Mineral Processing: Separation Flashcards
Generally accepted as the most simple and economical of all concentration methods
* Mineral particles are separated by virtue of the differences in density - the greater the difference in density between two minerals, the more easily they can be separated
* However, the smaller the particles, the more powerful are fluid and viscous forces relative to gravity
Gravity Concentration
– typified by jigging, which takes advantage of differing rates of settlement
separation in vertical currents
- A process of sizing particles by means of an upward current of fluid
- Reverse of gravity sedimentation; Stokes’ Law applies
- Uses one or more sorting columns where the feed is separated into two fractions by their terminal velocities
- Consider a sorting column with a constant water pressure supply from the bottom, calibrated to separate minerals of separating size d
- Particles < d will move up the column; > d will report to underflow
- “enhanced decantation
Elutriation
particles are immersed in a bath containing a medium of intermediate density so that some particles float and others sink
dense-medium separation
or ‘thin film sizing‘ – shaking table or a spiral separator
separation in streaming currents
- Also known as Gold Panning and Miner’s Pan
- Used as preliminary concentration of heavy-metal ores
- Most commonly used for gold
Panning
- the minerals to be separated are stratified in a bed rendered fluid by a pulsating current below to effect stratification
- The bed “dilates”, accommodating heavier, finer particles to settle through the interstices of larger particles; larger particles experience hindered settling
Jigging
Uses the difference in magnetic properties between minerals
* Separation by applying magnetic fields:
– Magnetic valuable minerals from gangue (Fe3O4 from SiO4)
– Non-magnetic valuable mineral (SnO2 from (Fe,Mn)WO4
– Removal of tramp metals
Magnetic Separation
repelled along the lines of magnetic force to a point where the field intensity is smaller
Diamagnetic
attracted along the lines of magnetic force to points of greater field intensity
Paramagnetic
Ni, Co, Mn, Cr, Ce, Ti, O and Pt group elements also exhibit paramagnetism
* For most cases, PM of minerals is due to the presence of IRON
Ferromagnetism
high surface charge
Insulators
no charging effect
Conductors
- A method of wet concentration of ores in which separation of valuable minerals from gangue is effected by utilizing the surface-chemical properties of the minerals to enable physical separation
- Generally, separation is made possible by attaching a mineral to a bubble and letting it float above the bulk phase, leaving the other “unwanted” mineral submerged
Flotation
– The only flotation process which is of commercial importance
Froth Flotation
When air bubbles are passed through a slurry containing fine mineral particles, with certain minerals capable of attachment to the bubble
Froth Flotation
UNIQUE among applications in metallurgy, as it involves all possible interfaces:
– Air-Water (Gas-Liquid)
– Mineral-Water (Solid-Liquid)
– Air-Mineral (Gas-Solid)
Flotation
is capable of concentrating selectively and successively a number of different minerals which originally coexisted in a given ore deposit
Froth Flotation
- Is the force acting parallel to the surface of a bulk of substance, which opposes any effort to extend the interfacial area
- The natural tendency of a liquid to decrease its surface
- Denoted by γ
Surface Tension
Collection of bubbles; governed by the equation:
FROTH
maintenance of a body of bubbles at and above the upper surface of the pulp
FROTHING
Frothing Agents
* also referred to as
FROTHERS
lowers ST; the reagent concentrates at the bubble surfaces
Organic frothers
increases ST; they concentrate away from the surface
Inorganic Frothers
– does not dissociate with H2O; limited use
Non-ionizing
polar compound end dissociates with H2O; general type of collectors
Ionizing
- Have the most commercial importance
- May easily be applied to a variety of minerals by using knowledge in zeta potentials
Ionizing Collectors
- Surface-chemical reactions involves the adsorption of ions; especially free-flowing ions to a solid surface
- This occurrence is present in mineral-water couple in Flotation
Adsorption
- Time required for the disjoining film to drain such a thickness prior to rupture
- Should be less than contact time for flotation to be possible!
Induction Life
adsorption due to chemical reaction
Chemisorption
This explains the fact that solids tend to attain surface charges when introduced in water
Adsoprtion
– as a function of electrical behavior of ions
Physical Adsorption
- The essential prerequisite to separation by flotation is selective collector-coating
Conditioning
- Reagents used in flotation to control the action of a collector on minerals, in order to intensify or reduce its water repellent effect on the mineral surface
Modifiers
- Chemically altering the surface of a mineral that is exhibiting natural floatability
- Making a naturally hydrophobic mineral hydrophilic
Depression
- Essentially the semantic opposite of Depression
- Enabling a mineral that has previously no activity with a collectornto adsorb collector ions for bubble attachment
Activation
most important sa regulators
pH Modification
One of the primary objects of flotation research is to discover the optimum pH for any given combination of reagents and ore
* Most flotation plants treating sulfide ores operate with an alkaline pulp to give optimum metallurgy as well as to keep corrosion at a minimum
pH Modification
make collector action more selective with regard to minerals, thus ensuring a reasonably sharp separation from each other in flotation
Regulators
Pulp is normally held at ______ temperature
Ambient
