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metallurgy notes,mineral dressing,mod 4,Lecture 10
 

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    metallurgy notes,mineral dressing,mod 4,Lecture 10 metallurgy notes,mineral dressing,mod 4,Lecture 10 Presentation Transcript

    • MINERAL DRESSING METALLURGY , SEM 3 MODULE 4 LECTURE 10 Ref: Chapter 15 , “ Mineral processing”, S.K.JAIN, CBS PUBLISHERS & DISTRIBUTORS P Ltd, N Delhi, 2012. Chapters 20, “Principles of Mineral Dressing” , A. M. Gaudin, Tata Mc Graw Hill, 1993 . 1
    • SOLID FLUID SEPARATION 2
    • SOLID FLUID SEPARATION DECANTATION. Separation of particulates from a liquid by allowing the solids to settle to the bottom of the mixture and pouring off the particle-free part of the liquid. It is similar to ‘ thickening ‘ in principle. The pulp is allowed to settle in a tank. The clear liquid at the top is decanted by siphon / pumping. 3
    • SOLID FLUID SEPARATION COUNTER CURRENT DECANTATION ( C C D) . The feed moves from the first separator to the last and the water in the opposite direction. Feed to each stage consists of Under flow ( U/F ) from preceding stage plus Over flow ( O/F ) from following stage. O/F and U/F move counter-currently Higher recoveries and greater washing efficiency achieved. 4
    • SOLID FLUID SEPARATION COUNTER CURRENT DECANTATION ( C C D) 5
    • SOLID FLUID SEPARATION FILTRATIONProcess of separation of finely divided solid particles from a fluid by driving the pulp through a membrane / septum . The membrane is porous to permit the passage of fluid . It retains the solids. The filter cloth should give minimum resistance to the flow of the fluid. It should be strong enough to support the solid particles – EFFECTIVE SOLID BED. The pulp is presented at one side of the filter at a HIGH PRESSURE than on the other side of the filter bed. The pressure difference may be due to gravity, applied pressure, 6 vacuum, effect of centrifugal force.
    • SOLID FLUID SEPARATION MECHANISM OF FILTRATIONThe simplest type of filter Thickness of the filter Has a tube of small bore ( pore ) . The fluid is sucked through it. Some fine particles may go through the pore. The solid particles stick at the entrance. It allows only clear liquid to flow through the bore. The diameter of the coarsest solid particle is more than a MINIMUM SIZE. The MINIMUM SIZE is 1/3 of the pore opening for a coarse material. In the beginning , larger particles bridge pore. Now the smaller particles lodge inside the interstices. After a short period the FILTRATE will NOT HAVE any fine particles. Direction of flow Captured particles 7
    • RATE OF FILTRATION- SOLID FLUID SEPARATION Rate of filtration = driving force/resistance The factors affecting1. The filtering area – Rate of filtration increases as the filtering area increases. 2. Difference in pressure between the two sides of the filter- Larger this difference, greater is the rate of filtration. 3. Average cross section of the pores within the filter cake – The filter cake is supposed to be made of capillaries. Flow through each capillary is proportional to ( its radius )4 . 4. Number of pores / unit area of the filter cloth- Rate of filtration increases as this factor increases. It depends on the pulp characteristics. 5. Thickness of the filter cake – As it increases, filtration rate decreases. 6. Pulp temperature – Higher the temperature, more is the filtration rate. 7. Degree of flocculation ( dispersed material takes more time to get filtered ) , size range of particles etc. 8
    • SOLID FLUID SEPARATION RATE OF FILTRATIONHENRY DARCY’S LAW dV / dt = K ( A P ) / ( u l ) where V = volume of filtrate, t = time of filtration , K = constant for the filter medium and filter cake , A = area of filter medium , P = pressure drop across the filter medium and filter cake , u = viscosity of the filtrate and l = thickness of cake. 9
    • SOLID FLUID SEPARATION FILTERING EQUIPMENTS ( FILTERS ) Classified according to 1. whether pressure is applied on the pulp to push the liquid through the filter bed or 2. whether suction is applied to pull it through the bed. The filters can be GRAVITY FILTERS, PRESSURE FILTERS, SUCTION ( VACUUM ) FILTERS, CENTRIFUGAL FILTERS. 10
    • SOLID FLUID SEPARATION FILTERING EQUIPMENTS ( FILTERS ) 1.GRAVITY FILTERS ( HARDINGE SUPER THICKENER ) – The membrane ( septum ) acts as a support for the bed of the material. It is a FILTER THICKENER – combines filtration with thickening. PRESSURE FILTRATION on a thinner sand bed is done. Over flow Tank The fine material clogs the interstices upto a certain extent. It gives two liquors – overflowing liquor and the filtrate. Recommended when: the mixture is hot (above room temperature), the liquid is saturated with one or more reagents, the solvent is very volatile (chloroform, alcohols, ethers). Sand bed Filtrate Underflow ‘E’ rotates as the rake in a thickener. 11
    • SOLID FLUID SEPARATION 2.PRESSURE FILTERS ( PLATE AND FRAME FILTERS ) They are vessels with porous filters. The filtering membrane is stretched over a frame. A number of such frames are arranged in a press. The feed is pumped into the vessel through channels. Pressure is exerted on the filters by air / manually. When the pressure reaches a predetermined value, feed stops. The solid cake from each frame is now washed with water under pressure. The cakes are removed. Mostly used in Hydrometallurgical processes. 12
    • SOLID FLUID SEPARATION PLATE AND FRAME PRESS 13
    • SOLID FLUID SEPARATION - PLATE AND FRAME FILTERS 14
    • SOLID FLUID SEPARATION - PLATE AND FRAME FILTERS 15
    • SOLID FLUID SEPARATION 3. VACUUM FILTERS ( SUCTION FILTERS ) – feed Suction or vacuum is applied at the filtrate side. Can be used for intermittent or continuous operation. GENTER THICKENER - Intermittent operation. Many cylindrical filtering elements ( canvas bags ) dip in the measured slurry in a tank. Suction is applied through them. The cake is formed on the outside of the elements. They are removed by short counter flow. It is more of a filter than a thickener. 16
    • SOLID FLUID SEPARATION- GENTER 17
    • SOLID FLUID SEPARATION VACUUM FILTERING 18
    • SOLID FLUID SEPARATION VACUUM FILTERS ( SUCTION FILTERS ) DRUM FILTERS – Continuous operation. A rotating drum has FILTER PLATES on its circumference. They are covered with cloth . The drum rotates at a very slow speed. The drum is partially immersed in the pulp to be filtered. Suction is applied to the filters from inside using vacuum pumps. The cake sticks to the surface of the filter cloth on the drum. It is removed continuously. Tank drum with compartments Vacuum sucking filter slurry 19
    • SOLID FLUID SEPARATION DRUM FILTERS 20
    • SOLID FLUID SEPARATION DRUM FILTERS 21
    • SOLID FLUID SEPARATION VACUUM FILTERS ( SUCTION FILTERS ) DISC FILTERS – Continuous operation. A large number of filter cloth covered discs replace the drum in the vacuum filter. It easy to replace the filter cloth. More easy to use for more than one product at a time. 22
    • SOLID FLUID SEPARATION DISC FILTERS 23
    • SOLID FLUID SEPARATION DISC FILTERS 24
    • SOLID FLUID SEPARATION PRESSURE AND SUCTION FILTERS: Advantages.  higher fluid capacity per square foot of filtering surface,  better control of cake formation,  possibility of better washing of cake. Disadvantage.  A great disadvantage is that they are intermittent (stopping and starting at regular intervals) instead of continuous. 25
    • SOLID FLUID SEPARATION CENTRIFUGAL operation. FILTERS – Intermittent Used to dewater granulated coal, metal powders etc. It has a revolving ( at a very high speed ) filtering basket of cylindrical / cylindro-conical shape . It is lined with a filtering surface. The suspension is pressed to the filtering basket due to centrifugal forces. The liquid passes through the filtering surface. The deposited cake / solid is removed by scraping. 26
    • SOLID FLUID SEPARATION 27
    • SOLID FLUID SEPARATION VACUUM FILTERS ( SUCTION FILTERS ) ELECTROPHORETIC FILTERS – Intermittent / continuous operation. Electrophoresis is the motion of dispersed particles relative to a fluid under the influence of a spatially uniform electric field. Clay particles dispersed in water migrate when a constant electric field is applied. Liquid to be filtered DC is applied to a suspension of clay in water . Kaoline and other particles migrate to one of the electrodes. They get deposited there as a layer . The filter cake is removed. 28
    • DUST ELIMINATION 29
    • DUST ELIMINATION THE EFFLUENT GASES FROM THE MINERAL DRESSING PLANT SHOULD BE CLEANED TO REMOVE DUST PARTICLES. Dust is made of particles less than 10 micron size. They can remain in suspension for any length of time. They cause diseases. They are removed from air by 1. FLOCCULATION and SETTLING or 2. FILTERING . 1. DUST ELIMINATION BY SETTLING. Clean gas out Pass the dust containing air / gas through a large chamber. Effluent gas in Chamber The dust settles in the chamber. Not very efficient. settled dust Cyclonic Dust Collector is more efficient. The dust containing air / gas may be passed through a CYCLONE. The centrifugal forces and the gravitational forces allow the dust particles to settle. 30
    • DUST ELIMINATION 2. DUST ELIMINATION BY FLOCCULATION and SETTLING- ELECTROSTATIC PRECIPITATOR. Pass High voltage between an array of plates and grid. Pass the dust laden gas through charged plates. Negative ions flow to the plates and charge the gas-flow particles. The ionized particles move to the grounded plates. Particles build up on the collection plates and form a layer. They flocculate and settle at the bottom of the chamber. The layer does not collapse due to electrostatic pressure . 31
    • ELECTROSTATIC SEPARATOR 32
    • DUST ELIMINATION 3. DUST ELIMINATION BY SYNTHETIC FOG AND RAINS. Water acts as a bond between particles. A curtain of rain is created across the dust carrying gas stream. The muddy water is collected. The water is filtered to separate solids. The clean water is reused. 4. FILTERS ( Bag House ) . The gas is passed through the bags. They retain the dust particles. Clean gas goes out as exhaust. 33
    • DRYING 34
    • DRYING The solids are separated from the liquid by evaporation method. 1. Flash DryingThe wet material is fed into a tower. A current of hot gases rises from below in the tower. This dries the material 35
    • DRYING The solids are separated from the liquid by evaporation method. 2. Rotary Drying. The material is turned in a horizontal cylindrical drier. A current of hot gases is used to dry. 3. Hearth Drying. The material to be dried is turned over mechanically on a horizontal hearth. Heating is done by a current of hot air. 36
    • THANK YOU 37