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Minerals: separate to accumulate

26th October 2015

Posted By Paul Boughton


Frothers support coarse particles in large flotation machines
Mineral liberation analysis begins in the lab
A number of design issues must be considered for concentrators and mills that treat high tonnages of ore

Simon Isherwood presents the latest solutions in the mineral separation sector

Flotation is the most widely used method for separating minerals. It uses the natural hydrophobicity of the valuable minerals to be floated and has been used since the 19th century.

Development of the chemicals used in the flotation 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 in the century and is ongoing. The latest techniques of mineral liberation analysis (MLA) using quantitative scanning electron microscopy are impacting reagent choices and treatment strategies.

There are several common families of chemicals used in mineral separation by froth flotation. 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 flotation and were all developed by the 1950s. Since then, there have been modifications 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 flotation, have all been available for many years ¬– development here has been in the application technology.

Frothers

Frothers are another commonly used tool in mineral separation. Frothers are used to modify the surface tension of liquids to allow fine 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. These have been superseded by glycols, glycol ethers and synthetic alcohols.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 tonnages of ore at coarse grinds and use larger flotation machines, the frother has to support and allow drainage of coarse particles in the froth bed. Often frothers are not needed in industrial mineral flotation due the foaming action of many cationic collectors but they are used widely in coal flotation. MIBC, which has been traditionally used in easier to float coals is often replaced with mixes of glycol ethers and higher alcohols as poor floating coal is are increasingly cleaned by flotation.

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. These are now complemented by synthetic materials that can be manufactured with specific characteristics to give precise performance. Carboxy methyl cellulose, modified polysaccharides and various amines can be used to control gangue minerals in pgm, gold and nickel flotation. For the control of pyrrhotite some new chemicals are currently being commercialised.

Last on the list are modifiers. These comprise everything from pH controlling agents to mineral surface activators or depressants and dispersants. These are often commodity type chemicals and are bought on specification and price.

Nasaco and Betachem are specialists in the design, development, production and marketing of chemicals for flotation and associated mineral processes. The founders of the companies were mineral processing engineers who realised that flotation chemicals should be approached in a different way. They felt that existing chemical products were limited in scope and were not tailored sufficiently to address individual processing problems.

The two companies are working together with operators to solve processing problems chemically. By combining chemical properties from the best chemical raw materials available they can solve most problems efficiently and cost effectively and can provide monitoring of processes to ensure continuing success. Both companies have mineral processing engineers working globally. Their engineers are based in Europe, Africa, and Australasia and are closely associated with several companies in Latin America.

From the two firms’ initial focus on flotation and frothers and collectors, they have developed technology and expertise in depression and activation of minerals as well as dewatering and thickening processes. Many technical innovations occur while working together with their customers.

Development work starts in their research laboratories in South Africa, where, as well as the standard mineral processing test equipment, they have a highly sophisticated MLA electron microscope. This is used for fundamental work, as well as for customer circuit analysis and problem solving.

Simon Isherwood is with Nasaco









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