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Principles of Metallurgy > Mineral Processing: DEWATERING > Flashcards

Mineral Processing: DEWATERING Flashcards

1
Q
  • Solid – Liquid Separation
  • Done to produce a relatively dry
    concentrate (less shipping volume)
  • Also for certain processes that requires less or low H2O content
A

Dewatering

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2
Q

Flocculation and Coagulation

A

Sedimentation

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3
Q

Porous medium

A

Filtration

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4
Q

Evaporation of H2O content (<5%)

A

Thermal Drying

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5
Q
  • Rapid settling of solids to produce a decant-able clarified liquid
  • Governed by Stokes’ or Newton’s Laws
  • Very fine particles are either centrifuged or agglomerated
    – Flocculation
    – Coagulation
A

Sedimentation

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6
Q

– altering the stability of the suspended colloidal solids to allow them to adhere to one another

A

Coagulation

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7
Q

formation of more aggregates than coagulation by using reagent molecules acting as “bridges”

A

Flocculation

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8
Q
  • a.k.a. Thickening
  • Cheap, high-capacity
  • w/ low shear forces for flocculation
  • 2-200m diameter, 1-7m depth shallow tanks
  • provided w/ slow moving radial arms for gentle agitation and sediment collection
A

Gravity Sedimentation

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8
Q

The thickened underflow solids move continually downward to an annular trench at the center
* The clarified liquid moves upward and radially outwards
* The arms “rake” the solids @ 8m/min (perimeter)
– The arm mechanism is the basis for different thickener types!

A

Thickeners

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9
Q

The degree of thickening is a function of retention time;

A

Thickener Depth

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10
Q
  • S/L separation using porous media
  • Production of filter cake depends on:
    – Pressure difference from filter to feed
    – Area of filtering surface
    – Viscosity of filtrate
    – Resistance of filter cake
    – Resistance of filter medium
A

Filtration

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10
Q
  • Acts as support to filter cake
  • The initial layers of cake is the true filter!
  • Resistant to blinding, mechanically strong, corrosion resistant, little resistance to flow
  • Cotton, wool, linen, jute, nylon, silk, glass fiber, porous carbon, metals, rayon, porous rubber, and other synthetics
A

Filter Medium

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11
Q
  • Consists of alternately arranged plates and frames pressed by screw or hydraulic piston
  • Filter cloth is fitted in between plates
  • Slurry is fed by a continuous channel at the corners of the plates; clarified liquid is removed the same way the other end
  • Cake is washed when the filter is full, prior to discharge
A

Pressure Filters

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12
Q
  • A filter drum rotates horizontally while partially submerged in slurry
  • Suction is delivered from the inside of the drum, discharge is at the tail end of rotation
  • 0.1 – 3.0 RPM
A

Rotary Drum Filters

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13
Q
  • Similar to drum filters, but discs are used
  • The perforated discs rotate through a
    through of slurry
  • Discharge is by pulsating air blow w/ scraper
  • Small floor area vs. filtering area
A

Disc Filters

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14
Q
  • Long sloping cylindrical shell
  • Hot gases or air is fed either parallel flow or counter-current (more dry product); indirect or direct (drier)
A

Rotary Thermal Dryers

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15
Q

– Sufficient slopes w/o sharp turns; clean dry ores slide easily w/ 15- 250 steel-faced chutes
– 45-550 working slope is used; control of ore is reduced w/ increased slope

A

Chutes

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16
Q
  • 30 – 60% of total delivered price of raw materials
  • Covers the processes of:
    – Transportation
    – Storage
    – Feeding
    – Washing
    – of the ore en route to, or during its various stages of treatment in the mill
A

Ore Handling

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17
Q
  • Used when space is limited for conveyor installation
  • Continuous line of buckets attached to roller chains
  • Buckets are pivoted to remain upright until it reaches dumping position
A

Gravity Bucket Elevators

17
Q

– Most widely used for loose materials
– 20,000Mt/h; 5000m flights; 10m/s speeds
– Increased capacity by using troughing idlers
– Spacing of idlers along the belt @ maximum w/o excessive sagging
– Tensioning Devices – adjusts the belt for stretch and shrinkage to prevent undue sag

A

(Standard Rubber) Belt Conveyor

18
Q

Transport of Wet Ores

– Gently sloping troughs of rectangular, triangular, or semi-circular section
– Pulp advances by gravity; solids by either sliding or rolling
– Larger particle size, greater slope
– Deep launders for suspensions; shallow ones for fast settling solids

A

Launders

19
Q

Transport of Wet Ores

– Should be straight as possible to prevent excessive abrasion @ bends
– Oversized pipes – dangerous when encountered due to deceleration of flow; settling of solids and choking may occur
– Design is based on: S/L ratio, pulp density, solids density, particle size and geometry, fluid viscosity

A

Pipelines

20
Q

Transport of Wet Ores

– Cheap; small space requirement
– Capable of attaining high slurry velocities
– Single stage pumping may reach 30-100m heights

A

Centrifugal Pumps

21
Q

Transport of Wet Ores

Desired for delivery of uniform stream of ore
* Essentially a conveying operation;
– Shorter distance
– Close regulation of rate of ore passage
* Unnecessary for cases when succeeding operations have same rates of flow
* Consists of small bin + suitable conveyor
* Chain Feeders
– Used for smooth control of bin discharge
– Curtain of heavy loops of chain
– Chains lie on the ore @ the outfall of bin @ ≈ angle of repose
– When the loops of the chain move, the ore begins to slide

A

Ore Feeding

22
Q

Primary Crusher Feeders

– Remove fines from coarse particles before crushing
– “Scalping” the ore to prevent consolidation of fines

A

Vibrating Grizzlies

23
Q

Primary Crusher Feeders

– Long elliptical bars in alternate vertical and horizontal positions all rotating in one direction
– Rocking action sifts the ore; the fines fall through to a conveyor, the coarses tumbles across to crusher

A

Elliptical Bar Feeder

24
Q

Primary Crusher Feeders

– Essentially a conveyor w/ abrasion-resistant steel pans attached in series
– Most widely used feeder for coarse materials

A

Apron Feeders

25
Q

Removal of Harmful Materials

used when in abundance of cheap manual labor, or additional equipment installation is not economically justified

A

Hand Sorting

26
Q

Removal of Harmful Materials

situated above conveyors to pick up large pieces of tramp iron and steel; used w/ metal detectors

A

Magnetic Separators

27
Q

Removal of Harmful Materials

removal of wood from pulp (wood causes choking)

A

Vibrating Scalping Screens

28
Q

Removal of Harmful Materials

removal of slimes

A

Washing

29
Q
  • Necessity arises from successive processing units performing @ different rates
    – Intermittent vs. continuous, for repairs, and for successive batch and continuous processes
  • Depends on:
    – The equipment in the mill / method of operation
    – Frequency of maintenance work required
  • Accomplished by Stock piles, Bins, or Tanks
A

Ore Storage

30
Q
  • Can be reclaimed by front-end loaders or bucket-wheel reclaimers
  • Most economical is tunnel reclaim system
    – Conical ____ can be reclaimed by running a tunnel through the center
    – Live storage – amount of reclaimable material, is 20- 25% of total; 30-35% for elongated ______
A

Stock Piles

31
Q
  • Used as intermediate between crushing and grinding circuits
  • They allow the steady discharge of ore w/o segregation or choking
  • Flat-bottom ____ always retain some ore @ the bottom for cushioning
  • Sloping-bottom ________ for easily oxidized ore
A

Ore Bins

32
Q
  • For storing suspensions of fine solids
  • w/ provisions for agitation for suspension of solids or prerequisite chemical reactions
  • Surge tanks are also provided to control small variations in feed rate
A

Slurry Tanks / Conditioning Tanks

33
Q
  • Disposal of mill tailings causes environmental problems such as visual effect on landscape and ecological effects of water run-off
  • Depends on nature of tailings:
    – Slurries w/ high water content
    – Dewatered sludges
    – Dry coarse materials from DMS
A

Tailing Disposals

34
Q

Methods of Tailings Disposal

– application of techniques to recover additional values

A

Recycling

35
Q

Methods of Tailings Disposal

filling of mined-out areas or stopes using mill tailings

A

Back Filling

36
Q
  • Impoundment of the volume of mill tailings
  • The dam construction in itself is made of the tailings or the overburden from the mine
  • Must be constructed as cheap as possible
  • Must be constructed as close to the mine / mill as possible
A

Tailings Dam

37
Q
  • Essentially the reverse of the upstream method
  • The dam wall is raised at the opposite side of the starter dike
  • The only design acceptable by engineering standards
  • Limited by the amount of sand needed to raise the wall
A

Downstream Method

37
Q
  • A starter dam is placed @ the extreme downstream point
  • Dam wall is progressively raised on the upstream side; the tailings discharge by spigoting off the top of the starting dike
  • When the pond is filled, the dike is raised, and the cycle is repeated
  • Dam height is limited by stability of unconsolidated slimes retained by the dam walls
A

Upstream Method

38
Q
  • The crest remains in the same position as the dam wall is raised
  • Uses less sand to raise the crest to any height
  • The dam may be constructed ahead of the tailings pond
A

Center-line-method

39
Q

to neutralize acids and precipitate
heavy metals as insoluble hydroxides
* Removal of decanted surplus water from dam
– may be recycled to plant upon treatment

A

Lime

39
Q
  • Impervious foundations and interception ditches
    – to prevent seepage to groundwater
A

Mitigating Techniques

40
Q

waste water treatments

– neutralization /
precipitation

A

Chemical stabilization

41
Q

waste water treatments

ctive carbon and
clays

A

physical absorption

42
Q

waste water treatments

– micro-algae species

A

Biological Oxidation

Principles of Metallurgy (13 decks)

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