Separation techniques mineral processing

Flotation. Flotation is a gravity separation process which exploits differences in the surface properties of particles. Gas bubbles are generated in a liquid and become attached to solid particles or immiscible liquid droplets, causing the particles or droplets to rise to the surface. This is used to separate mixtures of solid-solid particles and liquid-liquid mixtures of finely divided immiscible droplets. It is an important technique in mineral processing, where it is used to separate different types of ore. 

Biological processes are also being studied to investigate abiHty to remove sulfur species in order to remove potential contributors to acid rain (see Air pollution). These species include benzothiophene-type materials, which are the most difficult to remove chemically, as weU as pyritic material. The pyrite may be treated to enhance the abiHty of flotation processes to separate the mineral from the combustible parts of the coal. Genetic engineering (qv) techniques are being appHed to develop more effective species. 

An earlier section which dealt with mineral separation included flotation among the category of concentration separation processes. The introduction of flotation was one of the major milestones in the history of mineral processing. There exist variations (natural or artificially created) in the surface properties of mineral particles, and the technique of flotation is based on the utilization of these differences. The actual specific gravity of the mineral particle plays little or no part in the separation. 

The equipment used for solid-solid separation processes was developed primarily for the minerals processing and metallurgical industries for the benefication (up-grading) of ores. The techniques used depend on differences in physical, rather than chemical, properties, though chemical additives may be used to enhance separation. The principal techniques used are shown in Figure 10.1 which can be used to select the type of processes likely to be suitable for a particular material and size range. 

Froth-flotation is an extensively used separation technique, having a wide range of applications in the minerals processing industries and other industries. It can be used for particles in the size range from 50 to 400 //m. 

After mixing for an appropriate time, clean soil particles and wash water containing the dissolved and suspended contaminants are separated. Separation techniques in soil-washing systems are similar to those applied in the mineral-processing industry.78 The most common separation techniques are as follows ... 

Flotation is an important technique in mineral processing, where it is used to separate different types of ores. When used to separate solid-solid mixtures, the material is ground to a particle size small enough to liberate particles of the chemical species to be recovered. The mixture of solid particles is then dispersed in the flotation medium, which is usually water. The mixture is then fed to a flotation cell, as illustrated in Figure 8.12a. Here, gas is also fed to the cell where gas bubbles become attached to the solid particles, thereby allowing them to float to the surface of the liquid. The solid particles are collected from the surface by an overflow weir or mechanical scraper. The separation of the solid particles depends on the different species having different surface properties such that one species is preferentially attached to the bubbles. A number of chemicals can be added to the flotation medium to meet the various requirements of the flotation process ... 

Cadmium acetate is used in the pottery and porcelain industry for producing iridescent effects the borotungstate forms an aqueous solution of high density when concentrated (d = 3.28), useful in die mechanical separation of minerals and in density gradient techniques the bromide, like the zinc salt, is used in photography, process engraving and lithography. 

The crude monazite sands are first concentrated by the general mechanical and physical treatments of mineral dressing. Brazilian monazite sands are processed mainly by the electromagnetic separation technique. The Indian monazite industry is essentially based on the recovery of rutile and ilmenite. Ilmenite has a magnetic susceptibility very close to that of monazite and thus direct electromagnetic separation cannot be applied to the Indian Travancore monazite sands. 

Materials mined from a mineral deposit usually consist of a heterogeneous mixture of solid phases that are generally crystalline and contain various minerals. Crushing and grinding operations are used to liberate the mineral species from one another and to reduce the size of the solids to a range suitable for subsequent processing. Of the various separation techniques, those of froth flotation and agglomeration exploit the chemical and physical properties of the surfaces of minerals, which can be controlled by various chemical interactions with species in an aqueous phase. 

G. Dodbiba, N. Haruki, A. Shibayama, T. Miyazaki, and T. Fujita, Combination of Sink-float Separation and Flotation Technique for Puriflcation of Shredded PET-bottle from PE or PP Flakes , Int. J. Mineral Processing 65, 11-29 (2002). 

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