Concentration technologies: Basics

The objectives of concentration technologies is to separate the valuable mineral from the gangue minerals .In all concentration methods feed is divided in three streams, namely concentrate, middling and tailings. Middlings are recycled within the plant and as such the plant output is two products,  namely concentrate  and tailings. Tailings are disposed whereas concentrate is sent to metal extraction.


Plants Recovery and grade:

Recovery of the mineral in the concentrate and metal grade of the concentrate are important. Recovery is defined as
 
 

Grade of the concentrate can be defined either mineral grade or metal grade. Since concentrate is employed for metal extraction, metal grade is important (Note that concentrate contains mineral but not metal).

 

Metal grade means grade of valuable metal of the mineral in the concentrate. For example in the concentrate of chalcopyrite the grade of  is important. Similarly in the concentrate of galena, the grade of Pb is important. It must be clearly understood that ore does not contain metal. Metal grade is used to give an idea about the removal of gangue minerals and removal of oxygen or sulphur. For example mineral grade of pure  is unity but metal grade (or iron grade) of pure mineral  is 70% which means 30% oxygen has to be removed to get iron.

Recovery of a mineral in the concentrate can be 100% if all the feed is diverted in to concentrate. But metal grade will be very low. The maximum metal grade of the concentrate can be that of corresponding pure mineral, for example  grade in pure  is 34.1%, lead grade in pure  is 86.6%   grade in pure  is 67%. Consider 1000 kg feed of chalcopyrite which produces 1000 kg concentrate. The concentrate contains  and 10 kg Al₂O₃  .The analysis of feed is same as that of concentrate.

Now the recovery  in concentrate is 100%. But  grade in the