Laterite Leach Tests

ANSTO Minerals Report C1206 to Lagoon Creek Resources – Westmoreland Deposits
achieving uranium extractions of 96.5-97.5% after 24 h. As very little uranium dissolution
occurred between 12 and 24 h, a 12 h leaching time would be sufficient. The rate of leaching
of uranium also responded to ORP, and an ORP of 550 mV is recommended. For these
conditions uranium extraction was 97% for both ores, with acid additions of only 18 and 14
kg/t for Junnagunna and Redtree, respectively. Predicted pyrolusite requirements were also
low at 3.0 kg/t for both ores.
The only conventional leach result conducted on the Jack sample, under base case conditions
shows that reagent requirements were less than half those for Redtree, but uranium extraction
was only 87% after 24 h.
4.5.3 Optimisation Tests on Junnagunna and Redtree
The optimisation tests on the Junnagunna and Redtree samples showed that:
• Varying the P80 grind sizes in the range 350 - 75 µm had negligible impact on
uranium extraction and acid addition. Finer grinding resulted in faster initial
uranium leaching kinetics, but a similar effect can was achieved by increasing the
ORP. Grinding to a P80 of 350 µm significantly reduced the rate of uranium
extraction up to about 12 h for Redtree. On this basis a P80 of 250 µm would
probably be selected to target a 12 h leach time.
• Leach pH over the range 1.3 – 1.7 had little impact on uranium recovery for
Junnagunna ore. At pH 2, extraction was reduced by 1% to ~ 96%. For the Redtree
sample, the 24 h extraction increased from 92% to 98% when the leaching pH was
decreased from pH 2.0 to pH 1.3. The pH also had an impact on the initial leaching
rate. The optimum pH for both ores was 1.5, or perhaps slightly lower for Redtree;
• Acid addition was low for both ores, ranging from 10-25 kg/t and 10-20 kg/t for
Junnagunna and Redtree, respectively, for all conditions examined;
• The pyrolusite requirement for both ores was ~3.0 kg/t for optimum leach
conditions. Note, the use of potassium permanganate and pyrolusite as oxidants
produced equivalent results;
• The uranium leaching rate increased with increasing temperatures from 30 °C to
50 °C. For both ores, leaching at 30 °C significantly decreased the extraction rate,
and to a lesser extent, the final extraction of uranium. The initial rate of leaching was
reduced at 40 °C, but extractions were quite similar to those at 50 °C after 12 h.
Although temperature has a significant effect on the initial extraction rate, there was
also a significant relative increase in the acid addition. The optimum temperature
appeared to be ~ 40 °C;
For both samples, similar final (24 h) uranium extraction results were achieved for leaching at
ORP levels of 500-550 mV. Uranium extraction decreased significantly when leaching at 450
mV. Addition of 1.0 g/L ferric ion at 500 mV had a slight impact on the rate of extraction, but
there was little difference after 12 h. A similar result was achieved by leaching at 550 mV,
and this approach would be preferred to adding iron. For both samples, there was a significant
increase in demand for oxidant to increase the ORP from 450 to 500 mV, but only a further
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