pH advanced process control solution for Impala BMR first stage high pressure acid-oxygen leach

1. pH advanced process control solution for Impala BMR first stage high pressure acid-oxygen leach Abdullah Khan 26 February 2009 Hydrometallurgy Conference Muldersdrift

2. Agenda • Company Overview • BMR Process Flow • Frameworks - I & C Systems • Advanced pH Controller

3. Company Overview • Impala Platinum second largest platinum producer in world • Produce 2.0 million ounces of platinum annually • Produce copper, nickel and cobalt as by-product • Generate annual income of R 1.5 billion from base metals • General platinum process overview:

4. BMR Process Flowsheet MATTE GRINDING MATTE FROM MINPRO NICKEL LEACH COPPER LEACH PGM CONC LEACHING PGM CONC DRYING DESPATCH TO PMR NICKEL PURIFICATION COPPER PURIFICATION COPPER ELECTROWINNING COPPER PRODUCT NICKEL REDUCTION COBALT STRIPPING COBALT PURIFICATION COBALT PRODUCTION SAMPLE QA PACKING NICKEL POWDER WASHING/DRYING AMM SULPH PRODUCTION SAMPLE QA PACKING BRIQUETTING SINTERING SAMPLE QA PACKING SALES

5. Frameworks - Information & Control Systems

6. Hardware APC Business Strategy Defines IT Architecture Software MES Network LIMS Data Supports Procedures Human Human Human Source: Butler M, ISM - USB

7. Data Information Knowledge Wisdom Raw facts Organized collection of facts Awareness/ understanding of set of info and how it can be applied Judicious application of knowledge Human

8. Advanced pH Controller in First Stage Leach - Feedback

9. Process Description

10. The Process Problem • Fe is an impurity. Sometimes >1% in matte. Needs to be removed in first stage otherwise continues through PGM circuit causing filtration problems • Ni (+/- 47% in matte) extracted in first stage process • Need to ensure high Fe and Ni extraction efficiencies • Improvement of PGM grade • How do we achieve this? • Control pH

11. pH Advanced Controller Principles • Stabilise pH to improve leaching efficiency of Fe and Ni – better quality of PGM concentrate • High pressure acid leach has complex reaction kinetics • On-line pH sampling • Simplify control approach. Manipulate acid addition to compensate for: • Pulp density changes, Product feed rate changes & • pH response measurements • Advanced controller based on a hybrid of fuzzy logic technology and fundamental principles

12. APC Design • Disturbance variables: • matte composition, spent electrolyte solution composition, pulp feed rate • State variables: • pulp density, Cu in solution • Adjustable variable: • spent electrolyte flow rate • Target variable: • ph in first compartment

13. Sampling and Measurement

14. PD required in autoclave pH setpoint: 1.8 – 2 “Measured Disturbances” + + - PD from TK2102 FF Control FB Control Pulp feed rate - Spent electrolyte flow rate First Stage Leach Process Pulp density from TK2102 Process output: pH Pulp feed rate to autoclave APC Solution

15. APC Performance

16. APC Results • PGM concentrate grade is better i.e. Less Fe and Ni slippage • Performance analysis conducted in March 2007: • pH variation reduced from 1.2 to 0.7 (an improvement of 40% in pH stability) • Ni extraction efficiency increased by 0.5% to 91.7% • Fe extraction efficiency increased by 3.3% to 88.5% • Increase of PGM grade by 1.4%

17. Low throughputs: pH control not as good which presents opportunity for controller improvement Change management: People Training Work Procedures Controller and process performance monitoring SLA – controller maintenance and performance audits APC - Challenges

18. APC – Challenges Overcome

19. Thank you