Fundamentals of Flotation

Fundamentals of

Froth Flotation

Fuel and Mineral Engineering DepartmentIndian School Of Mines, Dhanbad.

Authors:Himesh Patel Aditya Kumar

What is froth flotation?Froth flotation, is a physicochemical method of concentrating fine minerals and coal.

It can be stated that Flotation is a physiochemical separation process that utilises the difference in surface properties of the valuable minerals and the gangue minerals.

E.g.

Removing silicate minerals from iron ores.

Principle of Froth FlotationFlotation is a physiochemical separation process that utilises the difference in surface properties of the valuable minerals and the unwanted gangue minerals.

The material recovery process by flotation comprises three mechanisms:

Selective attachment to air bubbles

Entrainment in the water which passes through the froth.

Physical entrapment between particles in the froth attached to air bubbles

Ways of Flotation1. Direct Flotation: In which the mineral is attached to the froth

and the gangue remains in the tailings.

E.g. Hematite flotation

2. Reverse Flotation: In which the gangue is attached to the froth and minerals remain in tailing.

E.g. Quartz flotation

Mechanics of FlotationThe basis of Froth Flotation is the difference in the WETTABILITY of the mineral and gangue particles.

On the basis of Wettability of particles are classified as HYDROPHOBIC and HYDROPHILIC.

The valuable minerals can attach to the air bubbles , only if they are Hydrophobic. Once they reach the surface, due to the buoyancy of the air bubbles, the particle-bubble contact can sustain only if they form a stable froth.

The stability of the froth depends on the strength of the attachment of the bubble to the mineral surface. This strength can be estimated with the help of YOUNG-DUPRE EQUATION, which relates the strength of attachment to the interfacial energies.

WHERE, in the above equation, ΓW/A, ΓS/A, ΓS/W are the SURFACE ENERGIES between water-air, solid-air, solid-water interface and θ is the CONTACT ANGLE.

Flotation SystemChemistry Components :Collectors, Frothers, Activators, Depressants, pH Control.

Equipment Components:Cell Design, Agitation, Air Flow, Cell Bank Configuration, Cell Bank Control.

Operation Components:Feed Rate, Mineralogy, Particle Size, Pulp Density, Temperature.

Chemistry Components1. A collector is a chemical that attaches to the mineral surface and

produces a hydrophobic (water-fearing) surface. E.g. oils, xanthates, fatty amines

2. Frothers are liquids that produce the froth or foam on which the flotation process depends. E.g. pine oil, MIBC (Methyl Isobutyl Carbinol)

3. Activators are specific compounds that make it possible for collectors to adsorb onto surfaces that they could not normally attach to.E.g. copper, ZnS(s) + Xanthate-

4. Depressants have the opposite effect of activators, by preventing collectors from adsorbing onto particular mineral surfaces. E.g. Cyanides, Limes, Organic Depressants

5. pH CONTROL: The surface chemistry of most minerals is affected by the pH.

Flotation tank cell

Jameson Cell

Flocculation Flocculation involves the formation of much more open

agglomerates than those resulting from coagulation and relies upon molecules of reagent acting as bridges between separate suspended particles.

Selective flocculation of the desired minerals in the pulp, followed by separation of the aggregates from the dispersed material, is a potentially important technique, although plant applications are at present rare.

Present Challenges

•Particle size and density

•Pulp density

•Air bubble size

•Agitation intensity

•Conditioning time•Residence time

•Nature of Particle (Particle surface charge)

•pH of slurry

•Type of reagent

•Amount of reagents

•Frother stability

Flotation In CoalFroth flotation is the most commonly used process to recover and upgrade the portion of the coal preparation plant feed that has a particle size smaller than 150 microns. Problems that occur when employing froth flotation in the coal industry include

i) Coal surfaces that are weakly-to-moderately hydrophobic, and

ii) flotation systems that are overloaded and limited by insufficient retention time.

Flowsheet

Reference• Wills, B.A. and Napier-Munn Tim, “Mineral Processing

Technology”, Elsevier(2005)

• Kavatra, S.K., “Flotation Fundamentals”

• Ray, H.S. and Sridhar, R., “Extraction of Non- Ferrous Metals”

• Saracoglu, Mehmet, "FROTH FLOTATION PERFORMANCE ENHANCEMENT BY FEED CAVITATION AND MAGNETIC PLASTIC PARTICLE ADDITION" (2013). Theses and Dissertations--Mining Engineering. Paper 9.http://uknowledge.uky.edu/mng_etds/9

• www.imn.gliwice.pl/public/doc/maszyny-flotacyjne_en.pdf

• http://www.metso.com/miningandconstruction/mm_sepa.nsf/WebWID/WTB-041102-2256F-C598E?OpenDocument#.UzNPOvmSwRo