Lecture 4 Flotation 1 CHAPTER 6 FLOTATION CHEMICALS

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1 Lecture 4 Flotation 1 CHAPTE 6 FLTATIN CHEMICALS Contents: Action of the different reagents. Collectors, frothers, activators, depressants, ph modifiers. Natural hydrophobicity. Collectors: Collectors are organic molecules that render selected minerals water-repellant by adsorption of molecules or ions onto the mineral surface. Thus, the stability of the hydrated layer is reduced, and attachment of the particle to the bubble is achieved. Collectors are: Complex, organic molecules Not symmetrical in structure In two parts which differ in properties one polar and one non-polar Non-polar hydrocarbon chain Polar part The non-polar part has pronounced water-repellant properties, wheras the polar part reacts with water. The water repellant part is due to the strong bonding in the hydrocarbon radical (-C-C-). In contrast the polar part can react with water. Anion Cation H H H H // etc C C C C C \ H H H H Na eg structure of sodium oleate (CH3(CH2)7CH=CH(CH2)7CH) Collectors are used in small amounts. It is necessary to form a monomolecular layer on the particle surface. İf the concentration is increased, then the selectivity decreases. Collectors can be divided into a number of sub-groups based on the functional group involved and the type of mineral collected. Thio-compounds These are characterised by a functional group that contains a sulphur atom bonded to a carbon or phosphorous atom, but not to oxygen. These collectors are used in the flotation of sulphide minerals.

2 Lecture 4 Flotation 2 Anion Cation H H S // H C C C \ H H S Na Non-polar Polar Structure of sodium ethyl xanthate S P S Na (K) Dithiophosphates The sodium salts of a number of these collectors are presented below: Xanthate C S Na + S Di-thiophosphate S Na + \ P \\ S Di-thiocarbamate \ N C S Na + S Mercaptan S Na +

3 Lecture 4 Flotation 3 Thiourea Mercaptobenzothiazole \ N C S Na + N H N \ C S Na + \\ S They are short chain (from ethyl (2C) to hexyl(6c) or occasionlly octyl (8C) they are derivatives of carbonic acid, carbamic acid, phosphoric acid, urea and alcohols They are weakly surface active and have no frothing properties Adsorption occurs by chemical and electrochemical mechanisms rganic Acids and Salts the Anionics: These are ionisable, non-thio compounds derived from carbonic, sulphuric, phosphoric, phosphonic and arsonic acids Structural formulas of sodium salts of various aionic collectors Collector Type Structure Applications Carboxylate Na + (Fatty acids) Sulfonate Alkyl Sulfonate Hydroximate C \\ S Na + S Na + H C N Na + * Flotation of salt-type minerals, eg apatite, calcite, fluorspar, barite * ph should be alkaline * Very powerful * Used for oxides and silicates * Since bonding is electrostatic ph is critical * Used for oxides and silicates * Since bonding is electrostatic ph is critical Chelating agents. Very selective to certain metals

4 Lecture 4 Flotation 4 These are used to collect a wide range of oxide silicate and salt-type minerals. Because they are used to collect essentially hydrophilic minerals they have a more hydrophobic radical than the thiols. Carbon chains are 6 or 8 to about 20 or 22 Usually strongly surface active and exhibit powerful frothing properties Collector adsorption occurs by several mechanisms typically electrostatic attraction, chain-chain interaction, or chemical bonding rganic derivatives of ammonium hydroxide the Cationics: This group is represented by amines which, below certain ph values, exist in cationic form. Cation Anion \ N H - \ Cationic Amine Collector Unlike the xanthates they are considered to adsorb on the mineral surface primarily by electrostatic attraction They are very sensitive to the ph of the pulp being most active in slightly acidic solutions and are inactive in strongly alkaline and acid conditions. Amines are classified as primary, secondary, tertiary or quaternary, depending on the number of hydrocarbon radicals bonded to the nitrogen atoms see table Cationic collectors are used to float sylvite (KCl) from halite (NaCl), silica from phosphate rock, and for the flotation of sulphidised zinc carbonates and silicates Amine type collectors Amine Base Formula Primary amine NH2 Secondary amine 12NH Tertiary amine 2(2) 2N Quaternary amine 2(2)3N + Cl - Non-polar oils and hydrocarbons: A number of non-polar hydrocarbons and oils are used as collectors for readily or naturally floatable minerals (graphite, coal, sulphur, molybdenite, etc) or together with conventional collectors to to extend the hydropbobic effect of the primary collector. Examples are kerosine, naptha, fuel oils, and various resins.

5 Lecture 4 Flotation 5 Frothers: Frothers are surface active molecules whose function in the flotation system is to provide a large air-water interface of sufficient stability to ensure that a floated particle will not fall back into the pulp before it is removed. In flotation of non-sulphide minerals the collectors are normally strongly surface active reagents and so provide their own frothing action. With sulphide flotation, however, the thiol collectors are not adequately surface active hence frothers are necessary. A good frothers should have: Some solubility in water Negligible collecting power Produce a froth that is just stable enough to transfer the floated mineral from the cell to the collecting launder Frothers are generally hetero-polar surface active organic reagents, capable of being adsorbed on the air-water interface. When surface active molecules react with water, the water dipoles react readily with the polar groups and hydrate them, but there is practically no reaction with the non-polar group, the tendency being to force the latter into the air phase. Thus the molecules concentrate in the surface layer with the non-polar groups oriented towards the air and the polar groups towards the water. Water Polar Non-polar A Air Action of the frother The frothing action is due to the ability of the frother to: adsorb at the air-water interface because of its surface activity reduce the surface tension thus stabilising the bubble The most effective frothers are: Type Structure Comments Hydroxyl -H The alcohols (-H) are the most widely used since they have no collector properties Carboxyl -C= H Powerful collectors the presence of collecting and frothing properties in the same reagent may make selective flotation difficult Carbonyl =C= Amino group -NH2 Have weak collector properties

6 Lecture 4 Flotation 6 Sulpho group -S2H -S2H Have weak collector properties Examples are: Pine il contains aromatic alcohols, the most active frothing reagent being terpinols C10H17H has some collecting properties. Cresol contains cresylic acid CH3C6H4H. And also has wide use. Has some collecting properties MIBC (methyl isobutyl carbinol) A widely used synthetic alcohol frother. The composition of a synthetic frother is more stable than pine oil or cresol thus easier to control process. Fine textured, fairly selective froths, no entrainment, not excessive stability. Polyglycol Ethers synthetic frothers, form fine fragile froths, very selective, no collector action. Auxiliary eagents These are reagents that control conditions so that only the right particles float. Activators: Enhance collectot attachment to the valuable mineral. They are essentially inorganic compounds. Copper sulphate produces the Cu 2+ ion for the activation of, for example, ZnS, FeS2, Sb2S3, FeAsS. In the case of sphalerite, activation is due to the formation copper sulphide at the mineral surface, due to the fact that copper is more electro-negative than zinc and therefore ionises more readily ZnS + Cu 2+ CuS + Zn 2+ The copper sulphide deposited on the sphalerite surface reacts readily with xanthate, thus making the sphalerite surface hydrophobic. The main use of copper sulphate as an activator is in the differential flotation of lead/zinc ores after lead flotation the sphalerite is activated and floated. Sodium sulphide and hydrosulphide (Na2S and NaSH) for the activation, by sulphidisation, of oxidised minerals, and carbonates such as cerusite (PbC3), smithsonite (ZnC3) Sulphidisation causes sulphur ions to pass into the crystal lattice of the oxidised minerals, giving them a pseudo-sulphide surface coating and allowing them to be floated by thiol componds. For example, sulphidisation of cerusite: Na2S + H2 NaHS + NaH or PbC3 + 3NaH H2 + Na2C3 + NaHPb2 NaHS + NaHPb2 2NaH + PbS Na2S + PbC3 Na2C3 + PbS The amount of Na2S must be very strictly controlled since it is a very powerful depressant of sulphide minerals, and if used in excess depresses the activated oxide minerals preventing collector adsorption. Multivalent cations in the flotation of silicates using anionic collectors.

7 Lecture 4 Flotation 7 Activation ph ranges of different cations are listed below: Depressants: Metal Salt ph ange Fe Al Pb Mn Mg Ca Dpressants are used to incease the selectivity of flotation by rendering certain minerals hydrophilic, thus preventing their flotation. They can be either inorganic or organic compounds: Inorganic: o Cyanide Depresses sulphides of Zn, Cu, Fe, Ag, Cd, Ni and Sb because of greater stability of the cyano-complexes of these metals over the corresponding thio compounds 7Fe HCN Fe4[Fe(CN)6]3 + 18H + + 4e - o Chromate (Cr4) 2- or dichromate (Cr27) 2- depress PbS by the formation of the lead salt PbCr4 on the mineral surface o Sodium silicate Na2Si3 has a complex function of dispersant, depressant and froth modifier. It disperses and depresses siliceous gangue slimes. o Sodium sulphite Na2S3, pyrosulphite Na2S25 and S2 gas depresses sulphides of Zn and Fe generally in combination with ZnS4 and cyanide o Various carbonates, fluorides, phosphates and sulphates are used to depress the flotation of salt-type minerals with fatty acids rganic: Starch, tannin, quebracho and dextrin do not ionise in solution, but form colloidal particles in the pulp which can be deposited on the surface of the minerals, preventing flotation. Large quantities of these reagents will depress all minerals and they are not as selective as the inorganic depressants. They are used in small amounts to depress talc, graphite, and calcite. Starch is also used as a lead depressant in copper-lead separations. Tannin and quebracho depress calcite in fatty acid flotation of fluorspar and scheelite. Ph Modifiers: Essentially only four reagents are used for this purpose in the flotation industry. eagent Form of Addition Typical applications in addition to ph regulation Lime Ca, or Slaked lime Ca(H)2 Slurry Depresses pyrite and other iron sulphides Soda ash Na2C3 Dry Disperses gangue slimes

8 Lecture 4 Flotation 8 Caustic Soda NaH 5 10% solution Disperses gangue slimes Sulphuric Acid H2S4 10% solution Natural Hydrophobicity: Some materials are naturally hydrophobic, thus they float without the need of collectors and activators. Mineral Composition Contact Angle Graphite C 86 Coal Complex HC Sulphur S 85 Molybdenite MoS2 75 Stibnite Sb2S3 Talc Mg3(Si410)(H) 2 88 f these, talc is particulariy important as it is widespread in siliceous ores and can float with values thus diluting the concentrate. Depression of talc may be needed. Graphite can also be a problem for the same reason. Graphitic and carbonaceous material often occurs in sedimentary ore bodies and once again can lead to contamination of concentrates. A prefloat is sometimes used to remove such materials before conditions are set for the major flotation.

Lecture 6 Flotation 1. Chapter 8_Flotation of Non-Sulphide Minerals

Lecture 6 Flotation 1. Chapter 8_Flotation of Non-Sulphide Minerals Lecture 6 Flotation 1 Chapter 8_Flotation of Non-Sulphide Minerals Contents: Oxides & silicates. Adsorption & chemisorption of collectors. Activation & depression. Silica, feldspar, calcite, phosphates.