Collectors of Froth Flotation

Froth flotation is a concentration method for separating materials based on their density and affinity for water. It’s mostly used to remove the gangue particle from the desired particles. Different flotation chemicals have different physico-chemical characteristics. The separation of minerals by froth flotation works on the properties of these reagents. The collectors in froth flotation reagents adsorb to the surface of desired minerals and form a hydrophobic layer. This layer separates the minerals from the gangue. The froth flotation has a wide range of practical applications- Mineral separation, plastic separation, sewage water treatment, and paper recycling are just a few of the applications for froth flotation. Mineral processing and the maximum separation capacity are two advantages of froth flotation. It also has drawbacks, such as significant costs and maintenance.

Froth flotation

Froth flotation is a concentration process that selectively separates minerals based on their relation with water and their density. It is widely accepted over other separation methods like magnetic separation and gravity separation. The froth flotation method is dependent on the flotation reagents, not on the properties of minerals.

Froth flotation process

Ore is treated through processes like roughing, cleaning and scavenging to obtain the most concentrated form of the desired mineral without impurities.

• By a process called ‘liberation’, an ore is separated into various minerals.
• Provide a hydrophobic environment for desired minerals using chemicals or surfactants by ‘conditioning’
• A sludge form of minerals with water and the frothing agent is added to the flotation column.
• Frothing takes place with the incorporation of air and only desired minerals or metal levitate to surface with air bubbles- ‘Frothing’
• Separate the froth with a maximum concentration of the desired mineral- ‘separation’

List of chemicals used

For the process of froth flotation, we use various reagents. Most of them are in liquid form. If that is in dry form, it must feed dry. We use one pound of reagent for one ton of ore/minute normally.

Collectors

We have to make our desired mineral hydrophobic to get it bound to air bubbles. Collectors act as a base for making minerals hydrophobic. It increases their floating capacity making them easy to separate.

Examples: Xanthates, thiourea thiocarbanilide and fatty acid.

Activators 

As the name suggests, activators encourage the binding between collector and desired mineral.

Example: Copper sulphate

Frothers

Frothers are foam creating reagents, which produce a  small air bubble to which desired mineral is attached. Frothers reduce the surface tension of water.

Example: pine oil, cresylic acid and poly glycol.

Modifiers

Interaction between mineral and collector should take place to run the froth flotation. Modifiers change the characteristics of a mineral and insist it attaches with the collector.

Example: lime and soda ash (pH modifier), phosphates and silicates (anionic modifier), Starch and dextrin (cationic modifier).

Depressants

These are the reagents used to depress the flotation of certain minerals other than the desired one. This one is acting like an inhibitor.

Example: Dichromate, Sodium cyanide. 

Collectors

Collectors are the floatation reagents used to form a thin hydrophobic layer over desired minerals. This hydrophobic layer decreases the wetting of minerals, increasing the separation of gangue particles (wetted in water) from the minerals. Collectors can bond to the mineral surface by chemisorptions or physical absorption.

The collectors are considered to be more important in the separation of iron ores. The function of the collector reagent is to promote affinity between mineral particles and air bubbles by  forming a hydrophobic coating on the surface of the mineral particle. 

Collectors can be anionic, cationic and non ionic Fatty acids, xanthates, pine oils etc are the common collectors used in froth flotation.

Collector’s examples

Collectors can be anionic, cationic and non-ionic.

Cationic – Cationic collectors enhance the mineral’s surface chemistry. These are bonded to minerals by electrostatic force. Due to this electrostatic force of attraction, cationic collectors are found to have low adhesive capacity. They produce positively charged hydrocarbon-bearing ions

Example: Fatty amines

Anionic – They are mainly used for the collections of alkaline earth metals and alkali minerals. Anionic collector groups mainly include carboxylates, oleic acid…

Example: Low-grade coal particles have a little contact angle, which makes them difficult to float in separation. When a carboxylic acid is added as a collector, it is found to be enhancing the floating capacity of coal. 

Non-ionic- These are oils of basic hydrocarbons mainly- pine oil, kerosene…

Example: When we separated low-grade coals with non-ionic collectors (mixture of kerosene and pine oil), there was a considerable amount of ash concentrated with it. When we used ionic collectors like fatty acids, there was a significant reduction in the concentration of ash.

Some common collectors and their mode of addition

Fatty acids

Fatty acids are collectors for iron ores, precipitated by hard water.

1. Oleic acid – added to the mineral pulp as a liquid emulsion
2. Refined oleic acid- added to the mineral pulp as a liquid emulsion
3. Na soap of fatty acids –  added  to the mineral pulp as 5 to 20% solution

Alkyl sulphates and sulfonates

Alkyl sulphates and sulfonates are also collectors for iron ores.

1. Dodecyl to cetyl – added to the mineral pulp as 5 to 20 % solution. It is used to float SiO2
2. Amine acetates – 5-10% solution. It is used to float quartz, silicates
3. Quaternary ammonium salts – 5-10% solution. It is used to float quartz, silicates
4. Ether amines and diamines – Undiluted. It is used to float quartz, silicates

Anionic sulphur ligands

 They are mainly xanthates- Potassium amyl xanthate, Sodium isobutyl xanthate and Potassium ethyl xanthate. It is used in the flotation of Cu, Mo and Ni.

Conclusion

Froth flotation separates minerals from the gangue particles based on their surface chemistry. This process uses the characteristics of froth flotation chemicals to float certain minerals. In short, the froth flotation method depends on the flotation reagents, not on the properties of minerals.

Collectors form a thin hydrophobic layer over desired minerals making them separated from gangue particles. It increases the floating ability of minerals by increasing the contact angle. Collectors of froth flotation can be anionic, cationic and non-ionic.