Froth flotation cell

Graphite Physical Processing

Each graphite ore has unique characteristics which need to be adressed in the processing. Therefore it is of crucial importance to determine graphite flake morphology, primary flake size and liberation size. Typical flake graphite deposits are gneissic, i.e. they consist mainly of feldspar, quartz and mica.

The size of the graphite flake is a very important commercial consideration. Therefore, it is in the best interest of a flake graphite producer to maximize the amount of large flake removed from the deposit. This means that any processing which will tend to grind or reduce the size of constituent flake must be minimized. Based on aforementioned ore specifics the appropriate degree of grinding and liberating is defined. Typically graphitic ore is crushed in cone crushers or vertical shaft impactors (in large scale), ground in roller mills and classified. Grinding is carried out in a most gentle manner trying to avoid breaking valuable coarse graphite flakes when comminuting granular side minerals such as quartz and feldspar. Preferably shearing grinding techniques such as ball or rod mills are used to achieve this target.

The crushed and ground graphitic rock is then subjected to froth flotation. Froth flotation takes place in a water-mineral suspension. It is used for selectively separating minerals by taking advantage of differences in their hydrophobicity. The surfaces of the graphite particles are hydrophobic (water-repellent) and it is thus very amenable to flotation in water using suitable/selective conditioning reagents. Hydrophobic graphite particles become attached to air bubbles that are introduced into the suspension and are carried to a froth layer above the liquid, thereby being separated from the hydrophilic (wetted) particles. In contrast the flotation reagents do not stick to the country rock; therefore these particles sink to the bottom of the cell and are removed from the process. Flotation beneficiated flakes may be re-floated to increase its purity.

Flotation process designs vary in complexity depending on degree of liberation and the desired purity of the product but will typically include several rougher, liberation and cleaner flotation steps with intermediate regrinding steps.

Flake which is in the purity range of 80-98% typically represent materials which have been beneficiated using only froth flotation. Although surface chemistry provides the mechanism by which flotation is affected, the process cannot change the purity of the discrete graphite particle. Such remaining impurities finely intergrown with the graphite can then be removed by applying chemical or thermal treatment steps to achieve highest purity grades.