Soluble Metal Recovery Improvement Using High Density Thickeners

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

Introduction n n ` n Ruashi is a Copper/Cobalt mine in the DRC Circuit overview: Leach-CCD-SX-EW Copper recovery is critical in the CCD circuit Lab & CCD simulations to optimise recovery 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

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

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

Optimal Flocculant Dosage ` Optimum = 50 g/t

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

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

Rheology ` 60 Pa at 59% Solids

` CCD Simulations

CCD Simulations Variables used in base case simulation ` Wash Ratio 1. 6 U/F Suspended Solids Concentration (wt%) Feed Suspended Solids Concentration (wt%) Soluble Cu Recovery (%) 55 30 +99

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 l Per thickener cost is similar – HD diameter smaller 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 n ` n Higher tank sidewall depth Steeper tank floor slope Higher rake mechanism torque Rake mechanism – Pickets Thickener discharge cylinder

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

Questions ? ? ? `