more newsBOLEO PILOT PLANT PROGRAM AT SGS LAKEFIELD RESEARCH SUCCESSFULLY COMPLETED
Baja Mining Corp. has successfully completed the Boleo pilot plant at SGS Lakefield Research Ltd. in Lakefield, Ont., Canada.
As was reported in the news issued in Stockwatch on Nov. 23, 2004, the pilot plant started on schedule on Tuesday, Nov. 16, 2004, treating a bulk sample of Boleo ore grading 1.85 per cent copper, 0.095 per cent cobalt, 0.59 per cent zinc, 4.3 per cent manganese and 7.9 per cent iron. The pilot plant flow sheet is essentially a miniature version of the expected full-scale circuit and comprises:
* attritioning of the ore with grinding of coarse ore particles to form an ore slurry;
* acid oxidation leaching of the ore with sulphuric acid in seawater;
* acid reduction leaching of the ore with sulphur dioxide and sulphuric acid in seawater;
* partial neutralization with limestone;
* counter current decantation (CCD) washing of the leach residue in thickeners (to separate the metal rich aqueous solution form the clayey waste);
* copper solvent extraction/electrowinning (SX/EW);
* iron removal by pH adjustment and oxidation with air (and polish with hydrogen peroxide);
* thickening of the iron residue (thickened residue goes to main CCD for washing); and
* direct solvent extraction technology (DSX) for selective recovery of cobalt and zinc (and small amounts of residual copper).
DSX technology is the property of Commonwealth Scientific Industrial Research Organization (CSIRO), Perth, Australia.
The pilot plant was shut down on Sunday, Nov. 28. The pilot plant equipment is currently being decommissioned and cleaned concurrent with analysis of all remaining samples (solids and liquids), and finalization of metallurgical balances and reporting.
A total of nearly two metric tonnes of ore were treated through the pilot plant.
SGS Lakefield and Bateman Engineering have jointly reported the summary findings from the pilot plant.
The pilot plant operated continuously for a total of 12 days in leaching, 11.5 days in CCD, 9.5 days in Copper SX/EW and nine days in cobalt and zinc SX, using DSX technology.
The oxidation, reduction leaching circuit gave excellent extractions of copper, cobalt and zinc. Copper extraction exceeded 90 per cent during pilot operation. Cobalt extraction was as high as 90 per cent. Zinc extraction was generally above 70 per cent. These numbers are indicative of the potential of the Boleo process to extract the three pay metals copper, cobalt, zinc. Final extractions will be calculated once all samples have been assayed and metallurgical balances completed.
The CCD circuit worked very well. The CCD was set up to simulate the use of the "high-rate" type of thickeners with recirculation of overflow solution to dilute the feed slurry prior to flocculation. This method of settling and washing was based on recommendations from bench scale testing by Outokumpu and Pocock Industrial, and proved to be highly effective. The leach residue settled quickly producing clear overflow solutions to advance to copper, cobalt and zinc recovery.
The copper SX/EW circuit performed very well. 15.5 kilograms of copper metal were electrowon from the solvent extraction strip solutions at high efficiency.
The iron removal circuit was designed to remove iron, aluminum and other impurities from the solution prior to recovery of cobalt and zinc using DSX technology from CSIRO. The iron removal circuit consistently produced very low concentrations of key impurities in solution with negligible losses of cobalt and zinc.
The CSIRO DSX circuit for cobalt and zinc recovery performed very well. The advantage of the DSX circuit for Boleo plant design is that cobalt and zinc are separated from manganese and magnesium in the Boleo leach solutions. In the Lakefield pilot plant, cobalt and zinc were recovered with high overall efficiency (plus-95 per cent) to produce a concentrated zinc sulphate solution (for production of zinc sulphate monohydrate crystals for sale) and a concentrated cobalt solution (for production of cobalt metal cathode).
After the normal commissioning problems with the pilot plant, the circuit behaved very well with stable consistent operation over many days.
Following receipt of all final assays, reports and metallurgical balances, the pilot plant data will be used by Bateman engineering in developing design data for the feasibility study.
Two further metallurgical tests will be performed on the products from the pilot plant.
Production of zinc sulphate monohydrate crystals. Zinc sulphate monohydrate will be recovered by evaporative crystallization of the zinc strip solution from the CSIRO DSX circuit.
Production of cobalt cathode. The cobalt strip solution from the DSX circuit containing cobalt along with small amounts of zinc and nickel will be treated by a further miniature SX/EW circuit to purify the cobalt solution for electrolysis as high-grade (plus-99.9 per cent) cobalt cathode. Conventional solvent extraction reagents and process steps have been selected for this purpose.
A further program of follow-up benchscale testwork is under way at Lakefield to obtain additional data for final feasibility study engineering.
Environmental testing of residues and solutions produced in the pilot plant program.
Characterization of high acid consuming (HAC) material from the Boleo site containing limestone and other alkali minerals. HAC material will be used as a low-cost neutralizing agent in the commercial Boleo plant.
Ore scrubbing and grinding testwork for developing final design for ore preparation circuit.
Testwork on oxidation and precipitation of iron prior to CSIRO DSX circuit to ensure maximum removal of iron with minimum treatment time and reagent consumption.
Leach tests on 24 samples of ore that were composited to form the pilot plant feed. These tests will be used to assess leach variability of the ore.
The successful completion of this pilot program is an important milestone in moving the Boleo project forward. For the first time Boleo ores have been treated in a continuous pilot plant program to leach, separate and recover pay metals in final commercial form.