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Unit Operations in Mineral Processing

front 1 COMMINUTION	back 1 Size reduction by particle breakage ▪ liberation • Create particles in certain size and shape • Increase surface area available for next process
front 2 Comminution usually accounts for more than ____ total power	back 2 40 % to 50%
front 3 Only about ____ of the energy input is used to comminute	back 3 3% – 5 %
front 4 Problems associated with comminution:	back 4 ➢ It is mechanically a wasteful process. ➢ Most of the energy input is lost to a lot of factors. ▪ Absorbed by the equipment ▪ Water resistance in pulp ▪ Deformation (not breakage) of plastic particles ➢ Heat is unavoidably produced.

front 5	back 5 An empirical relationship between energy consumed during size reduction and particle size.
front 6 Rittinger’s Law	back 6 energy of breakage ∝ amount of new surfaces produced
front 7 Kick’s Law	back 7 energy required ∝ reduction in volume of the particles concerned
front 8 Bond’s Law	back 8 energy required ∝ new crack tip length produced in particle breakage

front 9 Work Index	back 9 Energy required to reduce one ton of ore from a very large size to 100µm
front 10 Jaw Crusher	back 10 1) Blake 2) Dodge Type
front 11 BlakeS	back 11 Movable jaw is pivoted at the top
front 12 Dodge Type	back 12 Movable jaw is fixed at the bottom

front 13 Relative motion of the crushing faces is due to gyration motion of an eccentrically mounted cone	back 13 gyratory crusher
front 14 Comminution by impact; sharp blows on free-falling rock	back 14 IMPACTORS
front 15 Modified gyratory crusher that yields smaller product	back 15 CONE CRUSHERS
front 16 Consists of two horizontal cylinders revolving towards each other	back 16 ROLL CRUSHERS

front 17 GRINDING	back 17 Last stage in comminution process
front 18 Grinding Size Reduction	back 18 impact + abrasion
front 19 What is used when grinding medium is present	back 19 balls or rods
front 20 Green • Parabolic path taken by charge as projected by lifting of the mill • Coarse grinding by impact	back 20 Cataracting

front 21 Black • Rolling motion of the charge down to the toe • Leads to finer grinding by abrasion	back 21 Cascading
front 22 Red Charge is carried around in a fixed position	back 22 Centrifuging
front 23 Uses cast iron rods as grinding medium	back 23 Rod Mill
front 24 Uses forged steel balls as grinding medium	back 24 Ball Mill

front 25 The action of the ore grinding upon itself with small amount of ball charge	back 25 Semi-autogenous Mill
front 26 SIZING	back 26 Selection of materials based on their size
front 27 SCREENING (Industrial Screening)	back 27 Use of screening equipment (screens) • Extensively used for size separations from 300 mm down to roughly 40 µm, efficiency decreases rapidly with fineness
front 28 Screen equipment are classified as	back 28 stationary and moving

front 29 SCREENING objectives	back 29 To optimize the feed of the comminution stage by preventing the materials which are already smaller, not to enter this stage • To ensure that the desired product is according to the size application • To ensure that the feed to succeeding process does not exceed size limitation of receiving area
front 30 Sizing/Classifying	back 30 To separate particles by size
front 31 Scalping	back 31 To remove coarsest size fractions in the feed material
front 32 Grading	back 32 To prepare a number of products within specified size ranges

front 33 Media recovery	back 33 For washing magnetic media from ore in dense medium circuits; or to retain grinding media inside grinding mills
front 34 Dewatering	back 34 To drain free moisture from a wet sand slurry
front 35 De-sliming/De-dusting	back 35 To remove fine material, generally below 0.5 mm, from a wet or dry feed
front 36 Trash removal	back 36 Usually to remove coarse wood fibers or tramp material from a slurry stream

front 37 Static Grizzlies	back 37 • 35 – 50° deck angle • Uses heavy parallel bars • Used with coarse crushing (scalping operations)
front 38 Sieve Bends	back 38 • >50μm, 180m3/hr • Curved screen w/ horizontal wedge bars • Slurry enters tangentially to the bend • Peeling action of the slurry bed
front 39 stationary screens	back 39 1. Static Grizzlies 2. Sieve Bends
front 40 moving screens	back 40 Grizzly Screens Trommels

front 41 Grizzly Screens	back 41 • Usually screens very coarse material • Characterized by parallel steel bars on rails set at a fixed distance apart and installed in line with the flow of ore
front 42 Trommels	back 42 • Comprised of a cylindrical screen • Can be made to deliver sized products by using a series from finest to coarsest or using concentric trommels with the coarsest mesh being innermost
front 43 CLASSIFICATION	back 43 LESS Than 1mm Method of separating mixtures of minerals into 2 or more products based on the velocity of the particles as the grains fall through a fluid medium (liquid or gas)
front 44 Wet classification	back 44 usually uses water, generally applied to mineral particles considered too fine to be sorted efficiently by screening

front 45 CLASSIFIERS	back 45 • used for particles 1mm or less
front 46 CLASSIFIERS categorized by force field applied to unit	back 46 either gravitational or centrifugal
front 47 Hydrocyclone	back 47 Utilizes centrifugal force to accelerate settling rate of particless
front 48 gravitational classifiers	back 48 Spiral Classifier Rake Classifier

front 49 Spiral Classifier	back 49 A continuously revolving spiral moves the sands up the slope
front 50 Rake Classifier	back 50 Uses rakes actuated by an eccentric motion, which causes them to dip into the settled material and move up the incline for a short distance
front 51 GRAVITY CONCENTRATION	back 51 • Most simple and economical of all concentration methods • Particles are separated by their differences in density • Greater density difference = easier separation
front 52 Dense Media Separation	back 52 Particles are placed in a liquid of known density. Denser particles sink while lighter particles float

front 53 Vertical Current Separation	back 53 Stratification of mineral layers based on their densities on a particle bed, fluidized by a stream of water
front 54	back 54 Jigging
front 55	back 55 Shaking Table
front 56 Separation via altering surface-chemical properties of minerals bubbles	back 56 FROTH FLOTATION

front 57 • Uses the difference in magnetic properties between minerals	back 57 Magnetic Separation
front 58 Uses the difference in electrical conductivities between minerals	back 58 High Tension Separation
front 59 DEWATERING	back 59 Solid – Liquid Separation • Produces a relatively dry concentrate (less shipping volume) • For certain processes that requires low H2O content
front 60 Dewatering (combination of the three)	back 60 Sedimentation Filtration Thermal Drying

front 61 Sedimentation	back 61 Increases concentration of suspensions by settling solids
front 62 Filtration	back 62 Uses a porous medium that blocks solids (filter cake) and allows liquids (filtrate) to pass through.
front 63 Thermal Drying	back 63 Final operation in a mineral processing plant. Moisture content is lowered to ~5 wt%
front 64 Sedimentation	back 64 Coagulation Flocculation

front 65 Coagulation	back 65 Neutralizes charged particles so that they will settle and not continuously repel each other
front 66 Flocculation	back 66 Uses long-chain polymers to bridge particles until they areheavy enough to settle
front 67	back 67 THERMAL DRYING \| rotary dryer
front 68 ORE HANDLING	back 68 Costs account for 30 – 60% of total delivered price of raw materials • Covers the processes of transportation, storage, feeding, washing, and sampling of the ore en route to, or during its various stages of treatment in the mill

front 69 ORE TRANSPORTATION	back 69 Minimum upward and horizontal movement • Maximum practicable pulp density
front 70 ORE TRANSPORTATION (Basic Philosophy)	back 70 • The use of gravity should be maximized. • There should be continuous movement. • Shortest possible distances in between processing units should be utilized.
front 71 ORE TRANSPORTATION \| dry ore	back 71 Chutes (Standard Rubber) Belt Conveyor Gravity Bucket Elevators
front 72	back 72 Chutes

front 73	back 73 (Standard Rubber) Belt Conveyor
front 74	back 74 Gravity Bucket Elevators
front 75 ORE STORAGE	back 75 Necessity arises from successive processing units performing at different rates ▪ Intermittent vs. continuous, for repairs, and for successive batch and continuous processes
front 76 ORE STORAGE Depends on	back 76 ▪ The equipment in the mill / method of operation ▪ Frequency of maintenance work required

front 77 ORE STORAGE Accomplished by having	back 77 stockpiles, and using bins or tanks
front 78 ORE STORAGE	back 78 Stockpiles Ore Bins Slurry Tanks / Conditioning Tanks
front 79 Can be reclaimed by front-end loaders or bucket-wheel reclaimers	back 79 Stockpiles
front 80 • Used as intermediate between crushing and grinding circuits • They allow the steady discharge of ore w/o segregation or choking • Sloping-bottom bins for easily oxidized ore	back 80 Ore Bins

front 81 • For storing suspensions of fine solids with provisions for agitation for suspension of solids or prerequisite chemical reactions	back 81 Slurry Tanks/Conditioning Tanks
front 82 ORE FEEDING	back 82 Desired for delivery of uniform stream of ore • Unnecessary for cases when succeeding operations have same rates of flow
front 83 • Used for smooth control of bin discharge • Consist of curtain of heavy loops of chain which when moves, the ore begins to slide	back 83 A. Chain Feeders
front 84 • Essentially a conveyor with abrasion-resistant steel pans attached in series • Most widely used feeder for coarse materials	back 84 B. Apron Feeders

front 85 • Remove fines from coarse particles before crushing • “Scalping” the ore to prevent consolidation of fines	back 85 C. Vibrating Grizzlies
front 86 • 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 coarsest tumbles across to crushe	back 86 D. Elliptical Bar Feeder
front 87 Hand Sorting	back 87 used when in abundance of cheap manual labor, or additional equipment installation is not economically justified
front 88 Magnetic Separators	back 88 situated above conveyors to pick up large pieces of tramp iron and steel; used w/ metal detectors

front 89 Vibrating Scalping Screens	back 89 removal of wood from pulp (wood causes choking)
front 90 Washing	back 90 ▪ removal of slimes (very fine particles) • Uses high-pressure water jets over vibrating screens
front 91 Measures of Efficiency	back 91 DEGREE OF LIBERATION MESH-OF-GRIND PARTICLE SIZE ANALYSIS
front 92 DEGREE OF LIBERATION	back 92 The percentage of a mineral or phase occurring as free particles in relation to the total of the minerals in the ore

front 93 MESH-OF-GRIND	back 93 The size up to which the ore is ground to ensure sufficient liberation of wanted mineral • Normally taken as 80% passing product • Balance between liberation and economics (longer grinding duration = higher costs)
front 94 PARTICLE SIZE ANALYSIS	back 94 Control of quality of grinding • Measure of degree of liberation • Determining the optimum feed size • Establishing the grinding limit to reduce losses