Magnetic cesium adsorbent, preparation method therefor, and cesium removal method using same

1. A method of preparing a magnetic metal hexacyanoferrate for use as a cesium adsorbent, said method consisting of:

subjecting a metal hexacyanoferrate having a cubic crystal structure to a hydrothermal reaction at a temperature in the range of from about 120° C. to about 200° C. to convert the cubic crystal structure of said metal hexacyanoferrate to a rhombohedral crystal structure; and

optionally isolating and drying said metal hexacyanoferrate having the rhombohedral crystal structure.

2. The method according to claim 1 , wherein, in the metal hexacyanoferrate having the cubic crystal structure, the carbon atoms of the cyano ligands form six coordinate bonds with the ferric ion, and the nitrogen atoms of the cyano ligands form six coordinate bonds with a metal ion.

3. The method according to claim 2 , wherein the metal ion is a nickel or manganese ion.

4. The method according to claim 3 , wherein, when the metal ion is a nickel ion, the metal hexacyanoferrate having a rhombohedral crystal structure shows XRD peaks at 17, 24, 25, 35, 38.5, 39.8, 49.5, 51, 53.5, 56.2 and 57.4 2θ (±0.2°).

5. The method according to claim 3 , wherein, when the metal ion is a manganese ion, the metal hexacyanoferrate having a rhombohedral crystal structure shows XRD peaks at 17, 23.5, 24.2, 34.2, 37.8, 38.5, 48.2, 49.5, 52.2, 54.8 and 55.6 2θ (±0.2°).

6. The method according to claim 3 , wherein an average particle size of the metal hexacyanoferrate having a rhombohedral crystal structure is 0.1 μm to 1 mm.

7. The method according to claim 3 , wherein the metal hexacyanoferrates having a rhombohedral crystal structure agglomerate together to form a cluster.

8. The method according to claim 1 , wherein the hydrothermal reaction is performed at 120 to 200° C. under a pressure of 2 to 15 bar for 20 minutes to 20 hours.

9. The method according to claim 8 , further comprising the steps of isolating and drying said metal hexacyanoferrate having rhombohedral crystal structure.

10. The method of claim 8 , wherein said magnetic metal hexacyanoferrate comprises nickel hexacyanoferrate or manganese hexacyanoferrate.

11. A method of removing cesium, comprising:

adsorbing cesium by dispersing a magnetic cesium adsorbent in a solution containing a cesium ion to produce a cesium-adsorbed magnetic cesium adsorbent; and

separating said cesium-adsorbed magnetic cesium adsorbent using a magnet or filter.

12. The method according to claim 11 , wherein a cesium adsorption rate represented by Mathematical Expression 1 below is 90% or more:

Cesium adsorption rate (%)=(concentration of cesium in solution before separation−concentration of cesium in solution after separation)/concentration of cesium in solution before separation×100.  [Mathematical Expression 1]

13. A method of preparing a magnetic metal hexacyanoferrate having a rhombohedral crystal structure, said method consisting of:

(a) placing a metal hexacyanoferrate having a cubic crystal structure in water to produce a mixture;

(b) heating the mixture to a temperature in the range of from 120° C. to about 200° C. at from about 2 to about 15 bar of pressure to convert the cubic crystal structure of said metal hexacyanoferrate to Rail the rhombohedral crystal structure; and

(c) optionally isolating and drying said magnetic metal hexacyanoferrate having the rhombohedral crystal structure.

14. The method of claim 13 , wherein said step (b) of converting cubic crystal structure of said metal hexacyanoferrate to a rhombohedral crystal structure comprises subjecting the aqueous solution to said temperature and pressure conditions for a time ranging from about 20 minutes to about 20 hours.

15. The method of claim 13 further comprising the steps of isolating and drying said magnetic metal hexacyanoferrate having a rhombohedral crystal structure.

16. The method of claim 13 , wherein an average particle size of said magnetic metal hexacyanoferrate having a rhombohedral crystal structure ranges from about 0.1 μm to about 1 mm.

17. A method of removing cesium from a sample comprising cesium, said method comprising:

(a) contacting a solution comprising said sample with a magnetic cesium adsorbent to produce a cesium-adsorbed magnetic cesium adsorbent complex, wherein said magnetic cesium adsorbent comprises a metal hexacyanoferrate having a rhombohedral crystal structure; and

(c) removing said cesium-adsorbed magnetic cesium adsorbent complex from said solution using a magnet or a filter.