SPECIALIST EQUIPMENT SEPARATE to ACCUMULATE Simon Isherwood presents the latest solutions in the mineral separation sector F
lotation is the most widely used method for separating minerals. It uses the natural hydrophobicity of the valuable minerals to be fl oated and has been used since the 19th century.
Development of the chemicals used in the
fl otation process occurred quickly during the early 20th century. Understanding of the actual interactions between the various chemicals and minerals, and the wider relationship between chemistry, the mechanical and design aspects of the machines and the optimisation of the ore types being treated developed later and is ongoing. T e latest techniques of mineral liberation analysis (MLA) using quantitative scanning electron microscopy are impacting reagent choices and treatment strategies. T ere are several common families of chemicals used in froth fl otation. Firstly, there are collectors, which preferentially adsorb onto mineral surfaces to make them hydrophobic. Dithiophosphates, xanthates and derivatives, as well as thionocarbamates are used for sulphide fl otation and were all developed by the 1950s. Since then, there have been modifi cations of these chemicals and knowledge of their performance characteristics has developed, but there has been little new chemical innovation. Amines and sulphonates for industrial mineral, and hydrocarbons for coal fl otation, have all been available for many years – development here has been in the application technology.
The role of frothers Frothers are another commonly used tool in mineral separation. Frothers are used to modify the surface tension of liquids to allow fi ne bubble generation and to produce stable froth beds that allow concentration of the minerals in the froth. Originally these tended to be pine oil and cresylic-acid based chemicals. T ese have been superseded by glycols, glycol ethers and synthetic alcohols. Frother selection is critical. In the design of new concentrators and mills that treat high
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tonnages of ore at coarse grinds and use larger fl otation machines, the frother has to support and allow drainage of coarse particles in the froth bed. Often frothers are not needed in industrial mineral fl otation due the foaming action of many cationic collectors but they are used widely in coal fl otation. MIBC, which has been traditionally used in easier to fl oat coals is often replaced with mixes of glycol ethers and higher alcohols as poor fl oating coal is are increasingly cleaned by fl otation.
Depressants are next on the list of mineral separation solutions. Depressants are used to control gangue minerals, particularly talc and other silicates as well as slime material. Traditionally, naturally occurring starches and guars were used. T ese are now complemented by synthetic materials that can be manufactured with specifi c characteristics to give precise performance. Carboxy methyl cellulose, modifi ed polysaccharides and various amines can be used to control gangue minerals in pgm, gold and nickel fl otation. For the control of pyrrhotite some new chemicals are currently being commercialised. Last on the list are modifi ers. T ese comprise
everything from pH-controlling agents to mineral surface activators or depressants and dispersants. T ese are often commodity type chemicals and are bought on specifi cation and price.
Frothers support coarse particles in large fl otation machines
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