Is it commercially possible to extract uranium from groundwater (content varying from 100 to 1000 ppb) by using nano filter membrane?
I doubt that filtering removes uranyl ions from a solution, except you associate it with colloids. The best way to remove would be using a resin like LEWATIT, which is a well proven method in German drinking water processing plants.
Dear Ajoy,
Radionuclides removal using membrane technology
Information about radionuclides removal by membrane technology (high pressure RO–nanofiltration (NF) membranes) is very limited. It is usually mentioned in the literature that RO/NF membranes remove at least 95% of radionuclides, in addition to improving other water quality parameters that may be a concern. Salts are concentrated in brine and the overall efficiency of their removal is over 99%.
In [36] three different RO modules (thin-film polyamide hollow-fibre, low-pressure composite spiralwound, and thin-film composite) were tested. For the standard pressure modules (the first and the third module) 226Ra rejection exceeded 99%, whereas for the low-pressure module it was 91%. In all three cases, radium rejection slightly exceeded hardness rejection, suggesting that hardness monitoring might be used as a surrogate for radium. According to Havener, RO systems have demonstrated an ability to remove 87–98% of the radium present in drinking water. Similar elimination can be achieved for alpha particle activity and total beta and photon emitter activity. A disadvantage of the membrane technology is generation of 15–25% of highly concentrated (by a factor of four, if the RO system design value is 75% of recovery) radioactive wastewater (retentate) flow, which
as a low-level radioactive waste will have to be disposed of in accordance with local regulations. Other factors to consider in RO-based radium removal systems are the possible need for pretreatment and the possibility of high capital and operating costs. However, continuing advances in membrane technology
are bringing RO for radionuclides removal into a more competitive position.
Radionuclides removal using ion exchange processes
Of the numerous alternatives for radium removal (cation exchange softening, lime softening, RO, hyperfiltration, electrodialysis, sorption onto HMO, and sorption onto
barium sulphate-impregnated resins and alumina) sodium cation exchange softening has received the most attention for application to small and medium-sized
water systems because of its relative simplicity and economy. In this process, contaminated water is passed through a bed of strong acid cation (SAC) resin
in the sodium form, which, when exhausted, is regenerated with 1–2 N NaCl or KCl. The exchange reaction is:
2R[Na] + Ra2+ = R2Ra + 2Na.
Clifford and Zhang concluded that adding a small amount (~10%) of a strong base anion (SBA) resin to the SAC resin (~90%) in a conventional water softener provides good radium and uranium removal during cyclic operation with sodium chloride or potassium chloride regeneration. At exhaustion, which occurs at hardness or radium breakthrough depending on how the process is operated,
most of the exchange sites are occupied by calcium or magnesium because these are the predominant cations and also competitors to radium in feedwater. Ion
exchange softening has two significant disadvantages: it adds sodium to the product water in exchange for calcium, magnesium, and radium, and it produces a
regenerant wastewater typically having about 100 times the radioactivity level of the raw water. The first disadvantage can be overcome by regeneration with KCl rather than NaCl. Potassium chloride has proved to be a much better regenerant for radium than sodium. As to uranium, conventional alum and iron coagulation,
lime softening, RO, and anion exchange have proved effective for its removal from drinking water and are considered the best available technologies (BATs)
by the US EPA for drinking water treatment. During pilot scale tests it was found that the SBA resin exhibited an enormous capacity for the uranyl carbonate complexes (UO2(CO3)2 2– and UO2(CO3)3 4–) prevailing in water in the pH range from 5.5 to 10. The exchange reaction with a chloride-form anion resin (R[Cl]) is:
4R[Cl] + UO2(CO3)3 4– = R4UO2(CO3)3 + 4Cl–
Elution of adsorbed uranium is easily accomplished with 3–5 bed volumes of 1 N sodium chloride (NaCl), sodium nitrate (NaNO3), or ammonium carbonate
[(NH4)2CO3]:
R4UO2(CO3)3 + 4NaCl = 4R[Cl] + UO2(CO3)3 4– + 4Na+
For more information, please use the following link which contains a review article on the removal of radioactive materials entitled "Technology for the removal of radionuclides from natural water and waste management: state of the art " published by Rein Munter in Proceedings of the Estonian Academy of Sciences,
2013, 62, 2, 122–132:
http://www.kirj.ee/public/proceedings_pdf/2013/issue_2/Proc-2013-2-122-132.pdf
For commercially available RO and other nano-membranes, please use the following links:
http://www.lenntech.com/products/membrane/romembranes.htm?gclid=Cj0KEQjwrZ24BRC098fr-OqnuMkBEiQAKQ9lgLj0OvnJQsxVAntSerOfHeZdO-P5yqxvqpvPSo6CUpkaArz68P8HAQ
http://www.sciencedirect.com/science/article/pii/S0011916406001901
http://www.tandfonline.com/doi/abs/10.1080/01496390701560082
Hoping this will be helpful,
Rafik
Thanks Rafik Sir for Valuable information and also thanks to Mr,Ajoy for this question
Dr Ewald Schnug, Thank you very much for your response.
After you mentioned about Lewatit, I went through related articles, out of which one article says Lewatit® DW 630 can bring down the U concentration safely below 10ppb.
Does the efficiency vary when the samples range from 100ppb to 5000ppb? Can it bring down the U concentration to 10ppb when sample contains 5000ppb? What is the maximum range so far have been tested using Lewatit?
Regards
Dr Rafik Karaman,
Thank you so much for providing with the various possible methods with much details. The links provided by you were also of great interest for me.
Sir, besides applying these methods for separating radionucliides to improvise upon quality of water, can any of this technique be used to economic extraction of uranium if initial U-content in samples is about 1ppm?
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