Guizhou Phosphate: P₂O₅ +2.6pt, SiO₂ −3.0pt in One Pass

Dense medium separation simultaneously raised phosphate grade and rejected silica — and proved the tailings recyclable.

Test data (0.5–12 mm)

Dual-objective separation

For phosphate, the payoff is twofold: grade above the commercial threshold and silica below the acid-plant penalty line. Density separation achieves both in a single pass, without reagents.

Ore & background

Guizhou hosts China's largest phosphate province, dominated by sedimentary collophane ores where silica is the persistent enemy: every point of SiO₂ in concentrate costs acid-plant efficiency and incurs commercial penalties. The task was therefore two-dimensional from the start — raise P₂O₅ and depress SiO₂ in the same operation.

Reading the results

The single density cut delivered both objectives: P₂O₅ up 2.58 points to 29.92% at 96.26% recovery, SiO₂ down 3.0 points to 8.34% with 34.28% of the silica rejected. A 29.9% concentrate sits comfortably above common commercial-concentrate thresholds (≥28–30% P₂O₅), achieved without reagents — leaving the full flotation toolbox in reserve if a premium product is later required. The rejects at 8.48% P₂O₅ additionally proved lean enough to consider for construction-materials use.

Test conditions

Test methodology

The ore was first wet-screened to remove the −0.5 mm slimes (evaluated separately for flotation). The 0.5–12mm fraction was fed to a ferrosilicon/magnetite suspension; a density-gradient series located the optimum cut density, after which the sample was passed once through a pressurized two-product cyclone. Products were drained on sieve bends, rinsed on drain-and-rinse screens, dewatered, sampled and assayed to compute yield, grade and recovery. Dilute medium was recovered by magnetic separation and densified back to the correct-medium sump under closed-loop density control.

Industrial significance

For integrated phosphate-chemical producers the arithmetic runs through the acid plant: less silica per tonne of P₂O₅ means less energy, less wear and fewer penalties. And because the test also characterized the tailings, it doubled as a feasibility screen for the companion question — what value is still sitting in Guizhou's legacy tailings piles.

Frequently asked questions

Q: What recovery did dense medium separation achieve on this phosphate ore?
A: 96.26% P₂O₅ recovery into a 29.92% concentrate, with SiO₂ cut from 11.34% to 8.34% (0.5–12 mm).

Q: Will this work on my phosphate deposit?
A: Density separation depends on liberation size and density contrast, not on locality. A one-tonne representative sample answers the question definitively — washability results within 24 hours of sample receipt.