Elution technology

There are many research investigations and reports about stripping uranium from uranyl sulphate solution-saturated resin. The most commonly used stripping agents are chloride, nitrate, dilute sulphuric acid (or addition sulphate) and carbonate. When chloride and nitrate is used to strip uranium from loaded resin, the resin is converted to Cl^– or NO3– type. After the elution, resin is transferred back to the adsorption phase and in the next adsorption, the Cl^– or NO3 will be passed back into barren solution. When discharged, the ions can cause environment pollution. If the barren solution is directed back to the leach section, a lot of Cl^– and NO3– ions will accumulate in the leached liquor. This sort of leach liquor will greatly reduce the resin loading capacity in the adsorption process. When sulphuric acid and sulphate is used as the elution agent to strip uranium from loaded resin, the adsorbed solution can be recycled totally to the leach process. The intense fractional process can be used in this elution system to improve the stripping efficiency. The intense fraction process is carried out in a fixed-bed column. In this process, the loaded resin is contacted with eluents containing

different uranium contents, from higher to lower in the last elution process, and additional new eluent is added when necessary. With this technology, a very high pregnant solution concentration is achieved compared with the conventional stripping process. This is very effective in treatment of the lower loading uranium resin obtained by ion exchange recovery of uranium from uranium effluent and mining water. The elution agent was 1 mol/l H2SO4 + 1.5 mol/l (NH4)2SO4. The elution contact time was 24 minute. The results are shown in Figure 8 and Table 7.

0 1 2 3 4 5 6 7

0 500 1000 1500 2000 2500 3000

V/Vc Uranium concentration in outlet effluent, mg/l

FIG. 7. Bench test adsorption curve for D263B resin.

0 2000 4000 6000 8000 10000 12000

0 2 4 6 8 10 12 14

V/Vc Uranium concentration in stripped solution, mg/l

Conventional stripping result Fractional stripping result FIG. 8. Intense fractional process stripping results.

Table VII. Intense fractional process stripping results with conventional stripping results

It can be seen from Figure 8 and Table 6 that by using the intense fractional process, the elution peak uranium concentration is much higher than that of the conventional elution process and the pregnant liquor volume is half that of the conventional elution process. When elution termination uranium concentration is about 5-mg/l uranium, the elution bed volume is about equal in both process. This result indicates that the intense fractional process is very effective.

In these experiments eight time recycling was carried out. The system reached equilibrium in the fourth recycle. The later five-recycle experimental results are shown in Table 8.

Table VIII. Results of the intense fractional process, effluent acidity 2.10 N Stripping peak liquor Eluted Resin

Recycle

It is indicated by Table 8 that the average pregnant liquor uranium concentration was 9.19 g/l when stripping peak liquor bed volume was 1.0. Average total elution bed volume was 12.4 which is about equal the conventional stripping process. The elution efficiency was 99.27%.

In the end, the compositions of elution liquor in 8th recycle time of different bed volume are shown in Table 9.

It can be seen from Tables 8 and 9 that acidity is lower in the stripping peak liquor. After the peak liquor bed volume, the acidity is basically stable in 3~13 bed volume. This is beneficial for maintaining high intense fractional process efficiency as well as for recovering uranium in the later precipitation process. The sulphate ion has some accumulation in the process that did not influence the stripping efficiency.

Table IX. The compositions of elution liquor in 8^th recycle

In general, the intense fractional process can be employed to strip uranium from the lower loading uranium resin, which achieves higher pregnant elution liquor. The pregnant liquor is reduced to one bed volume, and uranium concentration is increased two times. Over 50% of the eluent agent is saved compared with the conventional stripping process. This is also beneficial in the following neutralization process in uranium precipitation. So, when ion exchange resin is used to purify uranium effluent, the intense fractional process is a better and very effective way to recovery uranium.

4. Conclusions

From the study on the adsorption and elution property of four kind resins, the following points can be made:

— Acidity of adsorption solution has a great influence on resin adsorption of uranium.

TS-25 resin, D263 resin, D263B resin and 201×7 resin can be used in a wide pH range from 1.8 to 10.But hydroxyoxime resin can only be used in weak alkali or alkaline solution. The higher the pH value, the better the adsorption.

— In acidic medium when adsorption reaches equilibrium, the uranium total distribution coefficient of TS-25, D263, 201×7 and hydroxyoxime resin is 6.33×10³, 2.78×10³, 1.42×10³, and 2.1×10² respectively. The resin adsorption capacity sequence is TS-25 resin > D263B resin > 201×7 resin.

— Adsorption dynamics experiments show that TS-25 resin and D263 resin have good adsorption properties. Adsorption rate is very fast (macropore> medium pore> Gel-type).

The adsorption mechanism in the beginning is controlled by particle diffusion and later becomes film diffusion limited.

— Breakthrough point volume of TS-25 resin and D263B resin are 2000~2500, and 250~500 bed volume number (liquid effluent volume/resin bed volume) respectively when uranium is between 11.2 mg/l and 5.4 mg/l and the contact time between 5 and 2 minute. The saturation bed volume number of TS-25 resin and D263B resin is 4000~7600 and 1100~2700, respectively. But the D263B resin shows a better improvement in operating properties for dilute uranium solutions.

— Of the four kind of resins tested, D263B resin shows the best elution property under the experiment conditions. The intense fractional process is very effective for stripping uranium from the lower loading uranium resin. The pregnant liquor is reduced to one bed volume, and the uranium concentration is increased two times. Over 50% of the eluent agent is saved compared with the conventional stripping process.

So, in general, macropore resin TS-25 and medium pore resin D263B show better adsorption properties compared with 201×7 resin. In practice, the mining water normally contains about 2 mg/l uranium and process water contains about 5 mg/l uranium. TS-25 and D263B resin can be used to adsorb uranium for purifying these effluents. In decommissioned uranium mines and mills areas, D263B resin is a good choice because it not only shows better adsorption property, but also shows the best stripping property. With the intense fractional process, D263B can effectively recovery uranium from very dilute uranium effluent.

ACKNOWLEDGEMENTS

The authors wish to thank the Messrs. Dang Shungin, Tou Jianguo, and He Wanglin for provision the resin samples. Thanks are also due to Mr. Xu Jiazhong and other people involved in this project.

REFERENCES

[1] PAZ COSMEN RUIZ, M.L., Use of a fluidized bed ion exchange system for heavy metals removal from waste streams. International Symposium on Hydrometallurgy 1994.

Institution of Mining and Metallurgy & the Society of Chemical Industry, Chapman &

Hall, (1974) p. 741.

[2] SLATER, M.J., Continuous ion exchange plant design methods and problems.

Hydrometallurgy 4, (1979) p. 299–316.

[3] Environment protection article (II), Environmental Office, Metallurgy industry, (1977).

[4] ZHANG YONG, XU GEFU, Ion exchange and extraction of uranium, nuclear energy publisher, (1991) p. 156.

[5] GODDARD, J.E., The intense fraction process. In C.C. Gold II, Ion exchange for pollution control. Boca Raton. Fla., Chemical Rubber Co. (1979) p. 123–128.

Barium chloride precipitation-sludge recycle to treat acidic uranium