Recovery of P2O5 from Phosphate Mine Tailings and Slimes Curtis Griffin Process Supervisor

AGENDA Review basic beneficiation flow sheet. Discuss slime generation from de-sliming hydrocyclones. Discuss tailings generation from flotation process. Review pilot plant testing on recovery of P2O5 from slimes. Review pilot plant testing on recovery of P2O5 from tailings.

Phosphate Plant Beneficiation Flow Sheet Matrix +3/8 inch +16 mesh Pebble (Phosphate) Debris Washer De-sliming Hydrocyclones -150 mesh Clay/Slimes +20 mesh IP (Phosphate) Sizers -35 mesh -20 mesh Fine Flotation Coarse Flotation Acid Wash/Rinse Amine/Cleaner Flotation Tailings to Mine Amine Concentrate (Phosphate)

P2O5 Loss From De-Sliming P2O5 is lost as slimes (ultra fines) during de-sliming step with hydrocyclones. Typically as much as 33-37% of matrix feed will be lost as slimes. P2O5 content of slimes is typically 2 - 13% Challenge with recovery of P2O5 from slimes is ultra fine (– 150 mesh) with colloidal particles, typical flotation is difficult. Pilot work was done in conjunction with EcoPhos for recovery of P2O5 from slimes.

Recovery of P2O5 From Slimes PegasusTSI in conjunction with EcoPhos performed pilot testing. Used EcoPhos process. EcoPhos process uses HCL to dissolve phosphate followed by precipitation of dissolved P2O5 as Di Calcium Phosphate (DCP). Pilot testing converted slimes into DCP.

Recovery of P2O5 From Slimes X-Ray analysis showed most of the P2O5 was in the form of: Calcium hydrogen phosphate hydrate: Ca8H2(PO4)6. 5H2O Brushite: CaHPO4. 2H2O

Recovery of P2O5 From Slimes Step 1: slimes were dissolved in diluted HCL at various HCL/Ca ratios. Step 2: the products were analyzed to determine process yield. Step 3: calcium carbonate was added to produce DCP. One ton of slime produced 0.27 t DCP. Recovery of 76%.

DCP Analysis from Slimes Unit Slime DCP P2O5 % 13.1 38.3 CaO 17.92 36.54 Al2O3 11.71 .07 Fe2O3 8.14 .18 MgO .9 .003 Na2O .066 .004 K2O 2.650 .005 As Ppm 7.1 <.5 Cd 1.4 Cr 140 1.21 Pb 3.9 5.5 Sr Ppm, 1000 32.91 Hg <.1 .2 F .69

P2O5 Loss From Flotation Process as Tailings P2O5 is lost with tailings during the flotation process. Typically 30 – 33 % of the matrix feed is lost as tailings. P2O5 content of tailings is typically 2.5 - 6%.

Recovery of P2O5 from Tailings PegasusTSI worked in conjunction with Florida Industrial and Phosphate Research Institute (FIPR). Dr. Haijun Liang with FIPR performed flotation pilot testing. Denver cell mechanical flotation with aeration. Collector was a fatty acid.

Jameson flotation cell schematic

Pilot Denver Flotation Cell

Chemical Analysis of Head Sample (wt%) P2O5 Insol MgO Fe2O3 Al2O3 CaO 2.49 86.11 .03 .29 .28 4.25

%P2O5 Recovery VS Collector Addition

Results of Testing 82.07% P2O5 recovery. 26.37% P2O5 in tailings float concentrate.

Phosphate Plant Beneficiation Flow Sheet Matrix +3/8 inch +16 mesh Pebble (Phosphate) Debris Washer De-sliming Hydrocyclones -150 mesh Clay/Slimes +20 mesh IP (Phosphate) Sizers -35 mesh -20 mesh Fine Flotation Coarse Flotation Acid Wash/Rinse Amine/Cleaner Flotation Tailings to Mine Amine Concentrate (Phosphate)

Overall Impact on P2O5 Recovery Each beneficiation plant is different, but typical P2O5 recovery is around 90%. Potential of 10% additional P2O5 recovery. Slimes test work showed P2O5 recovery 76%. Tailings flotation test work showed P2O5 recovery of 82%. Assuming 3% P2O5 in tailings and 7% P2O5 in slimes.

Overall Impact on P2O5 Recovery 5.04% P2O5 increase from slimes. 2.46 % P2O5 increase from tailings flotation. Total P2O5 recovery could be as high as 97.5% or 7.5% increase in P2O5 recovery. Pilot testing on each specific slimes and tailings. Next step would be to do economic evaluation.