Dutwa Metallurgy

The table and charts below show the acid consumption and nickel and cobalt extractions from “bottle roll” leach tests conducted by Mintek of South Africa on samples from African Eagle’s Dutwa nickel laterite, Tanzania.

Ten 500g samples, five from diamond drill cores and five from reverse circulation cuttings were each placed in glass bottles with two litres of dilute sulphuric acid and agitated continuously by rolling on rotating rollers. Mintek completed the tests in mid-February 2009 after 82 days rolling. The bottle roll tests levelled off after 60 days, which is similar to test work done on other laterite ores that subsequently gave heap leach cycles of less than 200 days although this has not yet been demonstrated.

The nickel extractions in the table were based on assays of the samples prior to the test and of the solid residues at the end of the test. Final results were all between 70-90% averaging 83%. Extractions calculated from the daily assays of the liquid leachate, shown in the charts, were higher, at 80-95%, but are generally less reliable. The acid consumptions, averaging 209kg/t, are extremely low compared with other nickel laterite ores. The solids-based cobalt extractions were mostly in the range 70 to 85%.

Bottle Roll Results
	DH1	DH4	DH6	DH7	DH8	RC25	RC30	RC36	RC55	RC71	Average
Acid kg/t	352	196	233	114	200	159	207	304	190	138	209
Ni%	85	80	89	78	91	88	71	88	86	75	83
Co%	69	71	77	55	85	76	18	77	86	73	69

Mintek used X-ray Diffraction (XRD), and scanning electron microscope (SEM) backscattered electron images to investigate the mineralogy of the drill core and chips. Sixteen samples of drill core and five samples of reverse circulation (RC) cuttings were submitted for XRD analysis. The five RC samples and five composited drill core samples were investigated by SEM.

The results, shown in the diagrams below, revealed two broad classes of material: a dominant class composed largely of silica (quartz) and a mixed class. The latter also contains silica, together with variable amounts of the iron-chromium oxides magnetite and chromite (described as “spinel” in the legend); the hydrated iron oxide goethite; “manganese wad”, described as Phase X in the legend, in which manganese, nickel, cobalt and other metals replace some of the iron in amorphous goethite; and small quantities of serpentine and clays.

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