Molybdenum Processing Solution

Molybdenum is unusual among flotation ores: molybdenite (MoS2) is one of the most naturally floatable minerals there is, so getting it to float is easy. The difficulty is grade. Final molybdenum concentrate must reach 45-57% Mo, far higher than most base-metal concentrates, which means the rougher concentrate has to be cleaned many times over. The flowsheet is therefore defined less by the rougher and more by a long, carefully staged cleaning train.

Why bulk flotation then heavy cleaning

Molybdenite has a layered, graphite-like crystal structure that is naturally hydrophobic, so it floats with little more than a hydrocarbon oil collector (such as diesel or kerosene) and a frother, no expensive sulphide collector needed. A rougher-scavenger circuit quickly recovers nearly all the moly into a bulk concentrate, but at a low grade because fine gangue and middlings float with it. Reaching a saleable 45-57% Mo then requires re-floating that concentrate five to eight times, with a regrind early in the cleaning train to liberate gangue trapped in molybdenite flakes. Each cleaner rejects more gangue; the trade-off is that aggressive cleaning can lose moly, so stage count and regrind size are tuned to the ore.

The recommended flowsheet

Crushing, grinding and classification

Ore is crushed with a jaw crusher and cone crusher, then ground in a wet ball mill closed with a hydrocyclone cluster to 55-70% passing 75 micron. Molybdenite is soft and flaky, so grinding is set to liberate without over-sliming, which would smear moly across the froth and hurt selectivity.

Rougher flotation and multi-stage cleaning

The rougher circuit, built from mechanical flotation cells, floats a bulk concentrate with oil collector and frother. That concentrate is reground and sent through a long cleaner train, a packaged flotation plant can be configured for the rougher and cleaner stages, with the full flotation equipment range covering cell sizing. Sodium silicate or other depressants hold back silica and talc through the cleaners to protect grade. For the selective-separation principles behind cleaner circuits, see our copper flotation flowsheet guide.

Copper-molybdenum separation

In porphyry ores moly is a by-product of copper, and the two float together into a bulk Cu-Mo concentrate. Separation reverses the usual logic: the easily floated molybdenite is floated again while copper sulphides are depressed (commonly with sodium hydrosulphide or Nokes reagent), yielding a clean moly concentrate and a copper concentrate. This is a specialized circuit that needs careful reagent control.

Dewatering

The finished moly concentrate is thickened on a thickener and filtered to a low-moisture cake for shipment to a roaster.

Design choices that drive results

• Number of cleaner stages: the dominant control on final grade; more stages lift grade but risk moly loss.
• Regrind size: liberates gangue locked in molybdenite flakes and is essential to reach 50%+ Mo.
• Gangue type: talc and carbonaceous matter float naturally and dilute the concentrate, so depressant choice is critical.
• Cu-Mo ratio: in porphyry ores, decides whether a dedicated copper-molybdenum separation circuit is warranted.

Molybdenite grade and the cleaning effort needed vary with gangue mineralogy, so the cleaner train and regrind must be designed from testwork. Xinhai runs the ore test, designs the rougher and multi-stage cleaner circuit and delivers the complete processing plant under an EPC+M+O contract. To define the cleaning circuit for your ore, contact us for an ore test.