Dr.
Leonardo C. Medina Jr.
8th Edition
7th Edition Section 19 Pages 19-56 to 19-65
it includes any operation in which one solid is separated from another by floating one of them on the surface of the fluid.
Schematic Diagram of a Dissolved Air Flotation Equipment
Schematic Diagram of an Electrolytic Flotation Equipment
Unit Operation of Flotation is based on two major steps: 1. Conditioning 2. Separation The main purpose of the conditioning step is to create physical-chemical conditions for achieving appropriate selectivity between particle species that are to be separated. The second step is then intended to generate and introduce air bubbles into the process vessel for contacting them with particulate species so as to affect their separation by flotation.
Basic Steps in a Flotation System Particles attached to the air bubbles are in most applications removed from the process vessel as froth. Froth overflow concentrate
Feed
Conditioning
Reagents
Separation
Reagents
Tailings underflow
Air
The unit operation of flotation is often referred to as f r o t h f l o t a t i o n . The froth overflow stream is called a c o n c e n t r a t e in the minerals industry, and the slurry underflow is termed tailings.
Schematic Diagram of a Flotation Column
It involves chemical treatment of the ore pulp to create conditions favorable for the attachment of certain mineral particles to the air bubbles. The air bubbles carry the selected minerals on the surface of the pulp which is skimmed off while the other minerals submerged at the bottom.
Schematic Diagram of Mechanical Flotation Cell
Denver Flotation Machine
Agitair Flotation Machine
Fagergren Flotation Machine
Flotation Reagent
Feed,
F
Water
Concentrate,
FLOTATION
XC
XF
Tailings,
T
XT
F=C+T XFF =XCC + XTT
Dry Basis
C
Flotation Reagents Three types of chemical reagents are used during the froth flotation process: 1. collectors 2. frothers 3. modifiers 3.1. Activators 3.2. pH Regulators 3.3. Depressants 3.4. Dispersants and Flocculants
1. Collectors or Promoters – alter the surface of the mineral in order that it will become air-avid (to cause it to adhere to air bubbles) Examples: a. xanthates; dithiophosphates - for flotation of metallic sulfides and native metals. b. crude or refined fatty acids and their soaps; petroleum; sulfonates; sulfonated fatty acids - for flotation of fluorspar, phosphate rock, iron ore and other non metallics. c. fatty amines; amine salts - for flotation of quartz, potash and silicate minerals
2 . Fr o t her s – added to strengthen temporarily
covering film of the air bubbles. It serves to stabilize the froth and holds the minerals until the froth can be scraped off into the concentrate launder. Commonly used frothers: a. pine oil c. polypropylene glycol ether b. cresylic acid d. 5 to 8 carbon aliphatic alcohols
Examples: methyl isobutyl carbinol and methyl amyl alcohol
3 . Mo d i f i er s Flotation modifiers include several classes of chemicals.
3 . 1 . Act i v a t or s - These are used to make a
mineral surface amenable to collector coating. Copper ion is used, for example, to activate sphalerite (ZnS), rendering the sphalerite surface capable of absorbing a xanthate or dithiophosphate collector. Sodium sulfide is used to coat oxidized copper and lead minerals so that they can be floated by a sulfide mineral collector. 3.2. p H r egul a t o r s - Regulators such as lime, caustic soda, soda ash, and sulfuric acid are used to control or adjust pH, a very critical factor in many flotation separations.
3. 3. Depr essant s - Depressants assist in selectivity
(sharpness of separation) or stop unwanted minerals from floating. Typical are sodium or calcium cyanide to depress pyrite (Fe2S2) while floating galena (PbS), sphalerite (ZnS), or copper sulfides; zinc sulfate to depress ZnS while floating PbS; sodium ferrocyanide to depress copper sulfides while floating molybdenite (MoS2); lime to depress pyrite; sodium silicate to depress quartz; quebracho to depress calcite (CaCO3) during fluorite (CaF2) flotation; and lignin sulfonates and dextrins to depress graphite and talc during sulfide flotation.
3.4. Dispersants and flocculants - These are important for the control of slimes that sometimes interfere with the selectivity and increase reagent consumption. For example, soda ash, lime sodium silicate, and lignin sulfonates are used as dispersants, and starch and polyacrylamide are used as flocculants. Quantities of modifying agents used vary widely, ranging from as little as 0.01 to 0.1 g/kg to as high as 1 to 2 g/kg of solids, depending upon the reagent and the metallurgical problem.
Analysis: By material balance on each unit DATA: 1. density of minerals 2. L/S, water to solid ratio 3. composition of feed, concentrate and tailings 4. reagents 5. contact time 6. type of flotation cells
The schematic diagram showing the relationship between the physical and chemical properties of fine particles and their behavior in flotation. (G) and (R) refer to whether the phenomena affects grade and/or recovery. The arrows indicate the various factors contributing to a particular phenomena observed in flotation of fine particles
