DOWNSTREAM PROCESSING OPTIONS FOR NICKEL LATERITE HEAP LEACH LIQUORS By
Boyd Willis Aker Kvaerner Australia Pty Ltd Presented by Boyd Willis
[email protected]
CONTENTS
ABSTRACT ............................................................................................................................... 2 1.
INTRODUCTION ............................................................................................................... 2
2.
ESTABLISHED FLOWSHEETS ........................................................................................ 2 2.1. 2.2.
3.
MIXED HYDROXIDE PRECIPITATION (MHP) ROUTE MIXED SULPHIDE PRECIPITATION (MSP) ROUTE
2 9
CONCEPTUAL HYBRID FLOWSHEETS........................................................................ 15 3.1. 3.2. 3.3. 3.4.
NICKEL AND COBALT RECOVERY BY MOLECULAR RECOGNITION TECHNOLOGY (MRT) MIXED SULPHIDE PRECIPITATION WITH IRON REMOVAL BY MOLECULAR RECOGNITION TECHNOLOGY (MRT) MIXED SULPHIDE PRECIPITATION WITH IRON REMOVAL BY ION EXCHANGE (IX) MIXED SULPHIDE PRECIPITATION WITH IRON REMOVAL BY RESIN-IN-PULP (RIP)
15 18 20 22
4.
COMPARISON OF FLOWSHEET STRENGTHS AND WEAKNESSES......................... 25
5.
ACKNOWLEDGEMENTS................................................................................................ 26
6.
REFERENCES ................................................................................................................ 26
ABSTRACT Growing worldwide interest in the application of heap leaching technology to nickel laterite ores heralds a need to explore compatible nickel recovery flowsheets. Alternative approaches to downstream processing of nickel laterite heap leach liquors are described and reviewed. Block flowsheets for established and conceptual processes are presented and each flowsheet is assessed in terms of strengths, weaknesses and product quality. The impact of ore type and grade on process selection is examined. Considerations related to project location and infrastructure needs are also discussed. Generic examples are given where appropriate. 1. INTRODUCTION The arrival of nickel laterite heap leaching on the world stage, largely through the endeavours of European Nickel in Turkey, has generated much interest. As more and more projects assess the amenability of their ores to heap leaching, it has become evident, as it did with high pressure acid leaching (HPAL), that different ore bodies and locations lend themselves to different downstream recovery processes. While generally speaking any downstream nickel recovery flowsheet can be adapted to any nickel laterite heap leach, there will always be an option which optimises the project economics. In recent years there has been substantial refinement of process flowsheets for the downstream recovery of nickel from HPAL discharge slurries. However, the same cannot be said for heap leach liquors. The pregnant leach solution (PLS) obtained from a nickel laterite heap leach exhibits some significant differences to a HPAL discharge slurry. HPAL produces a hot slurry, at 20-25% solids, containing typically 4-6 g/L nickel, 40-60 g/L sulphuric acid, 50°C is favoured to facilitate high recoveries of nickel and cobalt. Operation at low or ambient temperature is not recommended as dissolution extents are low. By maintaining a terminal sulphuric acid concentration after recycle leaching of >20 g/L, nickel and cobalt recoveries from the precipitates of 95-100% can be achieved. Significant quantities of any iron, aluminium and other hydroxides present also re-dissolve. Process Description
The solids produced in 2nd stage iron removal and 2nd stage nickel-cobalt precipitation are thickened and directed to the Recycle Leach, where they are contacted with incoming heap leach PLS. Typically 1 or 2 tanks in series are used, operating at >50°C, with between 60 and 120 minutes combined residence time. The discharge stream is forwarded to iron removal. The recycle streams increase the hydraulic throughput of the downstream processes. 2.1.3.
Iron Removal
The function of iron removal is to neutralise excess acid in the heap leach PLS and to remove iron and aluminium from solution prior to nickel and cobalt precipitation. Chemistry
Iron, as Fe(III), can be removed from leach liquors to a residual concentration of
