Atmospheric Leaching > Pilot Plant Results

Skye Resources recently announced the successful completion of the pilot plant testing of its proprietary Sulphation Atmospheric Leach (“SAL”) Process. The testing was carried out by SGS Minerals Services in Lakefield, Ontario, Canada. The SGS final report on the last phase of piloting was received on March 17, 2006. Ten continuous test campaigns were completed between February and December 2005 using bulk samples of nickel and cobalt bearing laterites taken from Skye’s Fenix Project exploration license areas in Guatemala in 2004 and 2005.

The flowsheet tested consists of the following unit processes:

• Direct sulphation of limonite by reaction with concentrated sulphuric acid;
• Mixing of sulphated limonite with crushed saprolite and water, followed by grinding in a ball mill to produce a leach slurry (the limonite sulphation and saprolite grinding steps constituting leach slurry preparation – LSP);
• Atmospheric leaching (AL) in a series of agitated tanks at 90-100 ^oC and, importantly, atmospheric pressure;
• Primary iron removal (PIR) by ground limestone addition to the leach slurry;
• Counter-current decantation (CCD) to separate washed leach residue from pregnant liquor containing dissolved nickel and cobalt;
• Secondary iron removal (SIR) with ground limestone and air/hydrogen peroxide to precipitate all iron, aluminum and chromium from the pregnant liquor and separation of the solids in a thickener;
• Mixed hydroxide precipitation (MHP) with magnesia, followed by thickening and filtration, to produce an intermediate mixed nickel/cobalt hydroxide for sale to nickel/cobalt refiners;
• Scavenger precipitation (SP) with lime slurry, followed by thickening, to recover remaining nickel and cobalt;
• Manganese removal (MR) with lime slurry and air followed by thickening to produce barren liquor containing only magnesium sulphate.

The capacity of the pilot plant was 160-240 kg/day limonite plus saprolite (dry basis), except for the leach slurry preparation circuit, which had a capacity of 2,300 kg/day limonite plus saprolite. The LSP circuit was operated in 5 to 6 hour campaigns periodically to provide leach slurry for the leaching and downstream unit operations, which operated 24 hours/day.

The first nine campaigns were of five days duration. In six of these campaigns, the “front end” circuit (LSP, AL, PIR and CCD) was tested, while in three campaigns, the “back end” circuit (SIR, MHP, SP, and MR) was tested. The final campaign (campaign “PP11”) was run for ten days and encompassed the entire flowsheet. The byproduct streams (SIR and SP thickener underflows) were releached and recycled to the AL circuit during this campaign.

The proprietary SAL Process consists of the front end circuit only (see attached block flow diagram). The back end circuit for MHP production is a commercially proven process operated by others and was chosen only to show that a good quality nickel/cobalt intermediate product could be produced from leach liquor generated by the SAL Process. It is likely that other commercially proven processes could be used alternatively to recover nickel and cobalt from SAL pregnant liquor.

There were no instances of process-related downtime during the test campaigns, demonstrating the simplicity and robustness of the SAL Process. Key data and results from the 10-day integrated campaign may be summarized as follows:

The SGS Minerals Services Final Report stated, “Based on the smooth operation of the latter 5 days of the integrated PP11 campaign and the virtually zero downtime of all unit processes, it can be concluded that the SAL process flowsheet appears fundamentally sound.”

A great deal of data was collected to establish process design criteria. Skye believes that the next steps towards commercialization of the SAL Process include scale-up of the key Leach Slurry Preparation unit processes and extended operation of a larger size pilot or “demonstration” plant at a project site. 

The SAL Process is the subject of US Patent Application No. US 2006/0002835 A1 and PCT Patent Application No. WO 2006/000098 A1, both published on Jan. 5, 2006. The claimed priority date is June 28, 2004, the filing date of a related provisional US application.

Given the positive results from the pilot plant program, Skye initiated and completed a Preliminary Assessment being undertaken primarily by Hatch Ltd., to determine the approximate capital and operating costs of a proposed 50 million pound Ni per year expansion of the Fenix ferronickel smelter, itself the subject of a Feasibility Study. Both studies were completed in the third quarter of 2006. The Preliminary Assessment initially compared the SAL Process to the High Pressure Acid Leach (HPAL) Process, and the HPAL Process was selected for detailed cost estimation. Either option would allow exploitation of the limonite resources associated with the Fenix project.

SAL Process Block Flow Diagram