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

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

` 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

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

` Different Thickener Technologies

` Counter Current Decantation (CCD)

` Lab Simulations

` 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

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

` Optimal Flocculant Dosage Optimum = 50g/t

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

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

` Rheology 60 Pa at 59% Solids

` CCD Simulations

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

` CCD Wash Recovery

` Sensitivity to Wash Ratio

` Sensitivity to Underflow % Solids

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

` High Density vs High Rate

` 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

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

` 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

` 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

` Questions ???