Degree of liberation

One of many things affected to the efficiency of mineral processing is degree of liberation. In order to understand perfectly about degree of liberation, we must understand about the liberation it self. Hence we can get a full picture of why the degree of liberation affect the mineral processing.


The goal of liberation is to obtain particles of pure mineral, so the valuable mineral can detach from the gangue. In easy way, liberation is about to release the valuable minerals from their waste gangue. Liberation is achieved through size reduction which take place in crushing and or grinding equipment. Comminution produces valuable mineral particles, gangue particles and locked particles (middlings). The latter may or may not have economic value. Adequate liberation occurs when mainly two types of particles are produced and can be economically separated. Those two types are particles contain mostly valuable mineral and contain mostly gangue.

example of mineral liberation
mineral liberation illustration

There are a number of ways to represent liberation. One method is to calculate the liberation spectrum using microscopic techniques. The spectrum shows weight distribution of particles by percent valuable minerals. It gives a clear picture of how easy or difficult a separation might be. The other way to represent liberation is by the degree of liberation, in fact this is the famous method to represent liberation.


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Degree of liberation

The degree of liberation refers to the percentage of a mineral occurring as liberated, or free particles of pure mineral in relation to the total amount of that mineral present in the ore. The degree of liberation depends on the size of the particles compared to the size of the grains. High particle size to grain size ratios give poor liberation. Similarly too many grains of different minerals in a single particle. Low particle to grain size ration suggest good liberation, correspondingly to few grains in a single particle.


Illustrated graphic for degree of liberation
Degree of liberation chart

For a given particle size, different minerals often have different degree of liberation. Typically the gangue mineral is liberated at coarser sizes than the valuable mineral.

Liberation generally increases as the particle become smaller. This means that for a given group of particles, one could divide them into different size fractions. Look at the liberation spectrum for each size fraction. As expected, liberation is better in the finer sizes and it should be easier to make a separation in this size range.

Liberation Spectrum of chalcopryrite minerals
Chalcopyrite Liberation Spectrum

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