- PDF Free Download

Size: px

Start display at page:

Download ""

Darcy Pope
6 years ago
Views:

1 Membrane Processes for the Treatment of UMM Radwastes M. Isabel F. Paiva, Ph.D Nuclear and Technological Institute Department of Radiological Protection and Nuclear Safety IAEA Technical Meeting on Uranium Exploration, Mining, Production, Mine Remediation and Environmental Issues 1-5 October, 2007, Swakopmund, Namibia,

3 URANIUM EXPLORATION IN PORTUGAL Main mine: Urgeiriça U Mine Deposits of U and Ra discovered in 1912 Location North of Portugal Geology Hercynian granitic and perigranitic areas Industrial activities -started 1955/1961 Type of mining- Undergroung, ISL, HL Chemical facility acid leaching

4 Urgeiri Urgeiriça U Mine ended up its production around 1993 Until the end of 1999, between 60 and 100 small mines were still explored : heap leaching of low grade ores and ISL of richer ores Ion Ion-Exchange resins containing resulting liquors from the ILS with H 2 SO 4 were transported by trucks to the milling facilities for chemical treatment.

5 Wastes from UMM Process Mining wastes large quantities of water from drilling, drainage from backfill operations, washing water, seepage from heap leaching, treated before discharge/recycle back to the process Milling wastes ground solid residues and associated liquids (with all the chemicals and heavy metals): Slimes - the finer particles in the tailings (<75µ); clays, silts, etc. Sands - the heavier, coarser particles Large volumes of slurries Transported to the impoundment basins; solid particles settled out and the effluent is treated for removal of contaminants before discharge into a settling pond or to the tailings

6 Main UMM Liquid Wastes Characteristics and Origins Barren solutions from milling and associated effluents from tailings. Are acidic or alkaline liquors from which U or Th were removed Generation points: raffinates or aqueous barrens from solvent extraction; eluates from the ion- exchange; overflow from tailings basin,acidic seepage and run-off from tailings Acid leaching solutions contaminated with sulphuric acid, sulphates, nitrates, heavy metals, organic solvents and amines, chlorides and radionuclides

7 Urgeiricas mining and milling facilities Traditional Process for the Treatment of the acidic mill effluents Liquid Effluent treatment facility: automatic hidrat. unit; 3 reactors in cascade for the effluent neutralization; decantation ponds for the settling of the sludge Purification steps: neutralization of sulphuric acid with CaO up tp ph 10; pp of some sulphates and heavy metals, partial removal of 226 Ra by pp. with 25 mg/l BaCl 2, in the presence of sulphates excess; removal of amines by adsorption on pp. solids Insolubilization of dissolved radium by coprecipitation or syncristalisation of the radium ions with barium sulphate

8 Considerations about the Conventional Treatment Process Effective removal of radium and other heavy metals in order to allow effluent discharge into the environment but at a very high price! Origins large volumes of gypsum in need of large settling ponds (retention time of 10 days for 80% Ra removal)

9 Iron precipitates Iron precipitates increase the weight of the tailings and sulphates affect containment structures. Sulphide minerals present and bacterial oxidation increases mobility of the contaminants in the seepage Ba(Ra)SO Ba(Ra)SO 4 sludges have high conc of 226 Ra remain insoluble in the settling ponds BUT if the liquid flowing over it changes, resolubilization or resuspension of the precipitate can occur Aqueous stream produced Aqueous stream produced is not adequate to be recycled back as water process

11 SELECTION OF A TREATMENT PROCESS Chemical properties Chemical properties ph, chemical components, toxicity, speciation, oxygen demand, presence of phases Physical properties Physical properties electrical conductivity, turbidity, surface tension, density, particles size, colloids Radiological properties

12 PERFORMANCE OF A TREATMENT PROCESS Volume Reduction Factor (VRF) Decontamination Factor (DF) Percentage of Removal (%)

13 Some of the Main Objectives of a Radwaste Treatment Management Program To prevent To prevent generation of wastes whenever possible by using clean technologies To minimize To minimize the number of waste streams by integrating all waste management aspects of the design stage of the plants, processes and products To produce To produce wastes that are adequate for disposal To recycle water back to the process

14 ADVANCED PROCESSES FOR THE TREATMENT OF LOW LEVEL LIQUID WASTES Example: Membrane Processes European Contract Partners: LABORELEC, Linkebeek, (B) SCK-CEN, CEN, Mol (B), Coordinators AEA Harwell, (UK) DPRSN/ITN, (P) CEA, Cadarache, (F) Loughborough University, Chemical Eng.Dpt (UK)

15 LLW Feeds and Membrane Processes Evaluated LLW UMM Electrochemical ion-exchange (EIX), Reverse Osmosis (RO), Nanofiltration (NF) LLW Harwell Electrochemical ion-exchange (EIX) LLW PWR Electrochemical ion-exchange (EIX), Electrodialysis, Volatilisation

16 Main Objectives of the Portuguese Participation Evaluate the potentiality of the EIX and RO/NF for: Removal of radium and other heavy metals from U milling wastes. Compare their potential with the conventional process of precipitation.

17 Aim of the Portuguese research Obtain good water recovery back to the milling process Minimize pollutants in the discharges Reduce chemicals used in the effluents treatment facility Reduce the final volume of the solid phases (sludges)

18 Tasks Simulated wastes (lab-scale) Genuine wastes (lab and pilot-scale) Tests performed in Portugal and UK Changes in the process gave fluctuations in the wastes received for treatment

19 Experimental Units tested Commercial bench-top RO unit: polyamide membranes (0.3 m 3 area); pre-filtration Commercial pilot-plant plant unit RO/NF unit: designed for sea water desalination; flat and spiral wound membranes (NF)

20 RO/NF Bench-top Experiments Bench-top unit designed by Millipore for basic feasibility studies (Laborelec) Membranes 5µm Cuno cartridge filter 1 µm Cuno betapure cartridge filter Polyamide membrane, area 0.3 m 2

RO LAB Simulant Feed (mg/l) Permeate (mg/l) Rejection (%) Genuine solution Rejection Feed Permeate (mg/l) (mg/l) (%) SO 2-4 2320 8 99.7 3400 6.9 99.8 Fe 2+ 80 0.5 99.4 670 36 94.6 Fe t Ca 2+ 160 0.

23 RO LAB Simulant Feed (mg/l) Permeate (mg/l) Rejection (%) Genuine solution Rejection Feed Permeate (mg/l) (mg/l) (%) SO Fe Fe t Ca Cl Mg Mn , Na U Ra (mbq/l)

24 Feed X main components Typical conc. (mg/l) SO Cl Fe 2+ 3 Fe 50 RO membranes rejection values % NF membranes % Ca > 95 > 80 Mg Mn Na Uranium 4 Radium 770 mbq/l Lab-scale Real solutions Lab-scale Real solutions

28 RO/NF Pilot-plant in-situ experiments Membranes Flat membranes using a Rochem Unit designed for sea water desalination Spiral wound membranes from Kiryat Weizmann for NF (larger pore size) Good for ph 0-14

29 Pre-Treatments for In-Situ Experiments To increase ph To reduce TDS and improve turbidity values by adding polyelectrolytes To avoid membrane scalling from calcium sulphate pp by adding Dequest 2051 phosphonate Also: feed aeration to oxidize the ferrous ions to ferric ions, subsequent pp of all ferric hydroxides followed by silica sand filtration (best for practical and economic reasons)

30 All in All in-situ RO experiments had to be carried out with protected membranes Pre Pre-filtration on sand filter and cartridge filter Use of an auxiliary tank between effluent entry and sand filter for solution aeration and to absorb occasional ph and concentration peaks: VRF of 3.2, water recovery 70%

34 Findings just a few Very good DF (90-100) VRF still far from being excellent (3.2 and 70% water recovery) Entrapment of colloidal iron and sulphates on membrane surface! High conc of calcium in the genuine feed streams is a problem! Pre Pre-treatments with polyelectrolytes proved efficient to reduce total dissolved solids Aeration to oxide ferrous ions to ferric ions, pp of ferric hydroxides and sand filtration proved to be the best pragmatic solution! Both RO and NF have good potential to remove contaminants from acidic wastes BUT need further improvement!

35 A few words about the remediation activities being carried out Being carried out by a Company setup the Portuguese Government (EDM) In close contact with IAEA recommendations and EU legislation (visits to Vienna and discussions with technical advisers) Monitored by DPRSN/ITN, and Portuguese Environmental Agency Periodic visits from the Article 35 Euratom inspectors to the sites being remediated. Positive reports were delivered All data recorded and available for inspection All lab analysis (gamma and alpha) made in certified labs in Spain or at ITN. Private companies make only surface gamma spectroscopy of soils with equipment calibrated at ITN

36 New and Old problems Mine water resulting from underground mines being flooded Question: How to treat mine water avoiding the use of the traditional process that increases sludges?

39 New Project?! Combined technologies The future? 1 st st Biorremediation: Desulfovibrio desulfuricans/vulgaris reduce highly soluble hexavelant uranium to tetravalent uranium(pp as uraninite); Pseudomonas Acidophilic Fe-oxidizing bacteria good for U accumulation Would these be also good for radium? 2 nd nd Phytorremediation: Myriophyllum spicatum (uptake of contaminants at root level) and Lemna minor, Riccia fluitans (uptake by all plant) 3 rd rd Membrane processes: for the polishing of the outlet of the previous treatments

Treatment of tailings water for re-use in an antimony mine

Treatment of tailings water for re-use in an antimony mine Desalination and Water Treatment www.deswater.com 34 (2011) 330 335 October 1944-3994/1944-3986 2011 Desalination Publications. All rights reserved doi: 10/5004/dwt.2011.2887 Treatment of tailings water