1. ` Soluble Metal Recovery Improvement Using High Density Thickeners in a CCD Circuit Ruashi II a Case Study February 2009 M. Mulligan (Presenter) L. Bradford

2. ` Agenda n Introduction n Thickener technologies n Lab Simulations n CCD Simulations n High Density vs High Rate Thickeners

3. ` Introduction n Ruashi is a Copper/Cobalt mine in the DRC n Circuit overview: Leach-CCD-SX-EW n Copper recovery is critical in the CCD circuit n Lab & CCD simulations to optimise recovery n Selection and design of the best thickener technology

4. ` Thickener Development Conventional High Rate – flocc + dilution High density – flocc + dilution + compression Paste – flocc + dilution + compression + residence time

5. ` Different Thickener Technologies

6. ` Counter Current Decantation (CCD)

7. ` Lab Simulations

8. ` n Sedimentation testwork done within hours of the leach done at Mintek n Settling & flocculant flux curves n 4 litre batch tests n 4 litre continuous tests n Rheology

9. ` Optimal % Solids for Settling Optimum = 7% – 8%

10. ` Optimal Flocculant Dosage Optimum = 50g/t

11. ` Underflow % Solids vs Time Batch: 55% Continuous: 59%

12. ` Rheology n Haake Viscometer n Measure yield stress of thickener u/flow n Info used to size rake drive

13. ` Rheology 60 Pa at 59% Solids

14. ` CCD Simulations

15. ` Variables used in base case simulation Wash Ratio U/F Suspended Solids Concentration (wt%) Feed Suspended Solids Concentration (wt%) Soluble Cu Recovery (%) 1.65530+99

16. ` CCD Wash Recovery

17. ` Sensitivity to Wash Ratio

18. ` Sensitivity to Underflow % Solids

19. ` Counter Current Decantation (CCD) U/f % Solids: 59% Wash Ratio: 1.6 RECOVERY: > 99%

20. ` High Density vs High Rate

21. ` High Density vs High Rate Thickeners CCD wash recovery l HD always has higher wash recovery per stage for a given wash ratio Capital cost implications l Per thickener cost is similar – HD diameter smaller l Overall CCD plant costs less with HD – less stages required

22. ` Increase in Income Based on 5 stages. Wash ratio = 1.6

23. ` Thickener Design Differences n Higher tank sidewall depth n Steeper tank floor slope n Higher rake mechanism torque n Rake mechanism – Pickets n Thickener discharge cylinder

24. ` Conclusions n Lab simulations & CCD simulations are important for decision making and design of a CCD plant n 5 High Density thickeners give a better recovery than 6 High Rate thickeners for Ruashi n Capex and Opex costs both lower with High Density thickeners at Ruashi

25. ` Questions ???