URANIUM MILL’S TAILING

MANAGEMENT

Olympic Dam tailings, Australia

Uranium Fuel Cycle

Uranium Extraction process at Jaduguda

Source: R.M. Tripathi

Uranium Mill Tailings*The residual wastes

from milled ore after the uranium has been extracted, it may be solid and liquid (Barren liquor).

*May result from an acid leach process or an alkaline leach process.

*Tailings consist of slurries of sands and clay-like particles (called “slimes”).

Atlas Co. uranium mill tailings, Moab, Utah, USA - U.S. DOE Sep. 2010

Mill

’s W

ast

e

Solid Waste

Coarse Fraction

Fine Fraction

Barren LiquorEffluent

Treatment Plant

• Acid leaching– pH from 1.2 to 2.0– Na+, NH4+, SO4

-2, Cl- and PO4-3

– Dissolved solids up to 1 wt%– 20 to 7,500 pCi 226Ra/L– 2,000 to 22,000 pCi 230Th/L

• Alkaline leaching– pH from 10 to 10.5– CO3

-2, and HCO3

– Dissolved solids up to 10 wt%– 200 pCi 226Ra/L– Essentially no 230Th

TYPICAL CHARACTERISTICS OF LIQUIDS

Liquid (Barren

Liquior+Mine Water)

Decantated water from the Pond

Effluent Treatmen

t Plant

9

Tailings Processing & Effluent treatmentAt UCIL, Jaduguda

LeachResidue(solid effluent)

(40% by wt.)Cyclone

OF

To mine back filling

NeutralizationpH=10

Barren liquor from IX

Water from magnetite plant

lime

Settling tank

Flocculant(anionic, poly electro type)

Slimes + Mn Hydroxides

Overflow

Ba treatment forRA waste

BaCl2 solution

Ra, Ba sludgeTo SEP in plant

Cyclone

OF

To Tailings Dam

(60% by wt.) UF

(Liquid effluents)

Solid Mill’s Waste

Coarse FractionAfter neutralization, are used in underground for filling the mined out stopes.

Some time some binding materials (cement) are also used to provide mechanical strength.

Mine paste back fill will be practised in Tumllapalli mine.

Fine FractionContains mostly

slimes and are disposed in a tailing pond.

• Particle size range is 75 to 500 m.• Typically SiO2

• Contains <1 wt% complex silicates of Al, Fe, Mg, Ca, Na, K, Se, Mn, Ni, Mo, Zn, U and V.

• May also contain metallic oxides.• Contains 0.004 to 0.01 wt% U3O8.

• Contains 26 to 100 pCi 226Ra/g and 70 to 600 pCi 230Th/g.

TYPICAL CHARACTERISTICS OF SANDS

TYPICAL CHARACTERISTICS OF SLIMES

• Particle size range is 45 to 75 m.• Contains small amounts of SiO2.• May contain complex clay-like

silicates of Na, Ca, Mn, Mg, Al, and Fe.• May also contain metallic oxides.• The concentrations of U3O8 and

226Ra are twice that in the sands.• Contains 150 to 400 pCi 226Ra/g and

70 to 600 pCi 230Th/g.

Tailing Pond

Specially engineered impoundment system.

On three sides, it has high natural hills as barriers.

The embankment is designed in one side to accommodate the entire tailings for a very long period with no scope of its discharge into environment.

Decantation wells are planned to allow the flow of excess water.

Decanted effluent is treated further at effluent treatment plant and is brought to normal condition.

Functions of tailing ponds

Sedimentation of tailing solids;Final retention of tailing residue and precipitate sludges such as gypsum and iron bearing residue, radium- barium sulphate and other precipitates;

Acid neutralization, where the lime may be added;Radium removal, by addition of barium chloride;Heavy metal precipitate formation and sedimentation;Storage of seepage and runoff waters;Balancing of influent quality and quality;Storage prior to recycle of quantities of water for reuse in the process.

Uranium Mill’s Tailing Hazards

Potential environmental and health hazards

Gamma radiation;Contamination of food and water by dust and particulate matter;

Contamination of ground and surface waters by solutes originating from tailings, particularly heavy metals and radionuclides such as Radium 226;

Radon progeny – these are carcinogenic decay products of radon, a radioactive gas produced by radium;

Products of acid rock drainage in ground and surface waters.

Past practices for placement of uranium mill tailings

No effective containment,Topographic depressions,Within a custom built ring dyke,Returned to an underground mine,Low embankments,Returned to mined out pits,In a valley behind a dam or dyke,Into a deep lake or river.

Factors for Tailing Pond Selection

Required storage capacity for tailing and waste rock,

Site availability,

Hydrology and Hydrogeology,

Initial cost,

Ease of operations,

Geotechnical and Geological conditions,

Total engineering design.

Types of Tailing Ponds

Upstream tailings dam Centre line of the

dam moves downstream into the pond.

A small starter dam is placed at the extreme downstream point and the wall is progressively raised on the upstream side.Advantages Disadvantages

Low Cost. Dam wall is built on the top of the previously deposited unconsolidated slimes retained behind the wall.

Speed with which the dam can be raised by dyke increment.

Limiting height

Downstream tailing dam

Reverse of upstream method.

The centreline shifts downstream as the wall is raised and the dam is founded on the coarse tailing.

Advantages Disadvantages

Safer both insense of static and seismic loading.

Large amount of sand is required to raise the dam wall.

Centre-line tailings dam

Crest remain in the same horizontal position as the dam wall is raised.

Variation of that used in downstream dam.

Advantages Disadvantages

Require smaller volumes of sand fill to raise the crest to a given height.

Unstable slopes should not be developed temporarily.

Dam can be raised more quickly

Water gain and loss in a typical tailing dam

Structures used and proposed for tailing sites

Valley damRing dikeIn pitUnderground mineDeep lake and ocean etc.

*Each method will have its advantages or constraints.

*Selection will have to be approved by environmental agencies.

Decommissioning, Reclamation and covers

The objective of restoration includeStabilization of the surface to prevent wind and water erosion;

Provision of a cover to prevent or inhibit releases of contaminants (e.g. radon gas, radionuclides, sulphuric acids and metals);

Provision of an aesthetic appearance.

Environmental monitoring programme

will determine

Present levels of toxicants in the effluents;

Response of the environment to those effluents at the mine site and at various locations away from the point of discharge;

Pollution abatement measures necessary to comply with the standards.

Common parameters examined

1. Dissolved solids,

2. Suspended solids,

3. Dissolved oxygen,

4. Temperature,

5. Biochemical oxygen demand,

6. pH value,

7. Conductivity,

8. Cations and anions.

Monitoring of Tailing Impoundment Sites

Management of Uranium tailings wastes is a complex task, requiring a sound multi-disciplinary approach.

The problems include groundwater contamination, erosion, radon emanation and gamma radiation.

Evidence to date from remediation of old and modern sites, doesn’t demonstrate effective long term closure and safety.

Conclusions