Fractional recovery, also referred to as metallurgical recovery or extraction efficiency, is the proportion of the valuable mineral or metal that is successfully extracted from the run-of-mine (ROM) ore during processing, expressed as a decimal fraction or percentage. It is one of the most important key performance indicators (KPIs) in any mining and mineral processing operation, directly determining the economic value generated per tonne of ore mined and processed in bauxite, gold, iron ore, and diamond mining.
Fractional recovery is influenced by a combination of mineralogical, process, and operational factors. Mineralogical factors include the grain size and liberation characteristics of the valuable mineral, the nature of the host and gangue minerals, the degree of interlocking or occlusion of the ore mineral within the gangue, and the presence of penalty elements or deleterious minerals that interfere with extraction. Process factors include the comminution (crushing and grinding) circuit design and its ability to achieve adequate liberation without over-grinding, the efficiency of the separation process (flotation, gravity, leaching, magnetic, electrostatic), reagent selection and dosage, and process water quality.
In bauxite processing, the Bayer process fractional recovery of available alumina is typically 85–92%, depending on the silica-to-alumina ratio and the reactive silica content of the ore. In gold mining, fractional recovery varies widely — from over 95% for free-milling gravity-recoverable ores to below 80% for complex refractory sulfide ores where additional pre-treatment is required. In iron ore processing, recovery of iron to the product concentrate from a magnetic separation circuit may range from 75% to 95%, depending on ore grade and liberation characteristics. In diamond mining, recovery is critical due to the extremely high value of individual stones; any unrecovered diamond represents a direct and significant revenue loss, and total plant diamond recovery must account for losses through all unit operations including screening, DMS, and final recovery.
Continuous improvement of fractional recovery is achieved through ore characterization studies, process audits, mass balancing, and metallurgical test work programs, all aimed at identifying and reducing specific process losses.