(8) Ore Processing (Beneficiation)

8/12/2019 (8) Ore Processing (Beneficiation)

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Mineral dressing

(= Ore beneficiation)The first process most ores undergo after t

the mine is mineral dressing (processingcalled ore preparation, milling, and ore dore beneficiation.

Ore dressing is a process of mechanically the grains of ore minerals from the gangminerals, to produce a concentrate (enric

portion) containing most of the ore minetailing (discard) containing the bulk of tminerals.


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Mineral dressing

Since most ore minerals are usuadisseminated and intimately associgangue minerals, the various mineral

broken apart (freed) or liberatedbefor

be collected in separate products.

Therefore, the first part in any ore dressiwill involve the crushing and grindingalso known by a common namcomminution

) of the ore to a point wmineral grain is practically free.


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Crushin


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Comminution

Crushing and grinding are usually carried out in a seoperations by which the lump size is reduced step byare 3 stages of crushing and 2 stages of grinding.

i. Primary Crushing (coarse crushing): In primarore or run-of-mine ore (up to 1 m in size) is crushabout 10 cm and it is done in a jaw or gyratory cr

ii. Secondary Crushing (intermediate crushing): Iore is crushed from 10 cm to less than 1 2 cm sipurpose jaw, cone or roll crushers are used. Thescrushers consume more power than primary cru

iii. Tertiary Crushing (fine crushing): By tertiaryis crushed from 1 2 cm to less than 0.5 cm. Shorcrushers, roll crushers, hammer mills can be usedpurpose.


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Comminution The two stages of grinding are:

i. Coarse Grinding: Rod mills are generallygrinding machines. They are capable of takas 50 mm and making a product as fine as 3

ii. Fine Grinding: Fine grinding, which is thcomminution, is performed in ball mills usinthe grinding medium. The ball mill, after fematerial may give a product that is less thanGrinding is usually done wet.

The principle purposes of grinding are:

i. To obtain the correct degree of liberation in minera

ii. To increase the specific surface area of the valuablhydrometallurgical treatment; i.e. leaching.


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The mills


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Sizing Methods There are two methods of industrial sizing.

i. Screening

ii. Classification

Screening is generally carried out on relatively coarse mefficiency decreases rapidly with fineness. Screening is gmaterials above about 250 microns in size, finer sizing nundertaken by classification.

Classification: Classification is defined as a method of seof mineral particles into two or more products accordinvelocities in water, in air or in other fluids as given in beIndustrial classification may be carried out in different tand these classifiers are; hydraulic classifiers, mechanic

cyclones. Basically they all work according to the principare suspended in water which has a slight upward moveparticles. Particles below a certain size and density are cthe water-flow, whereas the coarser and heavier particle


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Concentration The second fundamental (main) operation in mineral pr

release, or liberation, of the valuable minerals from the the separation of these values from the gangue, i.e. conce

Concentration is usually accomplished by utilizing somein physical (or chemical) properties of the metal and ganthe ore.

In concentration the following terms are used:

Head is the feed to a concentrating system.

Concentrate is defined as the valuable mineral(s) separaundergoing a specific treatment.

Tailing is the fraction of ore rejected in a separating provalueless portion, i.e. discard or waste.

Middlings are the particles of locked valuable mineral aliberation has not been attained. Further liberation can further comminution.

Recovery is the percentage of the total metal, contained recovered in the concentrate.


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Physical Concentration Meth

1. Separation dependent on optical and radioactive propi.e. hand pickling, optical sorting, radioactive sorting, et

2. Separation dependent on specific gravity (density) difi.e. heavy-media separation, gravity concentration by uscones, etc.

3. Separation utilizing the different surface properties (ichemistry) of the minerals, i.e. froth flotation, etc.

4. Separation dependent on magnetic properties of the mhigh, dry and wet magnetic separation, etc.

5. Separation dependent on electrical conductivity propeminerals, i.e. electrostatic separation, etc.


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Tyler screen scale starts with 1.05 inch (26.67 mm), for small

dimensions are usually given in microns (1 micron = 10-3 mm

(#) is equal to 74 microns in the Tyler Screen S


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Pretreatment Processes

i. Drying

ii. Calcination

iii. Roasting

iv. Agglomeration


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Pretreatment Processes

Drying

Drying usually means the removal of mechanically held water concentrate, or other solid materials by evaporation, i.e. expusually done in a drying furnace (fixed or fluidized bed, or k


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Calcination

Calcination is the thermal treatment of an ore or a concdecomposition and the elimination of a volatile product,vapor, or other gases.

Therefore, by contrast with drying, calcination involves CO2, etc., which are chemically bound as e.g. hydrates o

Temperature necessary for the

decomposition pressure to reach 1 atm

varies, e. g.

FeCO3 and Mg(OH)2 ; T 200C

MnCO3 , MgCO3 ; T 400C

CaCO3 ; T 900C

BaCO3 and Na2CO3; T 1000C


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Calcination


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Roasting

Roasting is the oxidation of metal sulfides to give medioxide.


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Temperature of Roasting

Troast > 500 - 600C: in order for the reactions to occur with sufficien

Troast < 1000C: roasting is usually carried out below the melting poi

sulfides and oxides involved and to avoid ferrite formation.Dead roast or sweet roast: Roasting to completion with the elimination

overall reaction.

Partial roasting: Removal of some of the sulfur by roasting.

e.g. partial roasting of copper concentrates

CuFeS2 + 4O2 = CuSO4 + FeSO4

2CuS + 7/2O2 = CuO.CuSO4 + SO2

Types of Roasting

1. Oxidizing roast

2. Volatilizing roast

3. Chloridizing roast

4. Sulfating roast

5. Magnetizing roast

6. Carburizing roast

7. Sinter or Blast roasting


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Agglomeration

When the particle size of an ore or concentrate is too small for u

a later stage of treatment, i.e. in the blast furnace, it must be refo

into lumps of appropriate size and strength that is agglomerated

Types of agglomeration

i. Sintering

ii. Pelletizing

iii. Briquetting

iv. Nodulizing


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Extraction via Flotatio

Froth flotation - a process where valuable minerals are separated frominducing them to gather on the surface of a froth layer. This process is based on the ability of certain chemicals to modify the surf

mineral(s).

Other chemicals are used to generate the froth and still others are used to a

The process of froth flotation involves crushing and grinding the ore t This separates the individual mineral particles from the waste rock and oth

The grinding is normally done in water with the resultant slurry called the

The pulp is processed in the flotation cells. Here the pulp is agitated with a flotation mixture

Fine bubbles are introduced

The ability of a mineral to float depends upon its surface properties. Chemical modification of these properties enables the mineral particles to

bubble.

The air bubble and mineral particles rise through the pulp to the surface of

Even though the air bubbles often break at this point, the mineral remof the froth.

The mineral is physically separated from the remaining pulp material further processing.


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Sulphide Minerals

Are sometimes roasted

Heated in air without melting to transformsulphides to oxides

Gives off H2S and SO2

Then oxides processed like Fe

Process of roasting and smelting together cre

matte

Sulfides are melted into a matte and air is

through. S is converted to sulfur dioxide

iron oxide, and Cu and Ni stay in melt Solvent extraction/electroplating

Used where rock contains Cu but in too l

amounts to be recovered by classical met


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Heap Leaching

In this process, typically done for A

ore is not ground, but rather, crushe

piled on the surface.

Weak solutions of NaCN (0.05%) pthrough the material leaching out th

desired metals.

The solutions are collected and the

are precipitated


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Cyanide extraction for

Preparation ground into fine powder

mixed in solution of NaCN (sodium cyanide) & water

referred as SLURRY

Extraction Zinc powder is added to this gold-cyanide solution which precipitates ou

The mixture then goes thru a filter where the precipitate sticks to a heavy

later cleaned to remove the gold. Extreme heat is applied which burns off the Zn

ENVIRONMENT: Gold mines make sure that cyanide doesn't escape, by using containment s

the water.

Entire operation must be kept on the alkaline side HCN is volatile and p

ALTERNATIVE PROCESSES

Gold extraction by Mercury. Elemental Hg forms an amalgam with many and gold.

Mercury boiled off, precious metals remain.

Practised in Central America 1570-1900, and in Brazil until now.


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Cyanide in the beneficiation 0.05% NaCN solution is used to extract Au and Ag from o

Au dissolves by two processes occurring simultaneously oCathode

At one end of the metal, the cathodic zone, oxygen takes uundergoes a reduction reaction.

O2 + 2 H2O + 2 e- => H2O2 + 2 OH

-

Anode

At the other end, the anodic zone, the metal gives up electran oxidation reaction.

Au => Au+ + e-

Au+ + 2CN- => Au(CN)2-

And then form strong complexes by Elsener

s/ Adamson

s

4Au + 8NaCN + O2 + 2H2O = 4NaAu(CN)2 + 4NaOH

Or Adamsons 2nd reaction

2Au + 4NaCN +2H2O = 2NaAu(CN)2 + H2O2 + 2NaOH


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Heap Leach Process


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Solvent extraction of U from


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Smelting


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Potential Environmental Pro

A. Mining operation itself

Disposal of a large amount of rock an

Noise

Dust

Beneficiation

Smelting and refining


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(8) Ore Processing (Beneficiation)