1. Flotation Reagents DMR Sekhar
FROTH FLOTATION
Flotation Reagents
DMR Sekhar

2. Contents Introduction Frothers Collectors Anionic collectors
Cationic collectors
Non-Ionic collectors
Amphoteric collectors
Non polar parts of collectors
Tall oil products
Adsorption of straight chain fatty acids
Adsorption of mixed fatty acids
Depressants
Activators
Pre activation
Promoters
pH modifiers
Summary
References

3. Introduction
Froth flotation is a process of separation of hydrophobic materials/minerals from hydrophilic ones.
Some minerals such as graphite are naturally hydrophobic and hence are naturally floatable.
Hydrophobicity may be induced to mineral surfaces by adsorbing certain surfactants called collectors.
Hydrophobic minerals are collected from flotation pulp into a froth phase.
frothers, collectors, depressants, activators, pH modifiers are other flotation reagents.

4. Frothers
Creating sufficiently stable froth is a prerequisite for flotation process.
This is achieved by reagents called frothers.
Methyl Iso butyl Carbinol (MIBC) is one popular frother. pine oil, eucalyptus oil, cresylic acid and long chain alcohols (amyl alcohol) are other known frothers. Functional group of frother should not have any affinity for mineral surface.
OH group of MIBC is
hydrophillic, non ionising
and CH3 groups (hydrocarbon chain)
are hydrophobic.
At water air interface OH groups
orient towards water and
hydrocarbon chain orients
towards air resulting into reduced surface tension of water at water air interface.
Methyl Isobutyl Carbinol

5. Collectors
Collectors are reagents that have non polar hydrocarbon chain attached to a polar functional group which interact with the mineral surface that is functional groups of collectors are solidophillic.
Depending on the charge of functional group collectors are classified as anionic, cationic, non ionic and amphoteric collectors.
Selectivity of collector adsorption largely depends on the composition and structure of functional group.

6. Anionic Collectors R O C O- Fatty acids or their soaps Xanthates
H+ or Na+
Fatty acids or their soaps
Xanthates
Dithiophosphates R O P S S-
Na+

7. Cationic Collectors
Lauryl Amine Hydrochloride R N+ H
Cl-

8. Non Ionic Collectors
Amyl Disulphide R S

9. Amphoteric Collectors
The functional group ionises to positive charge in acidic pH and negative charge in alkaline pH
In chemistry, an amphoteric species is a molecule or ion that can react as an acid as well as a base.
N- Sarcosine +

10. Non Polar Parts of Collectors
So far we showed non polar parts (which are hydrocarbon chains) of the collectors as R attached to their functional groups.
In the case of xanthates, dithiophosphates etc the hydrocarbon chains are ethyl/ propyl or butyl which are shorter.
Cationic collectors have lauryl or longer hydrocarbon chains.

11. Fatty acid collectors have mostly C18 fatty acids such as stearic acid (C18H35COOH), oleic acid(C18H33COOH) and Linoleic acid (C18H31COOH)
Stearic acid
Oleic acid
Linoleic acid

12. Tall oil Products
Tall Oil Fatty Acids (extracted from wood) or their soaps are used as Collector in industrial flotation. Abietic-type acids represents the majority 85-90% of typical tall oil extracted from wood.
Simmplified formula C20H30O2, or C19H29COOH

13. Adsorption of straight chain fatty acid anions
Solid (mineral) phase
Aqueous phase
1a. Compact layer of adsorbed saturated
fatty acid anions on a mineral surface.

14. Adsorption of mixed fatty acid anions
Aqueous phase
Solid (mineral) phase
1b. Fluffy layer of adsorbed mixed
fatty acid anions on a mineral surface.
fatty acids with cis double bonds are kinked
at the double bond. Double bonds may be hydrated due to its basic nature. Mixed fatty acids are specified in terms of iodine value, titer point and total fatty matter.

15. Depressants
Depressants are used to prevent the entry of unwanted minerals into froth phase.
Sodium silicate (Na2Sio3) is the depressant used in soap flotation of minerals to prevent the flotation of silica.
Cyanide (Na+ CN-) is a very selective depressant for pyrite and sphalerite while floating galena.
Dyes such as methylene blue are depressants for graphite.

16. Activators
Sphalerite (ZnS in cubic form) shows atypical flotation behaviour. While sphalerite in some ores showed native floatability others generally respond to Xanthate flotation only after “activation” by Cu ions.
Cyanide depresses sphalerite due to the formation of hydrophilic surface complexes. CN-, Zn(CN)2, Zn(CN)3-, Zn(CN)4- -
Cu ions added to the flotation pulp replace Zn from both zinc cyanide complex and zinc sulphide
Zn(CN)2 + Cu Cu(CN)2 + Zn (1)
ZnS Cu CuS Zn (2)

17. Pre Activation of Cyanide Depressed Sphalerite
Formaldehyde can break zinc cyanide complexes.
Zn(CN) HCHO CNCH2O - + Zn (3)
Equation (3) can replace equation (1) in the flotation of cyanide depressed sphalerite which is the pre step of activation mechanism and hence is termed pre activation.
Addition of formaldehyde prior to copper activation not only reduces copper (as copper sulphate) consumption but also improves the recovery of sphalerite selectively.

18. Promoters
Several flotation reagents may be grouped under promoters for example Light Diesel Oil is used to improve hydrophobicity imparted by hydrocarbon chains of fatty acids in soap flotation. LDO acts as hydrocarbon chain extender.
Detergents such as sodium petroleum sulfonate or alfa olefin sulfonate may be used along with soap collectors to improve the flotation efficiency and also to reduce the soap consumption.
Hydrotropes that enhance the dissolution of non polar solutes in water are being tested as promoters in soap flotation. Urea, sodium benzoate, sodium salicylate are promising.
Hydrotropes are similar to surfactants structurally but have shorter hydrocarbon chains.

19. pH Modifiers
Selectivity of flotation reagents, ionization of functional groups, formation of various chemical species of reagents added to the flotation pulp and adsorption on mineral surfaces is dependant on pH of the flotation pulp.
lime (CaO), Soda ash (Na2CO3), Caustic soda (NaOH) are used to adjust the pH in alkaline range.
sulphuric acid(H2SO4) is used to adjust pH of flotation pulp in the acidic range.

20. Summary
Flotation technique is115 years old. Much has been achieved in developing flotation reagents that are selective and so much needs to be achieved. Some industrial problems to look at are:
(1) Selective separation of graphite from sulphide ores.
(2) Recovery of fine sized (- 20 µm) galena and sphalerite from sulphide ores.
(3) Specifications of soap from mixed fatty acids for industrial flotation.
Industry and University interaction may be fruitful to attend the above problems.

21. References
Gaudin, AM., Principles of Mineral Dressing, Tata McGraw-Hill Publishing Company Ltd, New Delhi.1971
Glembotskii, V.A., Klassen, V.I., Plaksin,I.N., Flotation, Primary Sources, New York, 1972.
Houot, R., Beneficiation of phosphate ore through flotation: Review of industrial applications and potential developments, Int J Mineral Processing, 9 (1982) 352.
Sekhar D M R , Chauhan Y K, Soap Flotation Plant Practice in India, Trans Indian Inst. of Metals, 51(4) (1998).

22. References continued
Roy B K and Moulik S P, “Effect of hydro tropes on solution behaviour of amphiphiles” Current Science, 85(8) (2003).
Roux, E H, De Jager, D H, Du Plooy, J H, Nicotra, A, Van Der Linde, G J and De Waal, P, Phosphate in South Africa, Journal Southern African Institute of Mining and Metallurgy, 89(5):
DMR and CL Jain, Reengineering the Jhamarkotra phosphate concentrator, In the proceedings of XXIII International Mineral Processing Congress, 3 September, 2006, Istanbul, Turkey.

23. References continued
Sekhar, DMR., Srinivas, K., Prabhulingaiah, G., Dassin, Y and Alftinah, A., Promoters For Soap Flotation of Phosphate Minerals, XXV International Mineral Processing Congress (IMPC), Proceedings/ Brsibane, QLD, Australia, September, 2010
Srinivas, K and Sekhar, DMR, Comparitive Study of Jhamarkotra Soap Emulsion and Tall Oil Soap Emulsion as Flotation Collectors, Indian Chemical Engineer, Vol. 52 No. 3 July-September (2010)

24. Thanks
Thanks to Prof. ChVR Murthy, Principal, AU College of Engineering for making this Work Shop happen.
Thanks to Prof. V. Sujata, Prof. SV Naidu and
Prof. P. King and to the Department of Chemical Engineering for whole hearted support.
Thanks to Prof. TC Rao and DV Subba Rao Garu who are central to this work shop.