Metallurgical recovery
- Also known as
- recovery, mineral recovery, flotation recovery
Metallurgical recovery is the percentage of the valuable metal or mineral in the ore fed to a processing plant that ends up in the final product, such as a concentrate or refined metal. The rest is lost, mainly to the tailings.
What is metallurgical recovery?
Metallurgical recovery, usually just called recovery, measures how much of the valuable metal a plant captures. If the ore fed to a flotation plant contains 100 metric tons of copper and 90 metric tons end up in the concentrate, recovery is 90 percent. The other 10 metric tons are lost, almost entirely to the tailings.
Recovery can be stated for a single stage, such as a rougher flotation bank, for a whole circuit, or for the entire operation from ore to refined metal.
How recovery is calculated
When the masses of all streams are known, recovery is simply the metal in the product divided by the metal in the feed. Plants often cannot weigh every stream, so recovery is commonly calculated from assays using the two-product formula:
Recovery (%) = 100 × c × (f − t) ÷ [f × (c − t)]
where f is the feed grade, c is the concentrate grade and t is the tailings grade. The formula follows from a mass balance and is widely used for daily plant accounting and test work.
A related figure is mass pull, or yield: the share of the feed’s total mass that reports to the concentrate.
Recovery and grade
Recovery and concentrate grade tend to move in opposite directions. Recovering more of the valuable mineral usually means accepting more gangue in the concentrate, which lowers its grade. Rejecting gangue more aggressively usually loses some valuable mineral. This trade-off is captured by the grade-recovery curve. The economic optimum depends on metal prices, smelter terms and costs; improvements in flotation selectivity or mineral liberation shift the curve so that both can improve.
What limits recovery
- Liberation. Valuable mineral locked inside gangue particles cannot be recovered by surface-based processes.
- Particle size. In froth flotation, very fine and very coarse particles are recovered less efficiently.
- Reagent performance. Insufficient or poorly matched collector leaves valuable mineral unfloated.
- Ore variability. Oxidation, clay content and mineralogy change from one part of the orebody to another.
- In leaching, solution contact, heap leach channeling and leach time.
Why recovery matters
Because processing costs are incurred on every metric ton of ore, small changes in recovery have large effects on revenue. A one-percentage-point gain in recovery at a large mine can be worth millions of dollars a year, which is why plants test reagents and operating changes carefully. As ore grades decline, recovery becomes even more important to project economics.
Recovery and Locus biosurfactants
Locus Mining describes its biosurfactant-based reagents as improving recovery in flotation while maintaining concentrate grade, and as improving solution contact and metal recovery in heap leaching.
Frequently asked questions
Either directly, as the mass of metal in the product divided by the mass of metal in the feed, or from assays with the two-product formula, 100 × c × (f − t) ÷ [f × (c − t)], using feed, concentrate and tailings grades.
It depends entirely on the ore and the metal. Some sulfide ores routinely achieve recoveries above 90 percent, while complex, fine-grained or oxidized ores may achieve much less. Recovery is best judged against the ore’s own test work and the grade achieved at the same time.
Recovery is the share of the valuable metal captured in the concentrate. Yield, or mass pull, is the share of the total feed mass that reports to the concentrate.
Sources
- Wills' Mineral Processing Technology, 8th edition, B. A. Wills and J. A. Finch, Butterworth-Heinemann, 2016
- SME Mineral Processing and Extractive Metallurgy Handbook, Society for Mining, Metallurgy and Exploration, 2019