Presentation on theme: "FLOTATION Flotation process (sometimes called flotation separation) is a method of separation widely used in the wastewater treatment and mineral processing."— Presentation transcript:
1FLOTATIONFlotation process (sometimes called flotation separation) is a method of separation widely used in the wastewater treatment and mineral processing industries.
2PRINCIPLES OF FLOTATION Mechanism of froth flotation are:Attachment of a specific mineral particle to air bubblesBeing carried by the water in the flothCaught b/w particles in the froth
3In flotation concentration mineral is transferred to the froth leaving the gangue in the pulp. This is direct flotation.In reverse flotation, gangue is separated into the froth fraction. Air bubbles can only stick to the mineral particles if they can displace water from the mineral surface which means that the mineral has to be hydrophobic. Air bubbles can continue to support the mineral particles at the surface only if they can form a stable froth which is achieved by using floatation reagents.
4Various flotation processes include the following: Dissolved air flotationInduced gas flotationFroth flotation, typical in the mineral processing industry
5DISSOLVED AIR FLOTATION Dissolved air flotation (DAF) is a water treatment process that clarifies wastewaters (or other waters) by the removal of suspended matter such as oil or solids. The removal is achieved by dissolving air in the water or wastewater under pressure and then releasing the air at atmospheric pressure in a flotation tank or basin. The released air forms tiny bubbles which adhere to the suspended matter causing the suspended matter to float to the surface of the water where it may then be removed by a skimming device.[Dissolved air flotation is very widely used in treating the industrial wastewater effluents from oil refineries, petrochemical and chemical plants, natural gas processing plants, paper mills, general water treatment and similar industrial facilities. A very similar process known as induced gas flotation is also used for wastewater treatment. Froth flotation is commonly used in the processing of mineral ores.In the oil industry, dissolved gas flotation (DGF) units do not use air as the flotation medium due to the explosion risk. Natural gas is used instead to create the bubbles.
7The feed water to the DAF float tank is often (but not always) dosed with a coagulant (such as ferric chloride or aluminum sulfate) to flocculate the suspended matter.A portion of the clarified effluent water leaving the DAF tank is pumped into a small pressure vessel (called the air drum) into which compressed air is also introduced. This results in saturating the pressurized effluent water with air. The air-saturated water stream is recycled to the front of the float tank and flows through a pressure reduction valve just as it enters the front of the float tank, which results in the air being released in the form of tiny bubbles. The bubbles adhere to the suspended matter, causing the suspended mater to float to the surface and form a froth layer which is then removed by a skimmer. The froth-free water exits the float tank as the clarified effluent from the DAF unit.Some DAF unit designs utilize parallel plate packing material, lamellas, to provide more separation surface and therefore to enhance the separation efficiency of the unit.
8INDUCED GAS FLOTATIONInduced Gas Flotation (IGF) is a water treatment process that clarifies wastewaters (or other waters) by the removal of suspended matter such as oil or solids. The removal is achieved by injecting air bubbles into the water or wastewater in a flotation tank or basin. The small bubbles adhere to the suspended matter causing the suspended matter to float to the surface of the water where it may then be removed by a skimming device.Induced Gas Flotation is very widely used in treating the industrial wastewater effluents from oil refineries, petrochemical and chemical plants, natural gas processing plants and similar industrial facilities. A very similar process known as dissolved air flotation is also used for waste water treatment. Froth flotation is commonly used in the processing of mineral ores.IGF Units in the oil industry do not use air as the flotation medium due to the explosion risk. These IGF Units use natural gas to create the bubbles.
9The feed water is to the IGF float tank is often (but not always) dosed with a coagulant (such as ferric chloride or aluminum sulfate) to flocculate the suspended matter.The bubbles may be generated by an impeller, eductors or a sparger. The bubbles adhere to the suspended matter, causing the suspended mater to float to the surface and form a froth layer which is then removed by a skimmer. The froth-free water exits the float tank as the clarified effluent from the IGF unit.Some IGF unit designs utilize parallel plate packing material to provide more separation surface and therefore to enhance the separation efficiency of the unit.
10FROTH FLOTATIONFroth flotation is a process for selectively separating hydrophobic materials from hydrophilic. This is used in several processing industries. Historically this was first used in the mining industry.Eg oxides-hematite,cassiterite;oxidised- malachite,cerussite;non metallic- fluorite,phosphate,fine coal;sulphides- copper,zinc,lead
13WASTE WATER TREATMENTThe flotation process is also widely used in industrial waste water treatment plants, where it removes fats, oil, grease and suspended solids from waste water. These units are called Dissolved air flotation (DAF) units. In particular, dissolved air flotation units are used in removing oil from the wastewater effluents of oil refineries, petrochemical and chemical plants, natural gas processing plants and similar industrial facilities.
14PAPER RECYCLINGFroth flotation is one of the processes used to recover recycled paper. In the paper industry this step is called deinking or just flotation. The target is to release and remove the hydrophobic contaminants from the recycled paper. The contaminants are mostly printing ink and stickies. Normally the setup is a two stage system with 3,4 or 5 flotation cells in series
15Chemicals for deinking of recycled paper pH control: sodium silicate and sodium hydroxideCalcium ion source: hard water, lime or calcium chlorideCollector: fatty acid, fatty acid emulsion, fatty acid soap and/or organo-modified siloxane
16PRINCIPLE OF OPERATION Froth flotation commences by comminution (that is, crushing and grinding), which is used to increase the surface area of the ore for subsequent processing and break the rocks into the desired mineral and gangue in a process known as liberation, which then has to be separated from the desired mineral. The ore is ground into a fine powder and mixed with water to form a slurry. The desired mineral is rendered hydrophobic by the addition of a surfactant or collector chemical. The particular chemical depends on which mineral is being refined. As an example, pine oil is used to extract copper (see copper extraction). This slurry (more properly called the pulp) of hydrophobic mineral-bearing ore and hydrophilic gangue is then introduced to a water bath which is aerated, creating bubbles. The hydrophobic grains of mineral- bearing ore escape the water by attaching to the air bubbles, which rise to the surface, forming a foam or a scum (more properly called a froth). The froth is removed and the concentrated mineral is further refined.
17SCIENCE OF FLOTATIONTo be effective on a given ore slurry, the surfactants are chosen based upon their selective wetting of the types of particles to be separated. A good surfactant candidate will completely wet one of the types of particles, while partially wetting the other type, which allows bubbles to attach to them and lift them into a froth. The wetting activity of a surfactant on a particle can be quantified by measuring the contact angles that the liquid/bubble interface makes with it. For complete wetting the contact angle is zero.Another consideration, especially important for heavy particles, is to balance the weight of the particle with the surfactant adhesion and buoyant forces of the bubbles that would lift it.For typical values of metal densities and surface tensions, if the bubbles are larger than the ore particles, and the particles are equal to or less than 1 mm radius, then particles will rise into the froth layer if:where is the radius of the particles, is the average surface tension between the three pairs of phases (particle, flotation solution, air), is the mass density of the particles, and is the acceleration of gravity (9.81 m/s2).For particles larger than the bubbles, they too can rise into the froth, each buoyed by a swarm of bubbles, under similar conditions as those expressed in the inequality.
18FLOTATION EQUIPMENTDiagram of froth flotation cell. Numbered triangles show direction of stream flow. A mixture of ore and water called pulp  enters the cell from a conditioner, and flows to the bottom of the cell. Air  or nitrogen is passed down a vertical impeller where shearing forces break the air stream into small bubbles. The mineral concentrate froth is collected from the top of the cell , while the pulp  flows to another cell.Flotation can be performed in rectangular or cylindrical mechanically agitated cells or tanks, flotation columns, Jameson cells or deinking flotation machines.Mechanical cells use a large mixer and diffuser mechanism at the bottom of the mixing tank to introduce air and provide mixing action. Flotation columns use air spargers to introduce air at the bottom of a tall column while introducing slurry above. The countercurrent motion of the slurry flowing down and the air flowing up provides mixing action. Mechanical cells generally have a higher throughput rate, but produce material that is of lower quality, while flotation columns generally have a low throughput rate but produce higher quality material.The Jameson cell uses neither impellers nor spargers, instead combining the slurry with air in a downcomer where high shear creates the turbulent conditions required for bubble particle contacting.s
20MECHANICS OF FLOTATION The following steps are followed:Grinding to liberate the mineral particlesReagent conditioning to achieve hydrophobic surface charges on the desired particlesCollection and upward transport by bubbles in an intimate contact with air or nitrogenFormation of a stable froth on the surface of the flotation cellSeparation of the mineral laden froth from the bath (flotation cell)
211) pneumatic machines either use air entrained by turbulent pulp addition(cascade cells), or more commonly air either blown in or induced, in which case air must be dispersed either by baffles or some form of permeable base within the cell. It gives low grade concentration &little operating trouble.The davcra cell is used for roughing or cleaning operations.Most resent is floatation column.
22Mechanical floatation characterized by a mechanically driven impeller which agitates the slurry and disperses the incoming air into small bubbles.Criterions for assessing cell performance are:Metallurgical performance i.e. product recovery & grade.Capacity in tonnes treated per unit volume.Power consumption/tonne.economicali.e. initial, operation & maintenance cost
24SIMPLE FLOTATION CIRCUIT FOR MINERAL CONCENTRATION Numbered triangles show direction of stream flow, Various flotation reagents are added to a mixture of ore and water (called pulp) in a conditioning tank. The flow rate and tank size are designed to give the minerals enough time to be activated. The conditioner pulp  is fed to a bank of rougher cells which remove most of the desired minerals as a concentrate. The rougher pulp  passes to a bank of scavenger cells where additional reagents may be added. The scavenger cell froth  is usually returned to the rougher cells for additional treatment, but in some cases may be sent to special cleaner cells. The scavenger pulp is usually barren enough to be discarded as tails. More complex flotation circuits have several sets of cleaner and re-cleaner cells, and intermediate re-grinding of pulp or concentrate.
25FLOTATION REAGENTSA composition and process are provided for the recovery of the values of zinc, molybdenum, copper, lead, iron (pyrite), and iron-containing small amounts of gold or uranium, or both, from ores comprising these mineral sulfides. The aqueous composition is the impure form of an alkali metal alkyl trithiocarbonate compound. The process comprises employing said aqueous composition as a collection agent for the above minerals in an ore recovery process.A process for the separation of zinc values from lead values from an ore comprising both is provided by employing an alkali metal alkyl trithiocarbonate compound as a collection agent for zinc.In addition, both a composition and process are provided for the recovery of the values of iron, copper, and lead from ores comprising these values. The composition consists essentially of a dispersant and an impure form of an alkali metal alkyl trithiocarbonate compound. The process comprises employing this composition as a collection agent for the above minerals in an ore recovery process.
26CHEMICALS OF FLOTATION CollectorsCollectors either chemically bond (chemisorption) on a hydrophobic mineral surface, or adsorb onto the surface in the case of, for example, coal flotation through physisorption. Collectors increase the natural hydrophobicity of the surface, increasing the separability of the hydrophobic and hydrophilic particles.
28FrothersFrothers produces stable bubbles for hydrophobic particles to attach to.work in liquid phase only and not to mineral surface.It should have low collecting power.Reduce surface tention.Pine oilAlcohols (MIBC)PolyglycolsPolyoxyparafins|Cresylic Acid (Xylenol)
29ModifiersModifiers as activators, depressants or pH modifiers. Alters selectivity of the collectors.It intensifies or reduces their water repellant effect on the mineral surface.Activator-soluble salts which ionizes in solutionEg activation of sphalerite by cu in solutionDepressant-are used to increase the selectivity of floatation by rendering certain minerals hydrophilic thus preventing their floatation.Eg slime coatingCationic modifiers:Ba2+, Ca2+, Cu+, Pb2+, Zn2+, Ag+Anionic modifiers:SiO32-, PO43-, CN-, CO32-, S2-Organic modifers:Dextrin, starch, glue, CMC
30pH modifier floatation is carried out at alkali pH because most collector are stable at higher pH & corrosion of cells, pipework is minimized.pH modifiers such as:Lime CaOSoda ash Na2CO3Caustic soda NaOHAcid H2SO4, HCl
31Specific ore applications Sulfide oresCopper (see copper extraction) Copper-Molybdenum Lead-Zinc Lead-Zinc-Iron Copper-Lead-Zinc-Iron Gold-Silver Oxide Copper and Lead Nickel Nickel-Copper Nonsulfide oresFluorite Tungsten Lithium Tantalum Tin Coal
32Ore Concentration by Froth Flotation Remember that only 0.67% of the ore is copper. The copper minerals and waste rock are separated at the mill using froth flotation. The copper ore slurry from the grinding mills is mixed with milk of lime (simply water and ground-up limestone) to give a basic pH, pine oil (yes, it comes from trees -- a by-product of paper mills) to make bubbles, an alcohol to strengthen the bubbles, and a collector chemical called potassium amyl xanthate (or the potassium salt of an alkyl dithiocarbonate).The xanthates are added to the slurry in relatively small quantities. Xanthate is a long hydrocarbon (5 carbons) chain molecule. One end of the chain (the ionic dithiocarbonate) is polar and sticks to sulfide minerals while the other end is nonpolar, containing the hydrocarbon chain is hydrophobic -- it hates being in the water and is attracted to the nonpolar hydrocarbon pine oil molecules.
33 Raising the pH causes the polar end to ionize more and to preferentially stick to chalcopyrite (CuFeS2) and leave the pyrite (FeS2) alone. Air is blown into the tanks and agitated like a giant blender, producing a foamy froth. The chalcopyrite grains become coated with xanthate molecules with their hydrophobic ends waving around trying desperately to get out of the water. They attach themselves to the oily air bubbles which become coated with chalcopyrite grains as they rise to the surface and flow over the edge of the tank. In this manner through a series of steps the copper ore is concentrated to an eventual value of over 28% copper. Waste rock particles do not adhere to the bubbles and drop to the bottom of the tank. The waste material that comes out of the bottom of the tanks at the tail end of this process is called "tailings." It is nothing more than ground-up rock with the copper minerals removed.
34MIDDLINGS THICKENERThe bubbles that flow over the edge of the first set of flotation tanks (inside the mill building) end up in this thickener. By then the bubbles have broken and the slurry is poured into the center of this round tank. The solid material settles to the gently sloping bottom and is pushed toward the center by a systems of rakes that slowly revolve around the tank.The thickened slurry is pumped back into the mill for further processing. The clarified water flows under the small dam, that you can see just inside the perimeter of this tank, flows over the side, and is pumped back to the mill for reuse.That stuff floating on top is "almost money" - just chalcopyrite that hasn't sunk in the tan yet. A water spray on the opposite side of that radial walkway helps sink it.
35AIR BUBBLEText edited by Rob Vugteveen, Director, Asarco Mineral Discovery CenterThe graphic down shows an air bubble surrounded by grains of chalcopyrite that has been coated with xanthate. The pine oil acts as a frother only, providing the air bubbles that the xanthate sticks to.
37HISTORY OF FLOTATION DEVELOPMENT The earliest patent relating to the mineral flotation process is that of Haynes in 1860. his recognition of the differences in wettability of various minerals by water and oil formed the basis for a number of “oil” flotation processes. During the next fifty years, there principal stages of flotation development occurred:Bulk oil flotation used the fact minerals of metallic luster are preferentially wetted by oil the presence of water – consequently passing into the interface between the oil and water – while the water – wetted gangue (worthless rock) drops out. This process requires large amounts of oil – usually one part for each part of are.Skin flotation used the fact that when finely ground dry ore was gently brought into contact with still water, the metallic particles tended to float more than did the gangue. This process was developed between However, both skin and bulk oil flotation were made obsolete by the froth flotation process.
38HISTORYWilliam Haynes in 1869 patented a process for separating sulfide and gangue minerals using oil and called it bulk-oil flotation.The first successful commercial flotation process for mineral sulphides was invented by Frank Elmore who worked on the development with his brother, Stanley. The Glasdir copper mine at Llanellyd, near Dolgellau, in North Wales was bought in 1896 by the Elmore brothers in conjunction with their father, William Elmore. In 1897, the Elmore brothers installed the world's first industrial size commercial flotation process for mineral beneficiation at the Glasdir copper mine. The process was not froth flotation but used oil to agglomerate pulverised sulphides and buoy them to the surface, and was patented in 1898 with a description of the process published in 1903 in the Engineering and Mining Journal. By this time they had recognized the importance of air bubbles in assisting the oil to carry away the mineral particles. The Elmores had formed a company known as the Ore Concentration Syndicate Ltd to promote the commercial use of the process worldwide. However developments elsewhere, particularly in Australia by Minerals Separation Ltd, led to decades of hard fought legal battles and litigations which, ultimately, were lost as the process was superseded by more advanced techniques.The modern froth flotation process was independently invented the early 1900s in Australia by C.V Potter and around the same time by G.D Delprat. Initially, naturally occurring chemicals such as fatty acids and oils were used as flotation reagents in a large quantity to increase the hydrophobicity of the valuable minerals. Since then, the process has been adapted and applied to a wide variety of materials to be separated, and additional collector agents, including surfactants and synthetic compounds have been adopted for various applications.In the 1960s the froth flotation technique was adapted for deinking recycled paper.
39REFERENCES^ a b Beychok, Milton R. (1967). Aqueous Wastes from Petroleum and Petrochemical Plants (1st ed.). John Wiley & Sons. LCCN ^ Lawrence K. Wang, Yung-Tse Hung, Howard H. Lo and Constantine Yapijakis (2004). Handbook of Industrial and Hazardous Wastes Treatment (2nd ed.). CRC Press. ISBN ^ Kiuru, H.; Vahala, R., eds (2000). "Dissolved air flotation in water and waste water treatment". International conference on DAF in water and waste water treatment No. 4, Helsinki, Finland. IWA Publishing, London. ISBN Flotation Concentration Asarco Mining Operations in Arizona,Mission Mine, Tucson,Text edited by Rob Vugteveen, Director, Asarco Mineral Discovery Center