Basics in Mineral Processing-Introduction1
Transcript of Basics in Mineral Processing-Introduction1
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Minerals in Operation
BASICS IN MINERAL PROCESSING
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Operation Stages
The operating stages in minerals processing have remained the same forthousands of years. Of course we have come far in development of equipment andprocesses since then, but the hard, abrasive and inhomogeneous mineral crystalshave to be treated in special ways in order to extract maximum value out of eachsize fraction.
The operation pattern below has been used since the days of mineralis antiqua
Front service: Starting point of mineral processing
Size reduction & control: Processes to produce requested size distributionsfrom feed material
Enrichment: Processes to improve value of minerals by washingand/or separation
Upgrading: Processes to produce requested end products fromvalue and waste minerals.
Materials Handling: Operations for moving the processes forward with aminimum of flow disturbances
Protection: Measures to protect the process environment abovefrom wear and emissions of dust and sound
Operation Dry or Wet ?
FRONTSERVICE
SIZEREDUCTION
ANDCONTROL
ENRICHMENT UPGRADING
MATERIALS HANDLING
PROTECTION
Note! Wear rate is generally higher in wet processing!
In all other cases due to: Better efficiency More compact installation No dusting
When no water is needed forprocessing
When no water is allowed forprocessing
Dry processing Wet processing
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Mining and Quarry Fronts
The mining and quarry fronts are the starting points for recovery of rock andmineral values from surface and underground deposits.
Operations are drilling (blasting), primary crushing (optional) and materialshandling, dry and wet.
Underground
Natural Fronts
In the glacial, alluvial and marine fronts nature has done most of the primary sizereduction work.
Raw material such as gravel, sand and clay are important for processing of
construction ballast, metals and industrial mineral fillers.Operations are materials handling (wet and dry) and front crushing (optional).
Glacial
Glacial sand and gravel occur in areas which are or have been covered byice. The material is rounded and completely unsorted with an heterogeneous sizedistribution which ranges from boulders larger than 1 m (3 ft) down to silt (2-20microns). Clay contamination is concentrated in well defined layers.
Open pit
Mining and quarrying
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Marine
Marine sand and gravel often have a more limited size distribution than othertypes of sand and gravel. The minerals in marine sand and gravel have survivedthousands or even millions of years of natural attrition, from erosion in themountain ranges and grinding during transport down to the sea. The particles havebecome well rounded and the clay content is extremely low. Marine fronts are in
certain areas hosting heavy minerals like hematite, magnetite, rutile a.o.
Alluvial
The size of alluvial sand and gravel depends on the flow velocity of the water,among other things. Normally the maximum size is around 100 mm (4). Alluvialsand and gravel have a homogeneous size distribution and larger particles oftenhave high silica content. The clay content is often high, normally in the range of5 to 15 %. Alluvial fronts are in certain areas hosting gold, tin and preciousstones.
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Size Reduction
Crushing of rock and minerals
By tonnage this is by far the largest process operation in minerals processing. Thegoal is to produce rock or (more seldom) mineral fractions to be used as rock fillor ballast material for concrete and asphalt production. Quality parameters are
normally strength, size and shape. The size fractions, see below, are pricedaccording to defined size intervals and can be reached by crushing only, seesection 3.
>1000 >500 >100 >80 64 32 22 16 11 8 4 0 Size mm
PRIMARYGYRATORYCRUSHER
JAWCRUSHER
CRUSHERS
CONE CRUSHERSECONDARY
VSI
CONECRUSHERTERTIARY
Product value
1 m 100 mm 1 0 mm 1 mm 100 micron 10 micron 1 micron
100 micron
PRIMARY GYRATORYCRUSHER
JAWCRUSHER VSI
CONECRUSHER
CRUSHERS/ IMPACTORS
MILLS
VIBRATINGMILL
VERTIMILL
Crushing and grinding of ore and minerals
Size reduction of ores is normally done in order to liberate the value mineralsfrom the host rock. This means that we must reach the liberation size, normally inthe interval 100 10 micron, see value curve 1.If the raw material is a single mineral (Calcite, Feldspar a.o.) the value normallylays in the production of very fine powder (filler), see value curve 2.In order to maximise the value in size reduction of rock and minerals, see below,we need both crushing and grinding in various combinations, see section 3.
AG/SAG
PEBBLE
BALL
ROD
1.
2.
Size8
IMPACTORS
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1 m 10 mm 10 mm 1 mm 100 micron 10 micron 1 micron
100 micron
Size Control
Neither crushers nor grinding mills are very precise when it comes to the correctsizing of the end products. The reason is to find partly in the variation of themineral crystals compounds (hard-soft, abrasive non abrasive), partly in thedesign and performance of the equipment.
Size control is the tool for improvement of the size fractions in the processstages and in the final products.For the coarser part of the process, screens are used (in practise above 1-2mm).In the finer part we have to use classification with spiral classifiers and/orhydrocyclones, see section 4.
Enrichment Washing
Washing is the simplest method of enrichment used to improve the value of rockand mineral fractions from sand size and upwards. Removing of surface impuritieslike clay, dust, organics or salts is often a must for a saleable product.Different techniques are used depending on how hard these impurities areattached to the rock or mineral surface, see section 5.
Washing using
Wet screens Scrubbers Attrition cells Gravity beds
Size 8
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Enrichment Separation
Most value minerals (both metallic and industrial) are priced by their purity. Afterliberation by size reduction and size control all minerals are free to be separatedfrom each other.
Depending on the properties of the individual minerals they can be recovered bydifferent methods of separation, see section 5.
DEWATERING BYPRESSURE FILTERS
DEWATERING BY VACUUM FILTERS
SEDIMENTATION
SINTERING
DEWATERINGBY TUBEPRESSES
DEWATERING BY SCREENS
DEWATERING BY SPIRALS
Size 100 mm 10 mm 1 mm 100 micron 10 micron 1 micron
Upgrading
After the enrichment operation we end up with a value product (concentrate) and anon-value product (tailings).
These products are probably not sellable nor disposable due to the content ofprocess water, particle size, or chemical composition.
By upgrading we mean the methods of increasing the value of these products bysedimentation, mechanical dewatering, drying, calcining or sintering and recover-ing the process water from the tailings, making them disposable, see section 6.
Gravimetric Flotation Magnetic Leaching
N SH SO2 4
Upgrading by methods
DRYING
Gravity
Air
= value mineral
CALCINING
RELATIVE COST
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Materials Handling
Without a proper set up for materials handling no processing system willperform. Different process stages may be in various locations, may havevarious feed conditions, are on different shift cycles etc.
Materials handling of dry material is based on the operations of loadng,unloading, transportation, storing and feeding, see section 7.
Materials handling of wet material, called slurry handling is also based on theoperations of transportation (by slurry pumps and hoses), feeding (by slurrypumps) and storage (by slurry agitation), see section 8.
Store
Tra
nspo
rt
Feedop
etc.op
Unload
op
op
Transport Transp
ortStore
Store
Feed
Feedetc.
Dry handling
Slurry handling
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Wear in Operation
Whenever energy in any form penetrates rock, ore or mineral, wear will appear.
There is of course a difference whether the minerals are hard or soft, small orlarge, wet or dry, but wear will always be around. Both machines and structuresmust be protected from wear using metals, polymers or compound material.
See section 9, wear in operation.
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Operation and Environment
If wear is dangerous for equipment and structures, dust and noise is primarily adanger to the operators.
Dust is a problem to both equipment and operators in dry processing
Noise is a problem to operators both in wet and dry processing.
By tradition, the environment in mineral processing has a bad reputation.
This is now changing fast due to harder restrictions by law and harder demandsfrom the operators, see section 10, Operation and environment.
VOLUME x PRICE COSTS + MOTIVATION = S
Operation Values
Prices for products from your operation are seldom set by yourself, but by themarket buying them. There is always a possibility to increase the income fromyour operation by added values generated by the operation itself.
By improving the output we can increase the product volumes
By improving the quality we can increase the price of our products
By improving the cost control we can reduce our costs of operation
By improving the comfort for our operators we can improve motivationand reduce disturbances in operation
This can be done by small adjustments, by improved service or by reinvest-
ment in more effective equipment, see all sections.
Added value in operation
Output Quality Cost Control Comfort
AVAILABILITY(up time)
SIZE /SHAPE
CAPITAL SECURITY
CAPACITYPURITY /
RECOVERYENERGY ENVIRON-
MENT
FLEXIBILITY
COMPAC-TION /
DENSITY
MATERIALRELATIONS