the froth launder. The EKOFLOT cell has been applied in copper rougher, scavenger or cleaner flotation at Minera Michilla S.A. in Chile, with reported high selectivity, low energy consumption, and reduced floor area (Sanchez, 1997; Cordes, 1997).

Fig.12.41 Top-downcomer-fedtype pneumatic cells

12.2.2. COMBINATION OF INTERFACE SEPARATION PR OCESSES.

SEPARATION AND

OTHER

Apart from the above flotation equipment, there are some separation devices, in which interfacial separation and other separation processes are combined, such as floatation jig, particle-floating table, and air-sparged hydrocyclone. Fig.12.42 depicts an air-sparged hydrocyclone. The device is a gravityflotation separator, into which flotation and hydrocyclone are integrated. In this device, the side wall is made of porous media. Pulp pretreated by flotation reagent is fed tangentially into the hydrocyclone at a high pressure. Thus eddies nearby the inner wall are formed. Hydrophilic mineral particles and most of water are discharged with eddy flow as an underflow. Air is pressed into the

684 cyclone through the porous wall and is turned into bubbles. A stable bubble column at the centre of the cyclone is discharged with hydrophobic mineral particles as an overflow. The air-sparged hydrocyclone is a new type of separating machine which can increase flotation rate of fine minerals. In conventional flotation separation, the flotation rate of fine materials is limited, because of low collision probability, insufficient inertia to penetrate bobbles, and unstable bubbleparticle aggregates. However, in the air-sparged hydrocyclone, because a controllable strong centrifugal force field produced by eddy flow increases the inertia of fine particles, they can be brought into direct contact with lots of micro bubbles on the porous wall. Therefore. their collision efficiency is quite high. Moreover, the flotation rate is also high due to the short retention time of mineralized bubbles in the cyclone. Applications of this device in separation of gold, copper, oilshale, and coal have demonstrated its good prospects (Miller et al, 1985, 1988; Yalamachili, 1995).

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685

REFERENCES Amelunxen, R.L. (1993). The contact cell-A future generation of flotation machines. E&Mj, April, 36 Arbiter, N. (1999). Development and Scale-up of Large Flotation Cells. Advances In Flotation Technology, eds. B.K.Parekh and J.D.Miller, SEM Inc., Littleton, 345-352 Bahr, A.; Imhoff, R.; Ludke, H. (1985). Application and Sizing of a New Pneumatic Flotation Cell. Proceedings of XV International Mineral Processing Congress, Cannes, Edition GEDIM, Vol.2, 314-325 Beixer, P. (1964). Emulsification Theory and Practice, Science Press, China, 203-220 Boutin, P., and Tremblay, R.J. (1964). Method and apparatus for the separation and recovery of ores, Canadian Patent, No.694547 Brewis, T. (1996). Flotation cells. Mining Magazine, July, 18 Brewis, T. (1991). Flotation cells. Mining magazine, June, 383 Carter, R.A., (1997). Australia research yields innovative equipment. Coal Age, May, 52 Clayton, R.; Jameson, G.J. and Manlapig, E.V. (1991). The Development and Application of the Jameson cell. Minerals Engineering, Vol.4, Nos.7-11,925-933 Clifford, D. (1998). Flotation advances. Mining Magazine, Vol. 179, No. 5, 235-236, 238, 240-241,243-244 Cordes, H. (1997). Development of pneumatic flotation cells to their present day status. Aufbereitungs Technik38, Nr.2, 69 Dai, Zhongfu (1986). Master Thesis, Wuhan Institute of Iron and Steel, China Degner, V.R. (1988). Mechanical flotation design. In: Proceedings of industrial practice of fine coal processing. Hidden Valley, Somerset, PA, 135 Degner, V.R. (1988). Wemco/Leeds flotation column development. In: Column'88, ed. V. Sastry, SME, Inc., Littletown, CO., US., 267 Degner, V.R. (1991). Leeds column performance evaluation. Minerals Engineering, Vol.4, Nos.7-11,935 Deryagin B.V., Dukhin S.S., Pulev I.I. (1986). Microflotation on Purification of waste water from Mineral Processing, "Chimia", Moscow Edwards, M.F. (1985) Mixing in the Process Industries, Harnby, N.,Edwards, M.F. and Nierow, A.W., eds., Chapter 7, 113-130, Butterworths, London Finch, J. A. (1995). Column flotation: a selected review-part IV: novel flotation devices. Minerals Engineering, Vol. 8, No. 6, 587 Glembotskii V.A., Klassen V.I. (1981). Flotation Methods, "Nedra", Moscow, 204-223

686 Han, Deyou (1987). Technology for Coal Dressing, China, No.2, 28-31 Han, Shoulin (1987). New Flotation Equipment and Its Application, Scientific Technology Network for Mineral Processing, China Harbort, G.J., Jackson, B.R., and Manlapig, E.V. (1994). Recent advances in Jameson flotation cell technology. Minerals Engineering, Vol.7, Nos.2/3, 319 Hu, Weibo (1983). Flotation, Metallurgical Industry Press, China, 169-206 Jameson, G.J. (1988). A new concept in flotation column design. In: Column'88, ed. V. Sastry, SME, Inc., Littleton, CO., US., 281 Jameson, G.J. (1992). Flotation cell development. In: AuslMM Annual Conference Series, AuslMM, Parkville, Australia, 25 Jungmann, A., and Reilard, U.A. (1988). Investigations into pneumatic flotation of various raw and waste materials using the Allflot system. Aufbereitungs Technik, Nr.8,470 Kallioinen, J., Heiskanen, K., and Garrett, C. (1995). Large flotation cell tests successful in Chile. Mining Engineering, October, 913 Kawatra, S.K., and Eisele, T.C. (1995). Baffled-column flotation of a coal plant fine-waste stream. Minerals and Metallurgical Precessing, August, 138 Kelly, E.G., and Spottiswood, D.J. (1982). Introduction to Mineral Processing, New York, 301-306 Kennedy, A. (1990). The Jameson Flotation Cell. Mining Magazine, Vol. 163, No. 4, 281-285 Klassen V.I. (1963). Coal Flotation, "Nauch. Techn. Izdat.", Mosco, 193-195 Luttrell, G H, Mankosa, M J, and Yoon, R-H (1993). Design and scale-up criteria for column flotation. XVIII International Mineral Processing Congress, Sydney, 785 Miller, JD.; Upadrashta, KR.; Kinneberg, DJ.; Gopalakrishnan, S. (1985). Fluid-Flow Phenomena in the Air-Sparged Hydrocyclone. Proceedings of XV International Mineral Processing Congress, Cannes, Edition GEDIM, Vol.2, 87-99 Miller, JD., Ye, Y., Pacquet, E., Baker, M.W., and Gopalakrishnan, S. (1988). Design and operating variables in flotation separations with the air-sparged hydrocyclone. XVI International Mineral Processing Congress, ed. E. Forssberg, Elsevier Science Publishers B.V., Amsterdam, 499 Miller, K.J. (1988). Novel flotation technology-A survey of equipment and processes. Industrial Practice of Fine Coal Processing, In: Proceedings of industrial practice of fine coal processing. Hidden Valley, Somerset, PA, 347 Mineral Processing Division, Tangshan College of Engineering and Technology (1987). Metal and Mine, China, No. 11, 42-44 "Nedra". (1983). Handbook of Mineral Dressing, Chapter Three: Main Process, Moscow "Nedra". (1983). Handbook of Mineral Dressing, Chapter Six: Special and Auxiliary Process, Moscow

687 Nitti, T., and Tarvainen, M. (1986). Proceedings of XIV International Mineral Processing Congress, Vol.9-10, 151-158 Oshima, H. Chemical Mill, Vol.29, No9, 42-45 Rubinstein, J. (1997). Column flotation: Theory and practice. Proceedings of the XX International Mineral Processing Congress, eds. Heinz Hoberg and Harro von Blottnitz, Clausthal-Zellerfeld, Germany: GMDB Gesellschaft fur Bergbau, Metallurgie, Rohstoff- und Umwelttechnik, Vol.3, 185 Saitou, K. (1987). Mineral processing Machinery, No4, 66-75 Sanchez, S.P., Rojos, F.T., Fuemes, G,B., Latorre, J.G., Conejeros, V.T., and Carcamo, H.G. (1997). EKOF pneumatic flotation technology: the alternative for rougher, scavenger or cleaner flotation of metallic ores. Proceedings of the XX International Mineral Processing Congress, eds. Heinz Hoberg and Harro yon Blottnitz, Clausthal-Zellerfeld, Germany: GMDB Gesellschaft fur Bergbau, Metallurgie, Rohstoff- und Umwelttechnik, Vol.3,255 Schubert, H. (1988). Counter-flow flotation cells (flotaion columns)-Present state and current trends. Aufbereitungs Technik, Nr.6, 307 Shanghai Research Institute of Chemical Technology, Tests of emulsification by static mixer, China Stein, H.N., (1996). The Preparation of Dispersions in Liquids, Marcel Dekker, Inc., New York Suppliers news, (1997). SmartCell shows it's a smart buy. E&Mj, Feb., 57 Ulan, W.W., Green, D., and Koslck, G.A. (1991). In-plant testing of the Outokumpu High Grade flotation cell. In: Column'91, ed. G.E.Agar, CIMMP, Canada, 689 Wills, B.A. (1997). Mineral Processing Technology, sixth edition. Oxford: ButterworthHeinemann, 294 Xia, Tianxian (1985). Zhejiang Chemical Technology, China, No.2, 15-21 Yalamanchili, M.R., and Miller, J.D. (1995). Removal of insoluble slimes from potash ore by air-sparged hydrocyclone flotation. Minerals Engineering, Vol.8, No.l/2, 169 Yalcin, T. (1995). The effect of some design and operating parameters in the cyclo-column cell. Minerals Engineering, Vol.8, No.3, 311 Yang, D.C. (1991). Technical advantages of Packed flotation packed flotation column. In: Column'91, ed. G.E.Agar, CIMMP, Canada, 631 Ye, Chubao (1988). Chemical Engineering, China, No.l, 51-57. Young, P. (1982). Flotation machines. Mining Magazine, January, 35

688 Zaman, S., and Hazen, B. (1989). The evolution of the conventional flotation cell design. In: Proceedings of Advances in Coal and Mineral Processing Using Flotation, Society of Mining Engineers of AIME, Littleton, CO., 347 Zhou, Yousheng, and Dong, Yiren (1985). Chemical Mechanic, China, Vol.12, No.3, 28-36.