MINERAL PROCESSING for BOARD EXAMINATION

Degree of liberation

refers to the percentage of the mineral as free particles in the ore in relation to the total content. this may not be necessary at all especially when a significant characteristic difference can be utilized to separate the locked valuable mineral from the gangue.

mesh of grind

the size up to which the particles will be ground to ensure complete liberation or 80% liberation of the valuable mineral

comminution are liberation

concentration or beneficiation

two fundamental operations in mineral processing

comminution or liberation

is the whole process of reducing the raw ore to the liberation size required to effect separation of fallible minerals from the gangue

MECHANISMS:

-attrition

-impact

Rittinger's Law

the energy consumed in size reduction is proportional to the area of new surface produced

kick's law

the energy required for producing a specified reduction ratio is proportional to the log of the reduction ratio

bond's law

the law is consistent with that of griffith which states that the energy required is proportional to the length of the crack produced with energy

T=0.6 LS

T- capacity in tons per hour

L- length of crusher gape (inches)

S- with of discharge opening, set (inches)

reduction ratio formula

gyratory crusher

can be used for primary or secondary crushing. the crashing action is caused by the closing of the gap between the mantle line (movable) mounted and a central vertical spindle and the concave liner (fixed) mounted on the main frame of the crusher

GYRATORY CRUSHER HAS GREATER capacity than jaw crusher

Telsmith gyrasphere

operation of the cone crusher in which the crushing head is spherical in contour instead of a truncated cone and the crushing plate is held in position by spring under compression instead of tension as in cone crusher

gyradisc crusher

crushing is brought about by a combination of impact and attrition of multi-layered mass of particles (interparticle comminunition) brought about by the pressure due to the height of the surge capacity in the cavity and the gyrating motion of the head

hammer mills

crushes material that is friable, by impacting it against a rotating hammer ( typically traveling between 750 rpm and 1800 rpm) .

then the material is forced against a rugged solid plate called a "breaker plate" which further degrades the particle size

tumbling mills

are horizontal cylinder containing grinding media of various kinds such as rod, pebbles or steel ball are almost universally used for FINE GRINDING to secure a further comminution

abrasion and impact of the or by the promotion of unconnected media such as rods, balls and pebbles

open circuit grinding

the mill received the feed and grind to the desired product in ONE PASS

close circuit grinding

the mill discharge is fed to a sizing device to separate out the oversized material which is recycled to the grinding mill.

the recycled material is termed as circulating load and is expressed in terms of percent of new feed

open discharge

grated discharge

types of grinding mill

open discharge

the discharge of ground material is controlled by CONTROLLING THE FEED RATE

grated discharge

a grate is provided at the discharge end of the mill with openings between 0.312 to 0.937 cm and this controls the particle size in the discharge flow

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critical speed

the speed of the mill at which the load will centrifuge

65%-75%

ball mill usually operate at ---- of the critical speed

screening

refers to the size control mechanism to prevent oversized materials from being fed into grinding mills and cause choking or malfunction of the mill

usually comes in wires formed into a mesh and is positioned at an angle below the discharge point of the crusher

grizzly

25° - 50°

screen for very coarse chunks

is a series of heavy steel bars placed parallel and separated at the distance apart required for sizing

is stationary and usually set at an angle --- to the horizontal to facilitate the oversized materials sliding away once it to be size is run over

vibrating screen

30°-40°

---screens vibrating at a frequency of 1000 to 3000 vibrations per minute and installed at an angle of --- to the horizontal

the vibration prevent clogging of the screen openings by slightly oversized material that could stick in the meshes and this helps to give them a high-capacity throughput

revolving screens and trommels

are cylindrical screening surface

the feed material is fed into the interior of the screen cylinder, so that the oversized rolls on down the length of the unit, while the undersides passes out through the screen mesh opening

efficiency of screening

degree of perfection of separation of the material into size fractions above or below the governing dimensions of the aperture

ratio of the amount of material that actually passes the opening divided by the amount in the feet that should pass

capacity of a screen

is the measure of the amount of the can be screened in a given time

it is measured in tons per square foot per hour per mm of aperture

classification

method of separating mixtures of fine particles into two or more products on the basis of the velocity with which the grain fall through fluid medium

depends on their variation in size, shape and specific gravity, by allowing these particles to settle in a fluid medium ( generally water but there is also used)

WET CLASSIFICATION (where the fluid medium is water) is generally applied to mineral particles which are considered too fine to be sorted by screening

hydrocyclone

settling cones

tank classifiers

rake classifiers

spiral classifier

list of classifiers

terminal velocity

uniform rate of particle descent when equilibrium is attained between gravitational force and fluid resistance forces

SAG Mill

grinding media are ball plus rocks in the ore.

the addition of some grinding balls raises the bulk density of the grinding charge and increases throughput of the mill, as well as being more efficient than simple autogenous grinding

Sorting

separation dependent on optical and radio active properties. includes hand selection of high-grade ores.

- this is practiced in relatively few instances, but when conditions are suitable, it may prove to be a very economical process

- to be suitable for hand picking, the coarse ore must show marked segregation into high grade pieces and or large pieces of barren waste

hand picking/sorting

the ore from the course crusher is passed over a slowly moving conveyor belt or table between rows of pickers who pick off either pieces that are high grade ore or pieces that are obviously barren waste

the ore is usually sprayed with water to wash off dust and make the recognition of minerals easier

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Gravity Concentration and heavy media separation

this method takes advantage of the difference in the specific gravities of the mineral components in the ore

panning

dense media separation DMS

process jigging process

gravity concentration

jigging through the screen

jigging on the screen

types of jigs

jigging through the screen

the particles to be separated are smaller than the jigs screen. happy particles penetrate through the ragging ( a layer of course heavy particles) and scream to be drawn off as concentrated in the hutch

jigging on the screen

the particles are larger than the jig screen

both a concentrate ( bottom layer ) and the tailings (upper layer) are drawn off on the screen

direct flotation

froth product is the concentrate

reverse flotation

froth product is the tailings

outokumpu cell

we also employ a tank impeller system but the main difference is the impeller design. it consists of vertical slots tapering downwards, allowing slurry to be accelerated within the slot and expelled toward the point of maximum diameter

IONIZING COMPOUNDS dissociate in water

NON-IONIZING COMPOUNDS insoluble in water

collectors molecules may be:

conditioning

preparations done on pop prior to separation

ph regulator

dispersant

activators

depressant

modifiers

collector

reagents used to provide a water-repellent surface on the mineral to be floated so as to improve adherence of the mineral to air bubble

ph regulator

reagents used to control alkalinity

dispersants

act to break agglomerative particles apart so that single particles react with collectors and air bubbles

activators

reagents used to assess or improve the selective separation of minerals that do not respond to a simple collector-froth combination

depressants

reagents used to improve selective separation of minerals by lowering the floatability has specific minerals

ANIONIC - the non-polar group is anion

CATIONIC -the non-polar group is cation

ionizing collectors

ionizing collectors

complex molecules which are assymmetric in structure and are heteropolar consisting of nonpolar hydrocarbon group and polar group. the non-polar group under the surface to hydrophobic and the polar group reacts with water

OXYHYDRYL COLLECTORS- organic acids or soap

-carboxylate

-sulphates

-sulphonates

SULPHYDRYL COLLECTORS

-xanthates

-dithiophosphates

anionic collectors

magnetic separation

A method of separating magnetic materials from nonmagnetic ones.

can be wet or dry

electrostatic separation

this is a concentration method between minerals of different electrical properties. it is based on the phenomenon of attraction between unlike electrical charges and repulsion between like charges

this process has proved quite successful in the treatment of heavy beach sands from which the available minerals ilmenite, futile or zircon may be recovered. its application to iron ore beneficiation has also been considered

LIMITATIONS: dry method only

elutriation

a process of sizing particles by means of an upward current of fluid

A process of sizing particles by means of an upward current of fluid, usually water or air

column flotation

it is operated to maintain a net downward flow of water called POSITIVE BIAS

this feature gives SUPERIOR CLEANING ABILITYcompared with other flotation cells

Jameson Cell

uses a unique technology to separate particle contacting from the frost disengagement functions of the flotation cell

is a combination of regular flotation cell and conventional flotation cell

there is no agitator

flotation occurs almost instantaneously in the contact zone known as DOWNCOMER

Denver flotation cell

sub aerator type; most well-known cell-to-cell machine

the camping action of the impellers "suck in" slurry; making external pumps unnecessary

amount of air introduced is dependents the impeller speed

they have an agitator called IMPELLER

wemfo cell

the most widely used floatation cell

uses ROTOR-DISPERSER instead of impeller

rake classifier

spiral classifier

horizontal classifier (mechanical)

Rake classifier

mechanism of removal of course or dense material is a rake system moving up an incline

spiral or screw classifier

uses a continuous moving spiral to move sons up a slope

at the bottom

at the bottom

in jigging, the concentrate is found ---while the tailings is found ----

vertical column

flowing film concentration

categories of gravity concentration

Reichert cone

modified sluice

how it operates?

the seed is distributed evenly around the cone

the heavier particles settle the fines at the upper layer

an annular slot at the bottom accomplishes the separation

low efficiency in itself; necessitates multi-stage cones

Humphrey spirals

generally used for heavy mineral sand deposit

HELICAL CONDUIT OF MODIFIED SEMI-CIRCULAR CROSS SECTION

fluidized bed

elutriated bowls

accomplished using a perforated bowl or drum where water continuously flow, "dilating" the bed of minerals in the ring of rifles

gravitational/ static baths

centrifugal/ dynamic vessels

separating vessels- two types

gravitational or static baths

feed and medium is introduced and the floating minerals are removed by paddles or by overflow

centrifugal or dynamic vessels

provides high centrifugal force and low viscosity of medium

finer operations achieved than in static types

DESLIMING STAGE

- to prevent the media from changing its density by presence of fines

RECLAIMING CIRCUIT

for media recovery -consists of:

- vibrating drainage screens or washing sprays to recover 90% of media

- magnetic separators are flotation cells to clean media from fines

DENSIFIERS to maintain density of media

elements of Dense Media Separator DMS circuits

diamagnetic

repelled along the lines of magnetic force to a point where the field intensity is smaller

paramagnetic

attracted along the lines of magnetic force to points of greater field intensity

FILM FLOTATION

OIL BUOYANCY FLOTATION

FROTH FLOTATION

types of flotation processes