Studies on the recovery of uranium from low-grade ores in India

Investigations were carried out to utilize the available para-marginal and low-grade ores - chlorite schists, amphibolites, carbonate ores, clays and quartzites - analysing between 0.027 and 0.08% U3O8. In addition, tests were undertaken on the technical and economic feasibility of recovering uranium as a byproduct from the copper flotation tailings and phosphorites. Heap and bacterial leaching tests were conducted on quartz-chlorite schists from the Singhbhum district, Bihar, analysing about 0.03% U3O8. Studies also showed that the ores harbour active Ferrobacillus ferrooxidans. Studies on 10-mesh samples of amphibolites from Inderwa, Bihar, (0.08% U3O8) showed that only 32.8% recovery could be obtained by wet tabling and 85% by agitation leaching, while static leaching tests yielded 81% recovery in 24 hours of contact time. Similar tests on calcareous phyllites (0.05% U3O8) with 30 kg/t Na2CO3 and 8 kg/t NaHCO3 yielded 86% uranium leachability at ambient temperature. Biogenic uraniferous clay from Udaisagar (0.029% U3O8) yielded 43.3% uranium recovery using 1000 l/t of neutral water for 6 h. Percolation leaching tests were conducted with hard quartzites (0.06% U3O8), and the results showed that 81% uranium could be recovered in 24 days. Although preliminary ore dressing studies on tailings obtained from the copper flotation (0.013% U3O8) at Surda yielded a concentrate analysing 0.063% U3O8 at 66% recovery, recent tests on the tailings from the copper concentrator indicated only 48% recovery at a grade of 0.112% owing to decrease in the feed grade. Studies on the utilization of large-capacity gravity machines and selective mining of uranium-rich copper lodes may render this source economic. Preliminary studies on a phosphorite sample containing 22.0% P2O5 and 0.04% U3O8 from the Mussorie area in Uttar Pradesh on calcination followed by scrubbing yielded a sand enriched in P2O5 values (33.7% P2O5 at 92.5% recovery) but not in U3O8 values. Bulk tests conducted on large tonnages of sample confirmed the data obtained in the laboratory tests