Outotec and Teck Cominco have conducted test-work to determine the best thickening solution for flotation tailings, flotation concentrate, and post CN destruction CIP tailings stages at Pogo mine. Karl Dietz writes.
The first gold from the Pogo mine was poured 12 February 2006.
The Pogo Mill flow-sheet consists of SAG and ball mill grinding, followed by gravity recovery, flotation, ultra-fine regrinding, cyanidation, and thickening.
The plant disposes of most tailings underground as paste backfill, while remaining tailings are filtered and dry-stacked on the surface.
The need to maximise water recovery from tailings was critical to gaining the environmental permits necessary for the project.
The permits for tailings and water management led to additional thickener test-work in October 2003, to test the water balance of the mill.
Close client collaboration
Outotec (formerly Outokumpu Technology), working closely with Teck Cominco, developed a test campaign to determine the best thickening solution for three critical thickening stages in the Pogo flow-sheet, and to confirm the water balance.
The three streams tested were the flotation tailings, the flotation concentrate, and the post CN destruction CIP tailings.
The test program was conducted at SGS Lakefield Research (Canada) in October 2003, using samples that had been stored in a frozen state from the Pogo pilot plant.
The objective of the testwork was to confirm the densities required to complete the water balance in a continuous, dynamic system, and ascertain the best thickening technology to effectively handle these densities.
The test-work consisted of initial bench scale testing in Outotec’s 94 mm bench scale high-rate thickener, with subsequent testing in Outotec’s 190 mm mini-pilot paste thickener.
The bench scale thickener has been used successfully to size hundreds of high rate thickeners globally, while the 190 mm dynamic mini-pilot thickener enables the effects of bed compression and rake design to be investigated. This minimised the need for scale-up adjustment, in many cases, proven to be 1:1 with industrial applications.
The continuous steady-state operation of the 190 mm mini-pilot paste thickener allowed rheology data to be collected, ensuring accurate sizing and design.
Test-work resulted in optimal engineering through the addition of mechanical design features.
These features included rotating and static pickets, currently under patent by Outotec, able to achieve targeted underflow densities with no evidence of rotating bed formation.
A Concentric Shear Thinning arrangement has ensured reduction in yield stress for transportation of the thickened slurry. This system is working in conjunction with the rotary lobe pumping system.
Results from the plant after five months of operation indicated that the 10 m pre-leach SUPAFLO paste thickener was operating at an average density of 52% solids compared to 47% to 48% in the mini-pilot.
Over the same period, the 12 m SUPAFLO high compression tailings thickener has had an average underflow density of 60% solids compared to 62% to 62.4% in the mini pilot.
The CIP tailings and CN Recovery thickeners, using two 7 m SUPAFLO paste thickeners, are both able to achieve 49% solids.
The torque values for all thickeners are said to show good correlation with the design point of 25% of the maximum design output torque for normal operation at the design densities.
The test-work has ensured complete confidence during scale-up, as the Pogo thickeners have been field-proven.