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mineral beneficiation-170906180924.pdf...................

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Bimal Dey
Bimal Dey

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MINERAL BENEFICIATION A SEMINAR PRESENTATION ON
CONTENTS • INTRODUCTION • DIFFERENT PROCESS OF MINERAL BENIFICATION COMMINUTION & SIZING GRAVITY CONCENTRATION MAGNETIC CONCENTRATION ELECTROSTATIC CONCENTRATION FROTH FLOTATION COMPLEX MINERAL PROCESSING PLANT • OBJECTIVE OF MINERAL BENEFICATION • IMPACT OF MINERAL BENEFICATION ON THE ENVIRONMENT • CONCLUSSION • REFFERENCE
INTRODUCTION • MINERAL BENEFICIATION IS THE PROCESS BY WHICH THE VALUABLE CONSTITUENTS OF THE ORE ARE CONCENTRATED BY MEANS OF PHYSICAL SEPARATION. IT IS ONE OF THE INITIAL STEPS BEFORE METALLURGY AND IS AN IMPORTANT STEP IN EXTRACTING METALS FROM NATURAL RESOURCES. • THESE INCLUDES ALL THE PROCESSES WHICH DEALS WITH SEPARATION OF ORE MINERAL FROM GANGUES OR TAILING AND CONCENTRATION OF THE ORE MINERAL. • THE OTHER PHYSICAL PROCESSES LIKE TRANSPORTING, CRUSHING, GRINDING ETC. ARE ALSO INCLUDED.
DIFFERENT PROCESS OF MINERAL BENEFICIATION THE DIFFERENT PROCESSES ARE : • COMMINUTION & SIZING • GRAVITY CONCENTRATION • MAGNETIC CONCENTRATION • ELECTROSTATIC CONCENTRATION • FROTH FLOTATION • COMPLEX MINERAL PROCESSING PLANT
COMMINUTION AND SIZING • COMMINUTION IS THE BREAKING DOWN OF ORE MATERIAL. THEY MAY BE DONE EITHER IN DRY OR WET CONDITION. CRUSHING AND GRINDING ARE THE TWO PRIMARY COMMINUTION PROCESSES. THE PRIMARILY USED EQUIPMENT IN CRUSHING ARE-JAW CRUSHERS, GYRATORY CRUSHERS AND CONE CRUSHERS WHEREAS ROD MILLS AND BALL MILLS, CLOSED CIRCUITED WITH A CLASSIFIER UNIT, ARE GENERALLY EMPLOYED FOR GRINDING PURPOSES IN A MINERAL PROCESSING PLANT.
GRINDER
JAW CRUSSHERS
• SIZING SIZING IS THE GENERAL TERM FOR SEPARATION OF PARTICLES ACCORDING TO THEIR SIZE.IT IS DONE BY USING BAR SCREENS, WEDGE WIRE SCREENS, RADIAL SIEVES, BANANA SCREENS, MULTI-DECK SCREENS, VIBRATORY SCREEN, FINE SCREENS, FLIP FLOP SCREENS WIRE MESH SCREENS ETC. CLASSIFICATION EQUIPMENT MAY INCLUDE ORE SORTERS, GAS CYCLONES, HYDROCYCLONES, ROTATING TROMMELS, RAKE CLASSIFIERS OR FLUIDIZED CLASSIFIERS.
GRAVITY CONCENTRATION • GRAVITY SEPARATION IS THE SEPARATION OF TWO OR MORE MINERALS OF DIFFERENT SPECIFIC GRAVITY BY THEIR RELATIVE MOVEMENT IN RESPONSE TO THE FORCE OF GRAVITY AND ONE OR MORE OTHER FORCES (SUCH AS CENTRIFUGAL FORCES, MAGNETIC FORCES, BUOYANT FORCES), ONE OF WHICH IS RESISTANCE TO MOTION (DRAG FORCE) BY A VISCOUS MEDIUM SUCH AS HEAVY MEDIA, WATER OR, LESS COMMONLY, AIR.
• THIS METHOD IS USED WHEN THE ORE MATERIAL IS HEAVIER THAN THE GANGUE MATERIAL. THE FINELY POWDERED ORE IS WASHED DOWN THROUGH A STEAM OF WATER OVER VIBRATING SLOPED TABLE WITH LONG WOODEN STRIPES CALLED RIFFLES( FORMING GROOVES ). • THE HEAVIER ORE MATERIALS ARE OBSTRUCTED BY THE RIFFLES AND SETTLES DOWN THE GROOVES AND THE LIGHTER ONES ARE WASHED ALWAY. THESE ORE MATERIALS DEPOSITED ARE COLLECTED FROM THE GROOVES AND USED FOR FURTHER PROCESSING.
• OF THE GRAVITY SEPARATION PROCESSES, THE SPIRAL CONCENTRATORS AND CIRCULAR JIGS ARE TWO OF THE MOST ECONOMICAL DUE TO THEIR SIMPLICITY AND USE OF LITTLE SPACE. THEY OPERATE BY FLOWING FILM SEPARATION AND CAN EITHER USE WASHWATER OR BE WASHWATER-LESS. THE WASHWATER SPIRALS SEPARATE PARTICLES MORE EASILY BUT CAN HAVE ISSUES WITH ENTRAINMENT OF GANGUE WITH THE CONCENTRATE PRODUCED.
mineral beneficiation-170906180924.pdf...................
THE SPIRAL CONCENTRATORS
MAGNETIC CONCENTRATION • MAGNETIC SEPARATION IS A PROCESS IN WHICH MAGNETICALLY SUSCEPTIBLE MATERIAL IS EXTRACTED FROM A MIXTURE USING A MAGNETIC FORCE. THIS SEPARATION TECHNIQUE CAN BE USEFUL IN MINING IRON AS IT IS ATTRACTED TO A MAGNET. • MINERALS FALL INTO ONE OF THREE MAGNETIC PROPERTIES: FERROMAGNETIC PARAMAGNETIC DIAMAGNETIC
• FERROMAGNETIC MINERALS ARE THEMSELVES MAGNETIC (I.E., MAGNETITE AND PYRHOTITE) AND CAN BE EASILY SEPARATED FROM OTHER MINERALS WITH A MAGNET SINCE THEY WILL STICK TO THE POLES OF THE MAGNET. • PARAMAGNETIC AND DIAMAGNETIC MINERALS ARE NOT MAGNETIC, BUT THEY DIFFER IN HOW THEY INTERACT WITH A MAGNETIC FIELD. PARAMAGNETIC MINERALS ARE WEAKLY ATTRACTED INTO A MAGNETIC FIELD AND DIAMAGNETIC MINERALS ARE WEAKLY REPELLED BY A MAGNETIC FIELD. THUS, IF A MIXTURE OF PARAMAGNETIC AND DIAMAGNETIC MINERALS IS PASSED THROUGH A MAGNETIC FIELD, THEY WILL BE PULLED INTO THE FIELD (PARAMAGNETIC) OR REPELLED FROM THE FIELD (DIAMAGNETIC) AND MAY BE SEPARATED.
mineral beneficiation-170906180924.pdf...................
ELECTROSTATIC SEPARATION • ELECTROSTATIC SEPARATION WORKS BECAUSE DIFFERENT MINERALS HAVING DIFFERENT ELECTROSTATIC AFFINITIES WILL ABSORB DIFFERENT AMOUNT OF CHARGE DEPENDING UPON THEIR COMPOSITION, AND HENCE ARE DEFLECTED IN DIFFERENT MAGNITUDE BY AN ELECTRIC FIELD. • IN THIS METHOD, THE GRAINS AFTER SIEVED BY SIZE, THEY ARE PLACED THROUGH A BENEFICIATOR. AFTER A FEW PASSES THROUGH BENEFICIATORS , THE MINERALS WITH DIFFERENT ELECTROSTATIC AFFINITIES WILL BE SEPARATED. THE RESULTANT MATERIAL IS COLLECTED IN DIFFERENT BINS WHEREBY THE ENRICHED PORTION OF THE DESIRED MINERAL IS CALLED THE "CONCENTRATE" AND THE REST OF THE OUTPUT IS CALLED THE "GANGUE" OR "TAILINGS".
mineral beneficiation-170906180924.pdf...................
FROTH FLOTATION • FROTH FLOTATION IS AN IMPORTANT CONCENTRATION PROCESS. THIS PROCESS CAN BE USED TO SEPARATE ANY TWO DIFFERENT PARTICLES AND OPERATED BY THE SURFACE CHEMISTRY OF THE PARTICLES. IN FLOTATION, BUBBLES ARE INTRODUCED INTO A PULP AND THE BUBBLES RISE THROUGH THE PULP. IN THE PROCESS, HYDROPHOBIC PARTICLES BECOME BOUND TO THE SURFACE OF THE BUBBLES. • SULFIDE AND NON-SULFIDE MINERALS AS WELL AS NATIVE METALS ARE RECOVERED BY FROTH FLOTATION. THIS PROCESS IS BASED ON THE ABILITY OF CERTAIN CHEMICALS TO MODIFY THE SURFACE PROPERTIES OF THE MINERAL.
• DIFFERENT CHEMICALS ARE USED IN FROTH FLOTATION TO ENHANCE THE PROCESS. THEY ARE- A)FROTHERS (PINE OIL, ALCOHOL, LOW MOLECULAR WEIGHT POLYPROPYLENE GLYCOL) B)COLLECTORS (OILS, XANTHATES, DITHIOPHOSPHATES, PETROLEUM SULFONATES, FATTY AMINES) C)DEPRESSANTS(IRON SULPHIDES, DIETHYLENETETRAMINE, TRIETHYENETETRAMINE, CARBONCEOUS GANGUE DEPRESSANTS)
FLOTATION CHAMBER
mineral beneficiation-170906180924.pdf...................
FROTH FLOTATION IN MNEERAL PROCESSING PLANT
COMPLEX MINERAL PROCESSING PLANT • IN THIS METHOD TWO OR MORE MINERAL SEPARATION METHODS ARE COMBINED TO CONCENTRATE THE DESIRED MINERAL. THEY ARE USED IN MIXED MINES WHERE THE ORES ARE MIXED. • SOME OF THE MIXED TECHNOLOGIES ARE- A) FLOTATION AND GRAVITY SEPARATION B) FLOTATION AND MAGNETIC SEPARATION C) GRAVITY AND MAGNETIC SEPARATION D) FLOTATION GRAVITY FLOTATION AND MAGNETIC SEPARATION
OBJECTIVE OF MINERAL BENEFICATION • TO INCREASE THE METAL CONTENT OF THE ORE. • TO REDUCE THE GANGUE CONTENT SO AS TO LOWER THE SLAG FORMED IN EXTRACTION OF METAL. • TO DECREASE THE THERMAL ENERGY REQUIRED TO SEPARATE LIQUID METAL FROM MINERAL
IMPACT OF MINERAL BENEFICATION ON THE ENVIRONMENT • POLLUTION OF WATER BY EFFLUENTS FROM RESIDUAL LIQUIDS OF FROTH FLOTATION AND ALSO BY WASHING OF ORE MATERIAL. • NOISE IS PRODUCED BY GRINDING BLASTING ETC. AND BY THE HEAVY MACHINERIES USED IN THE BENEFICIATION PROCESS. • DESTRUCTION OF LAND BY IMPROPER DUMPING OF GANGUE MATERIAL. • ENERGY A HUGE AMOUNT OF ENERGY IS WASTED IS THE TECHNOLOGY USED FOR PROCESSING IS OUTDATES.
CONCLUSSION AN ORE IS A NATURALLY OCCURING MATRERIAL WHOSE METALIC MINERAL CONTENT IS HIGH. THE PROCESS BY WHICH VALUABLE CONTENT OF AN ORE IS CONCENTRATED OR SEPARATED BY MEANS OF PHYSICAL SEPARATON IS KNOWN AS MINERAL BENEFICIATION. AMONG THE VARIOUS TYPES OF METHODS USED SUITABLE ONES ARE TO BE CHOSEN TO CONCENTRATE THE MINERAL CONTENT FROM THE ORE BASED UPON THE NATURE OF THE ORE. THE PORCESS OF MINERAL BENIFICIATION CAUSES SERIOUS ENVIRONMENTAL CONCERNS AND MUST NOT BE OVERLOOKED. NECESSARY STEPS MUST BE TAKEN UP DURING AND AFTER TO EDUC SUCH RISK.
REFFERENCE • MINERAL PROCESSING- BY M R PYROR • MINERAL PROCESSING- BY SK JAIN • HTTPS://EN.WIKIPEDIA.ORG/WIKI/MINERAL_PROCESSING • HTTP://WWW.TULANE.EDU/~SANELSON/ • HTTP://EPSC.WUSTL.EDU/GEOCHRONOLOGY/FRANTZ.HTM

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mineral beneficiation-170906180924.pdf...................

  • 2. CONTENTS • INTRODUCTION • DIFFERENT PROCESS OF MINERAL BENIFICATION COMMINUTION & SIZING GRAVITY CONCENTRATION MAGNETIC CONCENTRATION ELECTROSTATIC CONCENTRATION FROTH FLOTATION COMPLEX MINERAL PROCESSING PLANT • OBJECTIVE OF MINERAL BENEFICATION • IMPACT OF MINERAL BENEFICATION ON THE ENVIRONMENT • CONCLUSSION • REFFERENCE
  • 3. INTRODUCTION • MINERAL BENEFICIATION IS THE PROCESS BY WHICH THE VALUABLE CONSTITUENTS OF THE ORE ARE CONCENTRATED BY MEANS OF PHYSICAL SEPARATION. IT IS ONE OF THE INITIAL STEPS BEFORE METALLURGY AND IS AN IMPORTANT STEP IN EXTRACTING METALS FROM NATURAL RESOURCES. • THESE INCLUDES ALL THE PROCESSES WHICH DEALS WITH SEPARATION OF ORE MINERAL FROM GANGUES OR TAILING AND CONCENTRATION OF THE ORE MINERAL. • THE OTHER PHYSICAL PROCESSES LIKE TRANSPORTING, CRUSHING, GRINDING ETC. ARE ALSO INCLUDED.
  • 4. DIFFERENT PROCESS OF MINERAL BENEFICIATION THE DIFFERENT PROCESSES ARE : • COMMINUTION & SIZING • GRAVITY CONCENTRATION • MAGNETIC CONCENTRATION • ELECTROSTATIC CONCENTRATION • FROTH FLOTATION • COMPLEX MINERAL PROCESSING PLANT
  • 5. COMMINUTION AND SIZING • COMMINUTION IS THE BREAKING DOWN OF ORE MATERIAL. THEY MAY BE DONE EITHER IN DRY OR WET CONDITION. CRUSHING AND GRINDING ARE THE TWO PRIMARY COMMINUTION PROCESSES. THE PRIMARILY USED EQUIPMENT IN CRUSHING ARE-JAW CRUSHERS, GYRATORY CRUSHERS AND CONE CRUSHERS WHEREAS ROD MILLS AND BALL MILLS, CLOSED CIRCUITED WITH A CLASSIFIER UNIT, ARE GENERALLY EMPLOYED FOR GRINDING PURPOSES IN A MINERAL PROCESSING PLANT.
  • 8. • SIZING SIZING IS THE GENERAL TERM FOR SEPARATION OF PARTICLES ACCORDING TO THEIR SIZE.IT IS DONE BY USING BAR SCREENS, WEDGE WIRE SCREENS, RADIAL SIEVES, BANANA SCREENS, MULTI-DECK SCREENS, VIBRATORY SCREEN, FINE SCREENS, FLIP FLOP SCREENS WIRE MESH SCREENS ETC. CLASSIFICATION EQUIPMENT MAY INCLUDE ORE SORTERS, GAS CYCLONES, HYDROCYCLONES, ROTATING TROMMELS, RAKE CLASSIFIERS OR FLUIDIZED CLASSIFIERS.
  • 9. GRAVITY CONCENTRATION • GRAVITY SEPARATION IS THE SEPARATION OF TWO OR MORE MINERALS OF DIFFERENT SPECIFIC GRAVITY BY THEIR RELATIVE MOVEMENT IN RESPONSE TO THE FORCE OF GRAVITY AND ONE OR MORE OTHER FORCES (SUCH AS CENTRIFUGAL FORCES, MAGNETIC FORCES, BUOYANT FORCES), ONE OF WHICH IS RESISTANCE TO MOTION (DRAG FORCE) BY A VISCOUS MEDIUM SUCH AS HEAVY MEDIA, WATER OR, LESS COMMONLY, AIR.
  • 10. • THIS METHOD IS USED WHEN THE ORE MATERIAL IS HEAVIER THAN THE GANGUE MATERIAL. THE FINELY POWDERED ORE IS WASHED DOWN THROUGH A STEAM OF WATER OVER VIBRATING SLOPED TABLE WITH LONG WOODEN STRIPES CALLED RIFFLES( FORMING GROOVES ). • THE HEAVIER ORE MATERIALS ARE OBSTRUCTED BY THE RIFFLES AND SETTLES DOWN THE GROOVES AND THE LIGHTER ONES ARE WASHED ALWAY. THESE ORE MATERIALS DEPOSITED ARE COLLECTED FROM THE GROOVES AND USED FOR FURTHER PROCESSING.
  • 11. • OF THE GRAVITY SEPARATION PROCESSES, THE SPIRAL CONCENTRATORS AND CIRCULAR JIGS ARE TWO OF THE MOST ECONOMICAL DUE TO THEIR SIMPLICITY AND USE OF LITTLE SPACE. THEY OPERATE BY FLOWING FILM SEPARATION AND CAN EITHER USE WASHWATER OR BE WASHWATER-LESS. THE WASHWATER SPIRALS SEPARATE PARTICLES MORE EASILY BUT CAN HAVE ISSUES WITH ENTRAINMENT OF GANGUE WITH THE CONCENTRATE PRODUCED.
  • 14. MAGNETIC CONCENTRATION • MAGNETIC SEPARATION IS A PROCESS IN WHICH MAGNETICALLY SUSCEPTIBLE MATERIAL IS EXTRACTED FROM A MIXTURE USING A MAGNETIC FORCE. THIS SEPARATION TECHNIQUE CAN BE USEFUL IN MINING IRON AS IT IS ATTRACTED TO A MAGNET. • MINERALS FALL INTO ONE OF THREE MAGNETIC PROPERTIES: FERROMAGNETIC PARAMAGNETIC DIAMAGNETIC
  • 15. • FERROMAGNETIC MINERALS ARE THEMSELVES MAGNETIC (I.E., MAGNETITE AND PYRHOTITE) AND CAN BE EASILY SEPARATED FROM OTHER MINERALS WITH A MAGNET SINCE THEY WILL STICK TO THE POLES OF THE MAGNET. • PARAMAGNETIC AND DIAMAGNETIC MINERALS ARE NOT MAGNETIC, BUT THEY DIFFER IN HOW THEY INTERACT WITH A MAGNETIC FIELD. PARAMAGNETIC MINERALS ARE WEAKLY ATTRACTED INTO A MAGNETIC FIELD AND DIAMAGNETIC MINERALS ARE WEAKLY REPELLED BY A MAGNETIC FIELD. THUS, IF A MIXTURE OF PARAMAGNETIC AND DIAMAGNETIC MINERALS IS PASSED THROUGH A MAGNETIC FIELD, THEY WILL BE PULLED INTO THE FIELD (PARAMAGNETIC) OR REPELLED FROM THE FIELD (DIAMAGNETIC) AND MAY BE SEPARATED.
  • 17. ELECTROSTATIC SEPARATION • ELECTROSTATIC SEPARATION WORKS BECAUSE DIFFERENT MINERALS HAVING DIFFERENT ELECTROSTATIC AFFINITIES WILL ABSORB DIFFERENT AMOUNT OF CHARGE DEPENDING UPON THEIR COMPOSITION, AND HENCE ARE DEFLECTED IN DIFFERENT MAGNITUDE BY AN ELECTRIC FIELD. • IN THIS METHOD, THE GRAINS AFTER SIEVED BY SIZE, THEY ARE PLACED THROUGH A BENEFICIATOR. AFTER A FEW PASSES THROUGH BENEFICIATORS , THE MINERALS WITH DIFFERENT ELECTROSTATIC AFFINITIES WILL BE SEPARATED. THE RESULTANT MATERIAL IS COLLECTED IN DIFFERENT BINS WHEREBY THE ENRICHED PORTION OF THE DESIRED MINERAL IS CALLED THE "CONCENTRATE" AND THE REST OF THE OUTPUT IS CALLED THE "GANGUE" OR "TAILINGS".
  • 19. FROTH FLOTATION • FROTH FLOTATION IS AN IMPORTANT CONCENTRATION PROCESS. THIS PROCESS CAN BE USED TO SEPARATE ANY TWO DIFFERENT PARTICLES AND OPERATED BY THE SURFACE CHEMISTRY OF THE PARTICLES. IN FLOTATION, BUBBLES ARE INTRODUCED INTO A PULP AND THE BUBBLES RISE THROUGH THE PULP. IN THE PROCESS, HYDROPHOBIC PARTICLES BECOME BOUND TO THE SURFACE OF THE BUBBLES. • SULFIDE AND NON-SULFIDE MINERALS AS WELL AS NATIVE METALS ARE RECOVERED BY FROTH FLOTATION. THIS PROCESS IS BASED ON THE ABILITY OF CERTAIN CHEMICALS TO MODIFY THE SURFACE PROPERTIES OF THE MINERAL.
  • 20. • DIFFERENT CHEMICALS ARE USED IN FROTH FLOTATION TO ENHANCE THE PROCESS. THEY ARE- A)FROTHERS (PINE OIL, ALCOHOL, LOW MOLECULAR WEIGHT POLYPROPYLENE GLYCOL) B)COLLECTORS (OILS, XANTHATES, DITHIOPHOSPHATES, PETROLEUM SULFONATES, FATTY AMINES) C)DEPRESSANTS(IRON SULPHIDES, DIETHYLENETETRAMINE, TRIETHYENETETRAMINE, CARBONCEOUS GANGUE DEPRESSANTS)
  • 23. FROTH FLOTATION IN MNEERAL PROCESSING PLANT
  • 24. COMPLEX MINERAL PROCESSING PLANT • IN THIS METHOD TWO OR MORE MINERAL SEPARATION METHODS ARE COMBINED TO CONCENTRATE THE DESIRED MINERAL. THEY ARE USED IN MIXED MINES WHERE THE ORES ARE MIXED. • SOME OF THE MIXED TECHNOLOGIES ARE- A) FLOTATION AND GRAVITY SEPARATION B) FLOTATION AND MAGNETIC SEPARATION C) GRAVITY AND MAGNETIC SEPARATION D) FLOTATION GRAVITY FLOTATION AND MAGNETIC SEPARATION
  • 25. OBJECTIVE OF MINERAL BENEFICATION • TO INCREASE THE METAL CONTENT OF THE ORE. • TO REDUCE THE GANGUE CONTENT SO AS TO LOWER THE SLAG FORMED IN EXTRACTION OF METAL. • TO DECREASE THE THERMAL ENERGY REQUIRED TO SEPARATE LIQUID METAL FROM MINERAL
  • 26. IMPACT OF MINERAL BENEFICATION ON THE ENVIRONMENT • POLLUTION OF WATER BY EFFLUENTS FROM RESIDUAL LIQUIDS OF FROTH FLOTATION AND ALSO BY WASHING OF ORE MATERIAL. • NOISE IS PRODUCED BY GRINDING BLASTING ETC. AND BY THE HEAVY MACHINERIES USED IN THE BENEFICIATION PROCESS. • DESTRUCTION OF LAND BY IMPROPER DUMPING OF GANGUE MATERIAL. • ENERGY A HUGE AMOUNT OF ENERGY IS WASTED IS THE TECHNOLOGY USED FOR PROCESSING IS OUTDATES.
  • 27. CONCLUSSION AN ORE IS A NATURALLY OCCURING MATRERIAL WHOSE METALIC MINERAL CONTENT IS HIGH. THE PROCESS BY WHICH VALUABLE CONTENT OF AN ORE IS CONCENTRATED OR SEPARATED BY MEANS OF PHYSICAL SEPARATON IS KNOWN AS MINERAL BENEFICIATION. AMONG THE VARIOUS TYPES OF METHODS USED SUITABLE ONES ARE TO BE CHOSEN TO CONCENTRATE THE MINERAL CONTENT FROM THE ORE BASED UPON THE NATURE OF THE ORE. THE PORCESS OF MINERAL BENIFICIATION CAUSES SERIOUS ENVIRONMENTAL CONCERNS AND MUST NOT BE OVERLOOKED. NECESSARY STEPS MUST BE TAKEN UP DURING AND AFTER TO EDUC SUCH RISK.
  • 28. REFFERENCE • MINERAL PROCESSING- BY M R PYROR • MINERAL PROCESSING- BY SK JAIN • HTTPS://EN.WIKIPEDIA.ORG/WIKI/MINERAL_PROCESSING • HTTP://WWW.TULANE.EDU/~SANELSON/ • HTTP://EPSC.WUSTL.EDU/GEOCHRONOLOGY/FRANTZ.HTM