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The solubilities of rare earth iodates
2414
Notes
I. inorg, nucLChem., 1966,Vol. 28, pp. 2414to 2416. PergamonPress Ltd. Printedin NorthernIreland
The solubilities of rare earth iodates (Received 28 January 1966; in revisedform 14 March 1966) EXCEPT for a few scattered values, ¢~-~)the solubilities of the rare earth iodates were not available in the literature. This information(s) was essential in the study of the coprecipitation behaviour of the rare earth iodates precipitated from homogeneous solution. (~) EXPERIMENTAL The rare earth iodates were prepared by dissolving about 10 g of rare earth oxide (99.8 and 99.9 ~o purity) in about 200 ml of water and an excess of nitric acid. A solution containing a slight stoichiometric excess of recrystallized reagent grade potassium iodate was slowly poured, with stirring, into the nitric acid solution of rare earth. The precipitated rare earth iodates were separated and then agitated with 15 ml of water at 80°C for several hours to remove any soluble species, such as rare earth nitrate, potassium iodate, etc. that were retained as impurities. The supernatant liquid was discarded. This washing process was repeated twenty times. Four different procedures were used to reach equilibrium between the purified rare earth iodates and water. Procedure L A 1-ml graduated pipette was packed with about 1-2 g of rare earth iodate and then placed in a constant temperature cabinet at 25.0 4- 0.2°C. About 1 ml of water was passed through the packed pipette every 12 hr. The resulting solution was collected and analysed. Several solutions were passed through the packed pipette a second time with no increase in dissolved rare earth iodate. Procedure II. About 10 g of rare earth iodate and 15 ml of water were placed in a 50-ml Erlenmeyer flask, which was fitted with an air-cooled condenser, and placed on an oscillating hot plate at 80°C for 8 hr. The flask was allowed to cool to 25°C with agitation for 24 hr and then placed in a constant temperature cabinet at 25.0 4- 0-2°C for several days. Procedure IIL About 10 g of rare earth iodate and 15 ml of water were placed in a 50-ml Erlenmeyer flask and agitated on an oscillating hot plate at 25.0 + 0.3°C for 48 hr. Procedure IV. About 10 g of rare earth iodate and 25 ml of water were placed in a 50-ml flask and agitated at 25.0 4- 0.3°C for 48 hr. The contents were then transferred to a 100-ml beaker and agitated at 25.0 4- 0-3°C for 24 hr to allow some water to evaporate. The rare earth iodate solutions obtained from all four procedures were centrifuged to remove any suspended particles. A check for suspended particles was made by passing a beam of polarized light through the solutions. These clear solutions were then analysed. RESULTS The iodate was determined by an iodometri¢ titration using a standard thiosulphate solution and starch as an indicator. The iodate concentration of the equilibrium solutions obtained by each of the four procedures is shown in Table 1. These values are known with an uncertainty of 2 per cent or less. As Table 1 indicates, the solubility values of the rare earth iodates obtained by procedures I, II and IV agree very well. The solubility values obtained by procedure HI have not quite reached equilibrium. (t) E. RIMBACHand A. SCHUS~T, Z. phys. Chem. 67) 188 (1909). (2) W. D. HARICINSand W. T. PEARCE,J. Am. chem. Soc. 38, 2694 (1916). (s) V. K. LAMER and F. H. GOLDMAN,J. Am. chem. Soc. Sl, 2632 (1929). (') ft. N. I~ARC~ and W. C. OELKE,J. phys. Chem. 42, 95 (1938). (5) M. E. PRUITr, R. R. RICKARDand E. I. WYATt, Anulyt. Chem. 34, 283 (1962). (s) F. H. FmSCHINOand T. R. PAUL, paper presented at First Midwest Regional Meeting, American Chemical Society, Kansas City, Mo., November, 1965. (T) F. H. FIRSCmNO, paper presented at First Midwest Regional Meeting, American Chemical Society, Kansas City, Mo., Novemt~r, 1965.
Notes
2415
TABLE I.--=DETERMINATIONOF IODATE CONCENTRATION* Procedures
Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Y
I
II
III
IV
3"1 3"4 3"1 2"6 2'4 2"7 2'8 3'1 3"5 4"1 4"4 4"9 5.8
3"1 3'4 3"1 2-6 2"4 2"7 2-8 3"1 3"5 4.1 4"4 4"9 5.8
3'0 3'3 3"0 2"5 2"3 2.6 2'7 3"0 3"4 3.9 4"3 4"8 5-6
3"1 3'4 3"1 2"6 2'4 2.7 2'8 3'1 3'5 4.1 4'4 4.9 5.8
* (moles/l) (10a). The tri-valent cations, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm and Yb, were analysed by the method of SrZWAZO and KATOts~ using a Cary-14 recording spectrophotometer. The spectra of the equilibrium rare-earth iodate solutions were compared to spectra of known solutions of pure rareearth perehlorates. The equilibrium solutions were also scanned in the u.v., visible and near-infra-red regions and the resulting spectra were compared to known rare-earth spectra. In this manner the equilibrium solutions were checked for rare earth impurities. The colourless cations, La and Y, were determined by an E D T A titration with methylthymol and xylenol orange indicators. Thus the concentration of both the rare earth cation and iodate anion were determined. For a formal stoichiometric relationship, the ratio of cation to anion would be 1 : 3. Experimental results are very close to this ratio. This data, given in Table 2, was obtained using procedure II. TABLE 2.--DETERMINATIONOF RARE EARTH A N D IODATE CONCENTRATIONS*
La Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Y
Cation
Anion
1.00 4- 0.02 1.10 4- 0.02 0-98 4- 0.02 0.81 ± 0.05 0"80 i 0"06 0.91 4- 0"05 0"90 4- 0"01 1.00 -4- 0"06 1"15 q- 0'03 1"40 4- 0"04 1"45 4- 0"06 1"65 4- 0-07 1.90 4- 0"02
3.1 3.4 3.1 2-6 2"4 2.7 2"8 3'1 3'5 4"1 4"4 4"9 5.8
* (moles/l) (108). ~a~ D. C. STEWARDand D. KATO, Analyt. Chem. 30, 164 (1958).
2416
Notes DISCUSSION
Two fundamentally different approaches were used to reach equilibrium. One approach (procedures II and IV) was supersaturation and subsequent discharge to equilibrium. The other approach (procedures I and HI) was the slow attainment of equilibrium. As a further check on the procedures of reaching equilibrium, the solubilities of zinc iodate and cadmium iodate were also determined. These solubilities checked very closely with values obtained by other workers: 3,x°~ TABLE 3.--Ac'rivrrY PRODUCTS Ionic
(gap) (1013) strength* La Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Y
12 17 12 6.4 4-8 7.4 7.7 12 20 39 44 61 110
6.2 6.6 6.2 5.2 4.8 5.4 5.6 6.2 7.0 8.4 8.8 9.8 11
* (moles/l) (103). From the solubility data given in Table 2, the activity products, given in Table 3, were calculated. Activity coefficients were calculated using the ionic strengths of the equilibrium solutions and ion size data of KarmLAND.~n~ An ion size value of 4 was used for iodate, and 9 for all the rare earths. Despite the fact that a value of 9 was given for only trivalent lanthanum, cerium, praseodymium, neodymium, samarium and yttrium it could still be used for all the rare earths. A 10 per cent change in the ion size value did not produce any significant change (less than 2 per cent) in the calculated activity products for the other rare earths. Even though some eomplexing of the rare earth cation with iodate probably occurs, it was assumed that such interaction did not significantly alter the free anion and cation concentrations. The solubilities of the rare earth iodates and the rare earth bromates(12~showed the same trends.
Acknowledgement--The support of this work by the United States Army Research Office-Durham through Grant No. DA-ARO(D)-31-124-GS17 is gratefully acknowledged. Science and Technology Division Southern Illinois University Edwardsville, Illinois 62025
F. H. FmSCmNG THOMAS R. PAUL
~9~W. C. OELKEand C. WAGNER,Proc. Iowa Acad. Sci. 41, 187 (1939). ~1o~j. E. RICCI and G, J. N~SSE,J. Am. chem. Soc. 64, 2305 (1942). ~11~j. I~LLAND, J. Am. chem. Soc. 59, 1675 (1937). ¢12~H. Sa~PrmNs and T. STEPrmNS, Solubilities of Inorganic and Organic Compounds, Macmillan, London (1963).
Notes
I. inorg, nucLChem., 1966,Vol. 28, pp. 2414to 2416. PergamonPress Ltd. Printedin NorthernIreland
The solubilities of rare earth iodates (Received 28 January 1966; in revisedform 14 March 1966) EXCEPT for a few scattered values, ¢~-~)the solubilities of the rare earth iodates were not available in the literature. This information(s) was essential in the study of the coprecipitation behaviour of the rare earth iodates precipitated from homogeneous solution. (~) EXPERIMENTAL The rare earth iodates were prepared by dissolving about 10 g of rare earth oxide (99.8 and 99.9 ~o purity) in about 200 ml of water and an excess of nitric acid. A solution containing a slight stoichiometric excess of recrystallized reagent grade potassium iodate was slowly poured, with stirring, into the nitric acid solution of rare earth. The precipitated rare earth iodates were separated and then agitated with 15 ml of water at 80°C for several hours to remove any soluble species, such as rare earth nitrate, potassium iodate, etc. that were retained as impurities. The supernatant liquid was discarded. This washing process was repeated twenty times. Four different procedures were used to reach equilibrium between the purified rare earth iodates and water. Procedure L A 1-ml graduated pipette was packed with about 1-2 g of rare earth iodate and then placed in a constant temperature cabinet at 25.0 4- 0.2°C. About 1 ml of water was passed through the packed pipette every 12 hr. The resulting solution was collected and analysed. Several solutions were passed through the packed pipette a second time with no increase in dissolved rare earth iodate. Procedure II. About 10 g of rare earth iodate and 15 ml of water were placed in a 50-ml Erlenmeyer flask, which was fitted with an air-cooled condenser, and placed on an oscillating hot plate at 80°C for 8 hr. The flask was allowed to cool to 25°C with agitation for 24 hr and then placed in a constant temperature cabinet at 25.0 4- 0-2°C for several days. Procedure IIL About 10 g of rare earth iodate and 15 ml of water were placed in a 50-ml Erlenmeyer flask and agitated on an oscillating hot plate at 25.0 + 0.3°C for 48 hr. Procedure IV. About 10 g of rare earth iodate and 25 ml of water were placed in a 50-ml flask and agitated at 25.0 4- 0.3°C for 48 hr. The contents were then transferred to a 100-ml beaker and agitated at 25.0 4- 0-3°C for 24 hr to allow some water to evaporate. The rare earth iodate solutions obtained from all four procedures were centrifuged to remove any suspended particles. A check for suspended particles was made by passing a beam of polarized light through the solutions. These clear solutions were then analysed. RESULTS The iodate was determined by an iodometri¢ titration using a standard thiosulphate solution and starch as an indicator. The iodate concentration of the equilibrium solutions obtained by each of the four procedures is shown in Table 1. These values are known with an uncertainty of 2 per cent or less. As Table 1 indicates, the solubility values of the rare earth iodates obtained by procedures I, II and IV agree very well. The solubility values obtained by procedure HI have not quite reached equilibrium. (t) E. RIMBACHand A. SCHUS~T, Z. phys. Chem. 67) 188 (1909). (2) W. D. HARICINSand W. T. PEARCE,J. Am. chem. Soc. 38, 2694 (1916). (s) V. K. LAMER and F. H. GOLDMAN,J. Am. chem. Soc. Sl, 2632 (1929). (') ft. N. I~ARC~ and W. C. OELKE,J. phys. Chem. 42, 95 (1938). (5) M. E. PRUITr, R. R. RICKARDand E. I. WYATt, Anulyt. Chem. 34, 283 (1962). (s) F. H. FmSCHINOand T. R. PAUL, paper presented at First Midwest Regional Meeting, American Chemical Society, Kansas City, Mo., November, 1965. (T) F. H. FIRSCmNO, paper presented at First Midwest Regional Meeting, American Chemical Society, Kansas City, Mo., Novemt~r, 1965.
Notes
2415
TABLE I.--=DETERMINATIONOF IODATE CONCENTRATION* Procedures
Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Y
I
II
III
IV
3"1 3"4 3"1 2"6 2'4 2"7 2'8 3'1 3"5 4"1 4"4 4"9 5.8
3"1 3'4 3"1 2-6 2"4 2"7 2-8 3"1 3"5 4.1 4"4 4"9 5.8
3'0 3'3 3"0 2"5 2"3 2.6 2'7 3"0 3"4 3.9 4"3 4"8 5-6
3"1 3'4 3"1 2"6 2'4 2.7 2'8 3'1 3'5 4.1 4'4 4.9 5.8
* (moles/l) (10a). The tri-valent cations, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm and Yb, were analysed by the method of SrZWAZO and KATOts~ using a Cary-14 recording spectrophotometer. The spectra of the equilibrium rare-earth iodate solutions were compared to spectra of known solutions of pure rareearth perehlorates. The equilibrium solutions were also scanned in the u.v., visible and near-infra-red regions and the resulting spectra were compared to known rare-earth spectra. In this manner the equilibrium solutions were checked for rare earth impurities. The colourless cations, La and Y, were determined by an E D T A titration with methylthymol and xylenol orange indicators. Thus the concentration of both the rare earth cation and iodate anion were determined. For a formal stoichiometric relationship, the ratio of cation to anion would be 1 : 3. Experimental results are very close to this ratio. This data, given in Table 2, was obtained using procedure II. TABLE 2.--DETERMINATIONOF RARE EARTH A N D IODATE CONCENTRATIONS*
La Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Y
Cation
Anion
1.00 4- 0.02 1.10 4- 0.02 0-98 4- 0.02 0.81 ± 0.05 0"80 i 0"06 0.91 4- 0"05 0"90 4- 0"01 1.00 -4- 0"06 1"15 q- 0'03 1"40 4- 0"04 1"45 4- 0"06 1"65 4- 0-07 1.90 4- 0"02
3.1 3.4 3.1 2-6 2"4 2.7 2"8 3'1 3'5 4"1 4"4 4"9 5.8
* (moles/l) (108). ~a~ D. C. STEWARDand D. KATO, Analyt. Chem. 30, 164 (1958).
2416
Notes DISCUSSION
Two fundamentally different approaches were used to reach equilibrium. One approach (procedures II and IV) was supersaturation and subsequent discharge to equilibrium. The other approach (procedures I and HI) was the slow attainment of equilibrium. As a further check on the procedures of reaching equilibrium, the solubilities of zinc iodate and cadmium iodate were also determined. These solubilities checked very closely with values obtained by other workers: 3,x°~ TABLE 3.--Ac'rivrrY PRODUCTS Ionic
(gap) (1013) strength* La Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Y
12 17 12 6.4 4-8 7.4 7.7 12 20 39 44 61 110
6.2 6.6 6.2 5.2 4.8 5.4 5.6 6.2 7.0 8.4 8.8 9.8 11
* (moles/l) (103). From the solubility data given in Table 2, the activity products, given in Table 3, were calculated. Activity coefficients were calculated using the ionic strengths of the equilibrium solutions and ion size data of KarmLAND.~n~ An ion size value of 4 was used for iodate, and 9 for all the rare earths. Despite the fact that a value of 9 was given for only trivalent lanthanum, cerium, praseodymium, neodymium, samarium and yttrium it could still be used for all the rare earths. A 10 per cent change in the ion size value did not produce any significant change (less than 2 per cent) in the calculated activity products for the other rare earths. Even though some eomplexing of the rare earth cation with iodate probably occurs, it was assumed that such interaction did not significantly alter the free anion and cation concentrations. The solubilities of the rare earth iodates and the rare earth bromates(12~showed the same trends.
Acknowledgement--The support of this work by the United States Army Research Office-Durham through Grant No. DA-ARO(D)-31-124-GS17 is gratefully acknowledged. Science and Technology Division Southern Illinois University Edwardsville, Illinois 62025
F. H. FmSCmNG THOMAS R. PAUL
~9~W. C. OELKEand C. WAGNER,Proc. Iowa Acad. Sci. 41, 187 (1939). ~1o~j. E. RICCI and G, J. N~SSE,J. Am. chem. Soc. 64, 2305 (1942). ~11~j. I~LLAND, J. Am. chem. Soc. 59, 1675 (1937). ¢12~H. Sa~PrmNs and T. STEPrmNS, Solubilities of Inorganic and Organic Compounds, Macmillan, London (1963).