basics in mineral processing-introduction1

8/8/2019 Basics in Mineral Processing-Introduction1

1/9Product Handbook 2:1

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


2/92:2 Product Handbook



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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

basics in mineral processing-introduction1

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