Minerals in Operation Operation Stages The operating stages in minerals processing have remained the same for thousands of years. Of course we have come far in development of equipment and processes since then, but the hard, abrasive and inhomogeneous mineral crystals have to be treated in special ways in order to extract maximum value out of each size fraction. The operation pattern below has been used since the days of “mineralis antiqua”
PROTECTION
FRONT SERVICE
SIZE REDUCTION AND CONTROL
ENRICHMENT
UPGRADING
MATERIALS MA TERIALS HANDLING
Starting point of mineral processing Front service: Size reduction & control: Processes to produce requested size distributions from feed material Processes to improve value of minerals by washing Enrichment: and/or separation Upgrading: Processes to produce requested end products from value and waste minerals. Operations for moving the processes forward with a Materials Handling: minimum of flow disturbances Protection: Measures to protect the process environment above from wear and emissions of dust and sound
Operation – Dry or Wet ?
Dry processing • Wh When en no wa wate terr is is nee neede ded d for for processing • Wh When en no no wat water er is al allo lowe wed d for for processing
Wet processing In all other cases due to: • Be Bettte terr ef effi fici cien ency cy • Mo More re com compa pact ct ins insta tallllat atio ionn • No dusting
Note! Wear rate is is generally higher in wet processing! processing!
BASICS IN MINERAL PROCESSING
Product Handbook 2:1
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Minerals in Operation Mining and Quarry Fronts The mining and quarry fronts are the starting points for recovery of rock and mineral values from surface and underground deposits. n n i o s i l t a a r r e e n p i O M
Operations are drilling (blasting), primary crushing (optional) and materials handling, dry and wet. Mining and quarrying
Open pit
Natural Fronts
Underground
In the glacial, alluvial and marine fronts nature has done most of the primary size reduction 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 by ice. The material is rounded and completely unsorted with an heterogeneous size distribution which ranges from boulders larger than 1 m (3 ft) down to silt (2-20 microns). Clay contamination is concentrated in well defined layers.
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BASICS IN MINERAL PROCESSING
Minerals in Operation
n n i o i s t l a a r r e e n p i O M
Alluvial The size of alluvial sand and gravel depends on the flow velocity of the water, among other things. Normally the maximum size is i s around 100 mm (4”). Alluvial sand and gravel have a homogeneous size distribution and larger particles often have high silica content. The clay content is often high, normally in the range of 5 to 15 %. Alluvial fronts are in certain areas hosting gold, tin and precious stones.
Marine Marine sand and gravel often have a more limited size distribution than other types of sand and gravel. The minerals in marine sand and gravel have survived thousands – or even millions of years – of natural attrition, from erosion in the mountain ranges and grinding during transport down to the sea. The particles have become well rounded and the clay content is extremely low. Marine fronts are in certain areas hosting heavy minerals like hematite, magnetite, rutile a.o.
BASICS IN MINERAL PROCESSING
Product Handbook 2:3
Minerals in Operation Size Reduction Crushing of rock and minerals n n i o s i l t a a r r e e n p i O M
By tonnage this is by far the largest process operation in minerals processing. The goal is to produce rock or (more seldom) mineral fractions to be used as rock fill or ballast material for concrete and asphalt production. Quality parameters are normally strength, size and shape. The size fractions, see below, are priced according to defined size intervals and can be reached by crushing only, see section 3. PRIMARY GYRATORY CRUSHER
CONE CRUSHER SECONDARY
IMPACTORS Product value
CONE CRUSHER TERTIARY
CRUSHERS
JAW CRUSHER
VSI
>1000 >500 >100 >80
64
32
22
16
11
8
4
0
Size mm
Crushing and grinding of ore and minerals Size reduction of ores is normally done in order to liberate the value minerals from the host rock. This means that we must reach the liberation size, normally in the interval 100 – 10 micron, see value curve 1. If the raw material is a single mineral (Calcite, Feldspar a.o.) the value normally lays 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. PRIMARY GYRATORY CRUSHER CONE CRUSHER
AG/SAG
1.
CRUSHERS / IMPACTORS CRUSHERS /
VERTIMILL
2.
ROD RO D
MILLS
BALL
PEBBLE JAW CRUSHER
Size
8 1 m
VSI
100 10 0 mm
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1 0 mm
1 mm
VIBRATING MILL
100 micron
100 mic micron ron
10 mic micron ron
1 mic micron ron
BASICS IN MINERAL PROCESSING
Minerals in Operation Size Control Neither crushers nor grinding mills are very precise when it comes to the correct sizing of the end products. The reason is to find partly in the variation of the mineral crystals compounds (hard-soft, abrasive – non abrasive), partly in the design and performance of the equipment.
Size control is the tool for improvement of the size fractions in the process stages 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/or hydrocyclones, see section 4.
100 micron
Size
8
1m
10 mm
10 mm
1 mm
100 micron
10 micron
1 micron
Enrichment – Washing Washing is the simplest method of enrichment used to improve the value of rock and mineral fractions from sand size and upwards. Removing of surface impurities like clay, dust, organics or salts is often a must for a saleable product. Different techniques are used depending on how hard these impurities are attached to the rock or mineral surface, see section 5.
Washing using Wet screens
Scrubbers
BASICS IN MINERAL PROCESSING
Attrition cells
Gravity beds
Product Handbook 2:5
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Minerals in Operation Enrichment – Separation Most value minerals (both metallic and industrial) are priced by their purity. After liberation by size reduction and size control all minerals are free to be separated from each other. n n i o s i l t a a r r e e n p i O M
Depending on the properties of the individual minerals they can be recovered by different methods of separation, see section 5. Gravimetric
Flotation
Magnetic
Leaching
N H2 SO4
Gravity Air
• = value mineral Upgrading After the enrichment operation we end up with a value product (concentrate) and a non-value product (tailings). These products are probably not sellable nor disposable due to the content of process water, particle size, or chemical composition. By upgrading we mean me an the methods of increasing the value of these products by sedimentation, mechanical dewatering, drying, calcining or sintering and recovering the process water from the tailings, making them disposable, see section 6.
Upgrading by methods RELATIVE COST
SINTERING
CALCINING
DRYING DEWATERING BY TUBE PRESSES DEWATERING BY PRESSURE FILTERS DEWATERING BY VACUUM FILTERS DEWATERING BY SCREENS DEWATERING BY SPIRALS SEDIMENTATION Size
100 mm
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10 mm
1 mm
100 micron
10 micron
1 micron
BASICS IN MINERAL PROCESSING
Minerals in Operation Materials Handling Without a proper set up for materials handling no processing system will perform. Different process stages may be in various locations, may have various feed conditions, are on different shift cycles etc. n n i o i s t l a a r r e e n p i O M
load íng, Materials handling of dry material is based on the operations of loadíng, unloading, transportation, storing and feeding, see section 7. Materials handling of wet material, called slurry handling is also based on the operations of transportation (by slurry pumps and hoses), feeding (by slurry pumps) and storage (by slurry agitation), see section 8.
Dry handling
Unload
o r t T r a n s p
Store
o r t T r a n s p Store
op Feed
etc.
op
F e e d
Slurry handling
t r p o s n a r T
Store
op
BASICS IN MINERAL PROCESSING
e d e F
op
etc.
Product Handbook 2:7
Minerals in Operation Wear in Operation Whenever energy in any form penetrates rock, ore or mineral, wear will appear.
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There is of course a difference whether the minerals are hard or soft, small or large, wet or dry, but wear will always be around. Both machines and structures must be protected from wear using metals, polymers or compound material. See section 9, wear in operation.
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BASICS IN MINERAL PROCESSING
Minerals in Operation Operation and Environment If wear is dangerous for equipment and structures, dust and noise is primarily a danger to the operators. a nd operators in dry processing Dust is a problem to both equipment and
Noise is a problem to operators both in wet and a nd dry processing. By tradition, the environment in mineral processing has a bad reputation.
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This is now changing fast due to harder restrictions by law and harder demands from the operators, see section 10, Operation and environment.
Operation Values Prices for products from your operation are seldom set by yourself, but by the market buying them. There is always a possibility to increase the income from your operation by added values generated by the operation itself.
• • • •
By improv improving ing the outpu outputt we can can increa increase se the the product product volu volumes mes By improv improving ing the the quality quality we we can incr increase ease the price price of our our product productss By improv improving ing the the cost cost control control we we can redu reduce ce our our costs costs of operat operation ion By improvi improving ng the the comfort comfort for for our our operato operators rs we can can improv improve e motivati motivation on and reduce disturbances in operation This can be done by small adjustments, by improved service or by reinvestment in more effective equipment, see all sections. Added value in operation VOLUME x
PRICE
–
COSTS
+
MOTIVATION MOTIVA TION = S
Output
Quality
AVAILABILITY (up time)
SIZE / SHAPE
CAPITAL
SECURITY
CAPACITY
PURITY / RECOVERY
ENERGY
ENVIRONMENT
FLEXIBILITY
COMPACTION / DENSITY
MATERIAL
BASICS IN MINERAL PROCESSING
Cost Control
Comfort
RELATIONS
Product Handbook 2:9
