Basics in Minerals Pro Processing cessing
CONTENT Introduction
1
Minerals in operation
2
Size reduction
3
Crushing Grinding
Size control
Screening Classification
Enrichment
6
Sedimentation Mechanical dewatering Thermal drying Thermal processing
Materials handling
5
Washing Gravity separation Flotation Magnetic separation Leaching
Upgrading
4
7
Unloading Storing Feeding Conveying
Slurry handling
8
Slurry transportation Agitation and mixing
Wear in operation
9
Operation and environment
10
Process systems
11
Miscellaneous
12
BASICS IN MINERAL PROCESSING
BASICS IN MINERAL PROCESSING
Enrichment
Separation by jigs* The jig operation consists of two actions. One is the effect of hindered settling meaning that a heavier particle will settle faster than a light particle. The other one is the separation process in an upward flow of water which will separate the particles by their density. These two actions are combined in a Jig by slurry pulses generated mechanically or by air.
Separation by spiral concentrators* A spiral concentrator uses gravity to separate particles of different densities. It should not be confused with a spiral classifier which usually separates particles of different size, see section 4. A spiral concentrator consists of one or more helical profiled troughs supported on a central column. As slurry travels down the spiral high and low density particles are stratified and separated with adjustable splitters at the end of the spiral.
Separation by shaking tables* A cross stream of water transports material over the table to riffles running perpendicular to the direction of feed. Particles build up behind each riffle and stratification occurs with heavier particles sinking to the bottom. The light particles are carried over each riffle to the tailings zone. The shaking action of the tables carries the heavy particles along the back of each riffle to the concentrate discharge.
Heavy Light
Water feed
Slurry feed
Tailings
Concentrate
Middlings
*Not available from Metso
BASICS IN MINERAL PROCESSING
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t n e m h c i r n E
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Sizing 4
3
) s d i l o s ( r h / n o t
2
1
0 0
t n e m h c i r n E
2 (23)
4 (46)
6 (65)
8 (86)
Deck area m2 (ft2)
Separation in dense media Gravity separation utilizes the settling rate of different particles in water to make a separation. Particle size, shape and density all affect the efficiency of the separation. Dense Media Separation (DMS) takes place in fluid media with a density between that of the light and heavy fractions that are to be separated. The separation is dependent upon density only
DMS – fluid media Media Sand in water Fine (- 50 micron or 270 mesh) Magnetite in water Atomized Ferrosilicon in water “Heavy Liquids” for lab testing
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Density 1.2 – 1.6 1.6 – 2.5 2.4 – 3.5 1.5 – 3.5
BASICS IN MINERAL PROCESSING
Enrichment
Separation by flotation Flotation is a mineral separation process, which takes place in a water-mineral slurry. The surfaces of selected minerals are made hydrophobic (water-repellent) by conditioning with selective reagents. The hydrophobic particles become attached to air bubbles that are introduced into the pulp and are carried to a froth layer above the slurry thereby being separated from the hydrophilic (wetted) particles.
Air bubble Hydrophobic reagents
Air bubble
Particle t n e m h c i r n E
Particle surface
In addition to the reagents added, the flotation process depends on two main parameters. •
Retention time needed for the separation process to occur determines the volume and number of flotation cells required.
•
Agitation and aeration needed for optimum flotation conditions, determine the type of flotation mechanism and the power input required.
Size of cells – lengths of banks As flotation is based on retention time we have two alternative approaches: • •
Small cells and longer banks Fewer large cells and shorter banks
The first alternative is a more conservative approach and is applicable to small and medium tonnage operations. Using more smaller cells in flotation means • • •
Reduced short circuiting Better metallurgical control Higher recovery
The second alternative is becoming more accepted for high tonnage operations using large unit volume flotation machines. Modern flotation equipment gives opportunities to use larger cells and shorter circuits. • • • • •
Effective flow pattern minimizes shortcircuiting Improved on line analyzers will maintain good metallurgical control Less mechanical maintenance Less energy input per volume pulp Lower total cost
Selection of cell size is made on the basis of the largest individual cell volume that will give the required total flotation volume with an acceptable number of cells per bank. Typical figures for different minerals are given later in this section. BASICS IN MINERAL PROCESSING
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Flotation circuit layout Flotation circuit designs vary in complexity depending primarily on the type of mineral, degree of liberation of valuable minerals, grade (purity) of the product and the value of the product.
Simple circuit (e.g. coal) Single stage flotation, with no cleaning of the froth. Feed Feed
WWaste ast
Product Product
Commonly used circuit (e.g. lead) t n e m h c i r n E
Single stage rougher, two stages of cleaning, no regrind. WWaste ast
Feed Feed
Product Product
Complex circuit (e.g. copper) Two stages roughing (a,b), one stage scavenging (c), three stages cleaning (d), cleaner scavenger (e), regrind. Feed Feed
a
c
b
W aste Waste
d
d
Middlings Middling d
e
to (a)(a) after afte to regrinding regrinding
Product Product
Typically the first rougher stage would comprise 10 – 40 % of the total rougher volume and will produce a good grade concentrate with but only medium recovery. The second rougher stage comprises 60 – 90 % of the total rougher volume and is designed to maximize recovery. The scavenger cells would have a cell volume equal to the total rougher stage and are included when particularly valuable minerals are being treated or a very high recovery is needed. Cleaner cells are used to maximize the grade of the final concentrate. Typical cleaner retention time is 65 – 75% of that for rougher flotation and will be at a lower percent solids. Less cells per bank than for rougher duties can be used. 5:8
BASICS IN MINERAL PROCESSING
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Reactor cell flotation system (RCS) The RCSTM (Reactor Cell System) flotation machine utilizes the patent protected DV TM (Deep Vane) Mechanism. Flow pattern characteristics are: • Powerful radial slurry ow patterns to tank wall (1). • Primary return ow to
underside of impeller (2). • Secondary top recirculation
3
3
1
1
2
2
(3). Flotation enhanced due to: • Maximum particle-bubble
contacts within the mechanism and tank. • Eective solids suspension
during operation and re-suspension after shutdown.
t n e m h c i r n E
• Eective air dispersion throughout the complete cell volume.
Features of the RCSTM (Reactor Cell System): •
Active lower zone for optimum solid suspension and particle – bubble contact.
•
Upper zone with reduced turbulence to prevent particle – bubble separation.
•
Quiescent cell surface to minimize particle re-entrainment.
•
Circular tank with low level slurry entry and exit to minimize slurry short circuiting.
•
Cell size 0.8 – 300 m3 (28 – 10600 ft3)
•
V-V drive up to 70 m3. Gearbox drive for 100 m 3 and above. (V-V drive for larger
volume cells optional) •
Automatic level control by dart valves.
•
Separate source of low pressure air.
•
Double internal cross-ow froth launders or internal peripheral launders with
central crowder. •
Application: The majority of mineral otation duties.
See data sheet 5:14. BASICS IN MINERAL PROCESSING
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Enrichment
Reactor cell system (RCS) – Sizing, metric Selection of the size and number of cells for each stage of the flotation circuit (roughing, cleaning etc) is made by a three step calculation.
1. Determination of total flotation cell volume Total flotation cell volume required can be calculated from the formula: Vf = Q x Tr x S 60 x Ca Vf = Total flotation volume required (m3) Q = Feed flow rate m3/hr Tr = Flotation retention time (minutes). Typical figures for different minerals are given overleaf, alternatively the retention time may be specified by the customer or be determined from testwork. t n e m h c i r n E
S
= Scale up factor dependent upon source of flotation retention time date (above) Tr specified by customer S = 1.0 Tr taken from typical industrial data S = 1.0 Tr taken from continuous Pilot Plant test S = 1.0 Tr taken from laboratory scale test work S = 1.6 – 2.6
Ca = Aeration factor to account for air in pulp. 0,85 unless otherwise specified.
2. Select the number of cells per bank The table overleaf shows typical amount of cells per bank for common mineral flotation duties. Divide Vf calculated above by number of cells selected to calculate volume (m3) per cell. Check that Q is in ow rate range for cell size selected. Reselect if necessary.
3. Select the bank arrangement To ensure necessary hydraulic head to allow slurry to flow along the bank intermediate boxes may be required. Maximum numbers of cells in a section between intermediate or discharge boxes are given overleaf. Each bank will also
need a feed box and a discharge box. Typical bank designation is F-4-I-3-D, i.e. Feed box, four cells, intermediate box, three cells, discharge box.
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BASICS IN MINERAL PROCESSING
Slurry pumps – range VT _______________________________________________8:21 Technical data: VT _____________________________________________________ 8:22 Slurry pumps – range VF _______________________________________________ 8:23 Technical data: VF _____________________________________________________ 8:24 Application guide for slurry pumps _______________________________________8:25 Selection – by solids ___________________________________________________8:26 Selection – by head and volume ________________________________________ 8:26 Selection – by slurry type _______________________________________________8:27 Selection – by industrial application ______________________________________8:28 Minerals ____________________________________________________________8:28 Construction _________________________________________________________8:29 Coal ________________________________________________________________8:29 Waste and recycling ___________________________________________________8:30 Power and FGD _______________________________________________________8:30 Pulp and paper _______________________________________________________8:30 Metallurgy ___________________________________________________________8:31 Chemical ____________________________________________________________8:31 Mining ______________________________________________________________8:32 Agitation – Attrition scrubber ___________________________________________8:33 Attrition scrubber – Sizing _____________________________________________ 8:33 “The slurry line” _______________________________________________________8:34 Slurry handling hoses __________________________________________________8:34 Technical data: Material handling hoses ___________________________________ 8:37 Technical data: Rubber lined steel pipes ___________________________________ 8:37 Technical data: 3xD bends 45o ___________________________________________8:38 Technical data: 3xD bends 90o ___________________________________________8:38 Technical data: Branch pipes ____________________________________________ 8:39 Technical data: Gaskets ________________________________________________ 8:40 Technical data: Couplings ______________________________________________ 8:41 Technical data: Reducers, rubber lined steel ________________________________ 8:42 Technical data: Compensators ___________________________________________ 8:43 Technical data: Tailing compensators / bends ______________________________ 8:43 Technical data: Tailing pipes ____________________________________________ 8:44
BASICS IN MINERAL PROCESSING
