Laterite Leach Tests

ANSTO Minerals Report C1206 to Lagoon Creek Resources – Westmoreland Deposits iii
• 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. 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 0.5 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 small addition
was required to achieve 550 mV. The oxidant demand for both samples was very
similar for both samples. The optimum ORP is considered to be 550 mV;
• For both the Junnagunna and Redtree ores, sizing of leach residues from base case
conditions showed that high uranium extractions were obtained for all size fractions,
with extraction decreasing slightly in the three coarsest fractions (> 150 µm).
Residue grades were greatest, marginally, for the three finest fractions (< 53 µm).
The limited tests carried out on the Jack ore sample showed that:
• Under base conditions, the extraction of uranium from the Jack ore sample was 87%,
considerably less than the dilute leach result of 97%, and significantly less than the
96-97% extraction from the other two samples under base case conditions. This
result could be due to the very low ferric ion concentration (0.2 g/L) in the Jack
leach liquor;