1 Gravity Concentration at Ashanti Goldfields BIOX Plant Obuasi Mine; Ghana, W. Africa
2 CONTENTS1. Introduction Knelson Concentrator - Overview Obuasi STP-Biox Plant Flowsheet 2. Testwork Results from lab scale testing 3. Construction and Installation Materials of Construction 4. Circuit Metallurgy Operating parameters of the circuit Impact of the Knelson Concentrator 5. Summary
4 On-site Lab Test WorkObjective: To determine the presence of free gold in the STP Biox circuit.- free gold- easily visible1. Three Streams Tested a) CCD Thickener #5 U/F b) Biox-CIL Tailings c) Final Tailings (from flotation) 2. Considerations severe corrosion of the lab test machine corrosive nature of the Biox process (pH )- fine free gold - visible under the microscope- flat gold flakes - easily visible - flat shape attributed to grinding
5 Lab Test Work Summary1. Photomicrographs and visual observations indicated the presence of free gold in all of the streams tested Free gold passed through the CIL circuit without complete leaching Internal work by Ashanti indicated that free gold is liberated in the Biox Process % of the liberated gold particles are <20 micron. 5. Any installation of a Knelson Concentrator in the Biox/CCD circuit would have to address the corrosive nature of this slurry (pH ).
7 Modifications to the Knelson Concentrator Materials of Construction Evaluated a) Hastelloy C b) Incolloy c) Stainless Steel 904L d) Stainless Steel 304L - Ashanti indicated that 304L had performed very well for other equpiment located in that part of the plant The other alloys would have at least doubled the cost of manufacture compared to the standard unit.
8 Materials of Construction General Assembly Stainless Steel (304L) - Tail. Launder Linatex Rubber Lined - Motor Cover - General Assembly - Upper & Lower Frame Assemblies - Conc. LaundersElectroless Nickel Plated - Upper & Lower Bearing Exteriors - Drive Sheave/Bushing
9 Operating ParametersKnelson Concentrator Hourly Tonnage tonnesPulp Density of Knelson Feed % (w/w)Temperature of Knelson Feed 30oCSlurry pHSize distribution of Knelson Feed 90% passing 45 micronsConcentrating Cycle Time 3 hours/cycleKnelson Fluidization Flow (USgpm) 130 gpm
10 Process Improvements Plant Au Recovery Prior to KC Installation 87% Plant Au Recovery After KC Installation %Percentage of Total Gold Recovered by KC %CIL Tails Grade Prior to KC Installation g-Au/tCIL Tails Grade After KC Installation g-Au/t
11 Knelson Concentrator Installation at AGC Obausi Mine; Ghana, W. Africa
12 SUMMARY & CONCLUSIONS1. Lab testing identified free gold present in the CCD circuit, CIL tails and final tails Free gold passed through the CIL circuit without complete leaching Decision to install a Knelson Concentrator in the CCD circuit after the Biox process The materials of construction were modified to 304L stainless steel to withstand the severely corrosive nature of the slurry Installation was extremely successful with significant improvents to gold recovery.