BULK TESTS

Following the encouraging results obtained in the laboratory, bulk tests were conducted at two of the mine sites, Umra and Chhinjra. Uranium was recovered from the pregnant liquor by an ion-exchange method using De-acidite FF-530, suitably arranged in 4 FRP, fixed-bed columns.

Uranium from the chloride eluate was then precipitated using NaOH. Figures 4 and 5 show the plant layouts. Results of these tests are shown in Table VII [11].

5. DISCUSSION

While extraction methods for treating large deposits of high-grade ore are well known, small high-grade deposits and large but low-grade deposits require considerable laboratory and pilot-plant experience before finalizing the process design. Diverse techniques are needed to exploit ores varying in mineralogical complexion and physical characteristics. Any process designed for a given ore type may not hold good for another and mineralogical variations even in the same lode are not uncommon. Since the exploitation of any deposit depends on its economic viability, it is imperative that para-marginal and low-grade ores are treated by cheaper techniques requiring lower capital input.

Physical beneficiation of low-grade ores is being attempted in several countries. Although heavy-media separation, jigging, tabling, flotation and radiometric lump or car sorting are carried out both at the pilot-plant level and in large-capacity mills, these methods have not found favour since size reduction becomes unavoidable for preconcentration. This, together with the considerable loss of uranium values in the tailings, which is too high to be neglected, renders these techniques unsuitable. Further, if the cost of uranium increases as expected, ore dressing steps, due to lower overall recoveries, become more and more uneconomic. However, ore dressing steps can be gainfully used for byproduct recovery from multi-metallic or non-metallic ores, using selective mining if necessary.

Barring a few isolated cases, uranium ores are primarily treated by the hot agitation leaching technique. The recoveries by this method are usually of the order of 90% and uranium from the pregnant liquors is extracted either by resin ion exchange or by solvent extraction techniques.

Although almost all the present production is obtained by this technique, the capital required in

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FIG. 5. Layout of the Kulu heap leaching plant - SE-NW elevation. Capacity 25 t/d.

Level I - water tank, ore yard, jaw crusher, acid tank; level 2 — roll crusher; level 3 - crushed ore yard; level 4 - leaching tank; levels - leach liquor lank, NaOH lank, Na2CO3/NaCl tank; lévelo working platform for extraction unit; level 7 -resin column/countercurrent unit; level S - precipitation unit, filtration unit; level 9 - barren liquor tank and pump.

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1 68 JAYARAM et al.

the main process and also in the accessory supports, such as acid plants, oxidant grinding mills, steam raising equipment, etc., renders the process uneconomic for para-marginal ores. Another limitation is the relatively high boundary imposed on the cut-off grade, due to the high mining, grinding and filtration costs. Unless research and development work is increased to design new equipment and to reduce the process cost (such as solvent in pulp or resin in pulp), low-grade ores cannot be treated by this conventional process.

Several countries are actively engaged in adopting heap leaching, bacterial leaching and solution mining techniques for extracting uranium from low-grade ores. With rising reagent and labour costs this method holds promise for the exploitation of small, pockety, high-grade deposits and large low-grade deposits, since it has the advantage of being simple and cheap. The limitations, however, are the prolonged leaching time, comparatively lower recovery of 50 to 80% and the high mining cost. Further, it may be necessary to crush the ore to about 5 mm size for obtaining competitive recoveries from the disseminated type of ores. Thus heap leaching, bacterial leaching and solution mining techniques are not yet developed as independent process techniques, and are riddled with many plant engineering problems.

Bacterial leaching, although encouraging, is not an end in itself. Careful experimentation and interpretation is required, since all the ore may not harbour indigenous bacteria and inoculation of cultures in large ore dumps may offset the cost saved on the leachants, etc. The utilization of barren liquor, attempted in bulk tests carried out in India, has proved that it is not necessary to seed bacteria or feed the nutrients continuously. It would be enough to hasten the reaction by using the nutrients in the initial batch and to use the ion-exchange barrens in subsequent cycles.

Large para-marginal deposits which do not justify a conventional plant can be treated by a judicious process mix of the different techniques.

6. RESEARCH ORIENTATIONS

Detailed investigations into the mineralogical, chemical and locational aspects of each individual occurrence and a judicious process mix may render the para-marginal and low-grade ores amenable to exploitation at competitive prices. A rough cost analysis of different unit operations shows that about 20% of the extraction cost and 30-40% of the direct cost is accounted for by milling and leaching respectively. The other major costs are for filtration and waste disposal. Research is, therefore, required to minimize these costs.

The mills as are currently operated and designed are bulky and heavy, and consume a dis-proportionately large portion of the power when compared to the actual power required for grinding the ore itself. Added to this is the imperfect classification of the mill discharge owing to the variation in the mineralogical characteristics of the diverse ore-gangue complexes. The need to study the behaviour of fine particles (slimes) is to be kept in view. Studies on flocculation, ore agglomeration, gravity treatment and flotation of ultrafines may enable the utilization of low-grade ores. Similarly, studies to develop and perfect large-capacity machines and to reduce reagent consumption and increase specific ore particle/reagent interaction are necessary.

In the case of dump leaching, investigations to reduce leaching time and return of the tailings to the mine (as backfill) are necessary before this method could be accepted in full.

The tailings obtained by chemical extraction methods would leave enough free acid and other toxic products. Development of cheap reagents to fix these poisonous products need be achieved early. For this also, the role of anaerobic and heterotrophic bacteria needs understanding.

ACKNOWLEDGEMENTS

We are grateful to Dr. G.R. Udas, Director, Atomic Minerals Division, for the encouragement.

Thanks are also due to Dr. Т.К. Bhattacharya and his colleagues for mineral analysis and to

IAEA-AG/33-11 1 69 Shri B.N. Tikoo and his associates for chemical analysis. Devoted work conducted by

Shri S.C. Kulshrestha, Dr. M.C. Bhurat, Shri R.N. Sankaran, Shri S.R. Shivananda, Shri A.B. Duddalwar, Shri A.K. Mathur, Shri B.D. Chetterji and Shri V.K. Sharma is acknowledged with thanks. We are also thankful to the supporting workers in the laboratory and field, without whose co-operation and untiring work this would not have been possible.

REFERENCES

[1] INTERNATIONAL ATOMIC ENERGY AGENCY, Uranium fuel of the future: The formation of uranium deposits, IAEA Bulletin 16 20 (1974).

[2] CAMERON, J., IAEA Bulletin 15 5(1973) 1 0 - 1 3 .

[3] BHURAT, M.C., et al., "Some results of microbial leaching of uranium ore samples from Narwapahar, Bhatin and Keruadungri, Singhbhum dt., Bihar", Symp. Bacterial Leaching, N.M.L., Jamshedpur, India (1971).

[4] JAY ARAM, K.M.V., et al., "Bacterial leaching of uraniferous chlorite schist from Narwapahar, and Bhatin mines", Symp. Uranium in India, Jaduguda (1971).

[5] DUDULWAR, A.B., Some Beneficiation and Leaching Tests on the Low Grade Uraniferous Amphibolites from Inderwa, Hazaribagh dt., Bihar, Unpub. Rep., Dept. Atomic Energy, India (1968).

[6J JAYARAM, K.M.V., DWIVEDY, K.K., BHURAT, M.C., KULSHRESTHA, S.G., "A study of the influence of microflora on the genesis of uranium occurrences at Udaisagar, Udaipur District, Rajasthan", Formation of Uranium Ore Deposits (Proc. Symp. Athens, 1974), IAEA, Vienna (1974) 8 9 - 9 8 .

[7] CHATTERJI, B.D., et al., "Results of some beneficiation and lixiviation tests on medium grade uranium ore in quartzite from Chhinjra, Kulu dt., H.P.", Proc. 1 N.S.A. 36A 6 (1970) 3 8 4 - 9 1 .

[8] RAM ACH AR, T.M., SINHA, R.P., Recovery of Uraniferous Concentrate out of Copper Ore Flotation Tailings from Surda Mine, Singhbhum dt., Bihar, Unpub. Rep., Dept. Atomic Energy, India (1969).

[9] RAMBABU, Ch., MAJUNDAR, K.K., Phosphorite Deposits in India and Their Beneficiation, Unpub. Rep.

BARCO972).

[10] SHIVANANDA, S.R., et al., Interim Report on a Sample of Phosphorite from Mussorie dt., U.P., Unpub.

Rep., Dept. Atomic Energy, India (1972).

[11] JAYARAM, K.M.V., KULSHRESTHA, S.C., "Some results of lixiviation tests on bulk uraniferous quartzite ore under field conditions at Chhinjra, Kulu dt., H.P.", Proc. 1 N.S.A. 36A S (1970).

DISCUSSION

T.S. ARY: You mention that in one case you had a shale with 0.02% U3O8 and the uranium was leached by a bacterial process from the black shales and remobilized and deposited in the clay.

What evidence do you have of this remobilization and redeposition?

K.M.V. JAYARAM: A paper on this topic has been published by the IAEA.1 The main evidence is as follows: 1. The uranium available in the black shales surrounding the fault zone is depleted compared to the uranium in the general black shales in the area. 2. The

hydro-geological studies using tracer technology have shown a migration of the waters, hydrological waters, from the black shales into the fault zone. 3. The fault zone itself contains clay which is a neutral exchanger in itself for uranium. There is a profuse growth of Desulfovibrio desulphuricans, which is a reducing bacterium in this zone, and a profuse growth of the oxidating bacteria in the black shale zone. Other evidence is that there is a seasonal fluctuation of uranium content in the wells around and in the shaft. During the rainy season we find that the water contains a little more uranium than during the dry season. About 40—50% of the uranium is water-soluble. When clay is put into water and left there for an hour, 50% of the uranium is extracted.

JAYARAM, K.M.V., DWIVEDY, K.K., BHURAT, M.C., KULSHRESTHA, S.G., "A study of the influence of microflora on the genesis of uranium occurrences at Udaisagar, Udaipur district, Rajasthan", Formation of Uranium Ore Deposits (Proc. Symp. Athens, 1974), IAEA, Vienna (1974) 89.

] 7 0 JAYARAM et al.

T.S. ARY: I should like to point out the different outlook of the mining man and the milling man. In the USA we have a lot of promotional activity with respect to our minerals and our uranium boom, our silver boom and what have you, and it seems to me that the promotors are always trying to build mills before they find an orebody. In this particular case I would suggest that more time be spent on geology and exploration work until you find an orebody that it is worthwhile building a mill on. I do not know how extensive the geological and exploration effort has been, but my information is that there is a great deal still to be done in India. This is surely a more important matter than how to handle a 0.02% ore and whether the miners should mine it and whether you should leach it in place.

K.M.V. JAYARAM: Certainly one would like to discover more and much richer deposits.

I think it is in an IAEA publication where the annual mean discovery rate is put at only 65 000 tonnes. Of late, but for the recent Australian finds, I do not think that we have come across deposits that are really rich. Generally, in the base metal industry, we find that the grades do go down and, after all, mineral wealth is a wasting asset. One day we shall have to take up low-grade ore utilization. Low-grade utilization and cost structure differ from place to place.

In geological terms, there are areas which are completely devoid of a particular metal. For instance, the USA is rich in uranium but lacking in certain other metals such as manganese. In India there are many metallogenic provinces that are rich in thorium but poor in uranium. We are doing our best and some recent finds are encouraging. We have a large area to investigate and in the coming two decades or so, considering the forecasts for uranium supply and demand, we shall have to go down in grade. For instance, an eight-step lowering in copper grades has taken place even in the USA. Taking 0.25% U3O8 as the grade of ore which was treated in the USA several years ago and assuming an eight-step lowering by analogy with copper, we come to an ore grade of 0.02 or 0.03% U3O8.

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