Solvent Extraction of Cerium (III) and Yttrium (III) by Carbonic Acids from Nitrate Medium

T. Litvinova St. Petersburg State Mining Institute, St. Petersburg, 21 line, Russia Die Daten in Extraktion von Zerium (III) und Ytter (III) durch Ölsäure- und Naphtensäurelösungen in Oxylol aus Nitratmedium sind erhalten. Mit Abhängigkeiten des Verteilungskoeffizienten von pH und des Bestandes der organischen und wässrigen Phase sind Festdaten und Gibbsenergien der Extrakti- onsgleichgewichten ausgerechnet, der Bestand der Solvatationskomplexe ist bestimmt. Experimental data were obtained on solvent extraction of cerium (III) and yttrium (III) from nitrate media with solutions of oleinic and naphthenic acids in o-dimethylbenzene. Composition of solvate complexes as well as constants and Gibbs energies of the extraction equilibrium were calculated bas- ing on dependences of the distribution coefficient on pH and composition of the organic and aqueous phases.

1 Introduction 2 Experimental Study It is possible to use such sources of technogenic In the experimental part of the investigation we pollution as tailings storages, refuse ores, waste studied solvent extraction of Ce (III) and Y (III) water from mining-and-metallurgical plants as from binary water solutions, which contained sources of high-value raw materials i.e. non- 0.01 mol/kg of these elements, with 0.5 M solu- ferrous and rare-earth metals. It can be feasible tion of oleinic or naphthenic acids in o- to recover valuable components from leaching dimethylbenzene as the extractant. As the result solutions or waste water by solvent extraction of these experiments we obtained the dependence method. Use of tributyl phosphate (TBP) in this of Ce and Y distribution coefficients on pH level case is uneconomical because of its high cost and and extractant concentration in the organic toxicity level. phase. The aim of this research was to study ce- Fig. 1 shows dependence of the distribution coef- rium (III) and yttrium (III) behavior in solvent ficient D on pH levels at constant value of the extraction with carbonic acids from nitrate me- extractant concentration. dium. Ce (III) and Y (III) distribution coefficients are increasing with increasing pH levels. In case of naphthenic acid yttrium (III) is extracted better than cerium. On application of oleinic acid at pH

Fig. 1: Dependence of Ce and Y distribution Fig. 2: Dependence of Ce and Y distribution coefficients on pH levels. coefficients on extractant concentration levels. Vorbeugemaßnahmen zum Schutz von Grundwasser und oberirdischer Gewässer 195 57. Berg- und Hüttenmännischer Tag Behandlungstechnologien für bergbaubeeinflusste Wässer

4−5, yttrium (III) is not extracted into organic rium constant and distribution coefficient is de- phase, which creates conditions for extraction scribed with the following equation: separation of rare earth metals of cerium and ⎛⎞a + =+−−++H yttrium groups. lg D lg Kγ ± zpH (3 z) lg⎜⎟ 1 ⎝⎠K d (Eq. 2) Dependence of the distribution coefficient on (3−−− z) lg(C (3 z)C ) extractant concentration was investigated at con- extr org ± stant pH values of 5.0 0.1 and molecular ratio of Dependences of distribution coefficient lgD on carboxylic acids to metal, which was equal to 4. pH-function: Results of this experiment are presented in ϕ(pH)zpH(3z)lg[C=+− −−− (3z)C] Fig. 2. extr org

⎛⎞a + , (Eq. 3) Distribution coefficient is increasing with the (3−+ z) lg 1 H increase in extractant concentration. The depend- ⎜⎟ ⎝⎠K d ence is almost equal, some difference being apparent when the extractant concentration is no which shown on Fig. 3, and the extractant con- less than 0,3 mol/l. As opposed to cerium (III), centration function the value of yttrium (III) distribution coefficient ϕ(С ) = lg[C − (3 − z)C ], (Eq. 4) practically does not depend on oleinic acid con- extr extr org centration. This also enables solvent extraction which shown on Fig. 4, were built based on ex- separation of cerium (III) and yttrium (III) in perimental data to calculate the solvate number oleinic acid in a wide range of extractant concen- (3-z) and Gibbs energies of the extraction proc- trations. ess calculated for different z values. Results of individual experiments show that salt Analysis of dependences 3a and 4a show that anions do not enter extraction solvate. So the yttrium (III) solvate number in extraction with extraction process can be described with the naphthenic acid equals 3 and the extraction proc- following reaction: ess can be described with the following equilib- 3+ + + − − rium: Me(aq) zH2O (3 z)R(org) ' + + + 3 + + + Y(aq) 3HR (org) ' YR3(org) 3H(aq) (Eq. 5) Me(OH)z R3− z(org) zH(aq) (Eq. 1) where the correlation between extraction equilib- Analyzing dependences 3b and 4b we calculated the value of cerium (III) solvate number as 2.33.

2,50 2,00 a b 2,00 1,502 1 1,50 3 3 1 1,00 1,002 lgD(Ce) lgD(Y) 0,50 0,50

0,00 0,00 -10,00 -5,00 0,00 5,00 10,00 15,00 -0,50 -10,00 -5,00 0,00 5,00 10,00 15,00 ηpη ηpη 2,50 3,00

c 2,00 d 2,50 3 2 1,50 2 2,00 3 1 1,00 1 1,50 lgD(Y) 0,50 lgD(Ce) 1,00

0,00 0,50 -10,00 -5,00 0,00 5,00 10,00 15,00 -0,50 0,00 -15,00 -10,00 -5,00 0,00 5,00 10,00 15,00 -1,00 -0,50 η pη ηpη Fig. 3: Dependence of Y(III) (a, c) and Ce (III) (b, d) distribution coefficient log on рН function in extraction with 0.05 М naphthenic acid (a, b) oleinic acid (с, d) at z=0 (1), z=1 (2), z=2 (3).

Vorbeugemaßnahmen zum Schutz von Grundwasser und oberirdischer Gewässer 196 T. Litvinova Solvent Extraction of Cerium (III) and Yttrium (III) by Carbonic Acids…

+ This indicates simultaneous progressing of the YOH R +1,65H (Eq. 11) following reactions: 1,65 1,35(org) (aq) 3+ + - It is seen from analysis of dependences 3a and 4a Сe(aq) 3R (org) ' CeR3(org) (Eq. 6) what an extraction of cerium (III) by oleinic acid is carried out with the solvate number of yttrium and is equal 2 and extraction process can be describes 2+ + - by follow equilibrium: СeOH(aq) 2R (org) ' CeOHR 2(org) , (Eq. 7) Ce3+−++ H O 2R ' CeOHR+ H+ (Eq. 12) which sum with factors of proportionality, corre- (aq) 2 (org) 2(org) (aq) sponding to one or another form of cerium (III) Table 1 shows comparison characteristics of content, gives up the following chemical equa- solvent extraction of cerium (III) nitrates and tion of cerium extraction with naphthenic acid: yttrium (III) nitrates with solutions of the follow- + − Ce3 + 0,67H O + 2,33R ' ing compounds in o-dimethylbenzene: tributyl (aq) 2 (org) phosphate (20%), trialkylbensylammonium ni- + + CeOH0,67R 2,33(org) 0,67H(aq) (Eq. 8) trate (0.5 M), naphthenic acid (0.5 M) and oleinic acid (0.5 M). The analysis of the dependences 3c and 4c show, what extraction of yttrium (III) by oleinic acid is As it is apparent from Table 1, reduction of sol- carried out with value of yttrium (III) solvate vate number and conversion from ion-exchange number 1,35 and it point on salvation process of extraction to solvate extraction leads to a de- hydroxyl complexes of yttrium (III): crease in the distribution coefficient. 2+ + - In extraction with naphthenic acid, the values of YOH(aq) 2R (org) ' YOHR 2(org) (Eq. 9) solvate number and distribution coefficient of yttrium (III) are more than those of cerium (III). and This is explained by a great ionic potential (z/r + Y(OH) + R - ' Y(OH) R (Eq. 10) ratio) of yttrium i.e. lesser crystallographic radius 2(aq) (org) 2 (org) of this element as compared to cerium. Thus, Summary, extraction process is described by yttrium (III) forms stronger bonds with acid ani- follow equation: ons that displace water from the first coordination sphere. Oleinic acid is weaker than 3+ + + − Y(aq) 1,65H2O 1,35R(org) ' naphthenic acid. At pH 5 the naphthenic acid is

2 c 2 a

1,5 1, 5 1 2 1 3 1 1

lgD(Y) 2 l gD( Ce)

0,5 0, 5

0 0 0,00 1,00 2,00 3,00 4,00 0,5 0,6 0,7 0,8 0,9 1 1,1 1,2 (CНNaft) (CHNaft) c 1,2c 2,5 1 2

0,8 1,5 2 1 0,6 1 lgD(Y) 1 lgD(Ce) 0,4 2 3 3 0,2 0,5

0 0 01 23401 23 45 )CHOl (CHOl)

Fig. 4: Dependence of Y(III) (a, c) and Ce (III) (b, d) distribution coefficient log on extractant concentration function in extraction with 0.05 М naphthenic acid (a, b) oleinic acid (с, d) at z=0 (1), z=1 (2), z=2 (3).

Vorbeugemaßnahmen zum Schutz von Grundwasser und oberirdischer Gewässer 197 57. Berg- und Hüttenmännischer Tag Behandlungstechnologien für bergbaubeeinflusste Wässer

Tab. 1: Characteristics of solvent extraction of cerium (III) nitrates and yttrium (III) nitrates with solutions of various extractants.

– Δ G 0 , Solvate num- Extractant Element рН D r 298 kJ/mol ber yttrium 5 7.5±0.3 4.1±0.2 2 Tributyl phosphate cerium 5 9.0±0.4 6.3±0.3 1.6 Trialkylbensylam- yttrium 3 10.2±0.4 7.9±0.5 1 monium nitrate cerium 3 35±4 8.9±0.3 1 Naphthenic acid yttrium 5 78.5 27.6±0.4 3 pKd = 5,1 cerium 5 39±1 36.2±0.3 2.33 Oleinic acid yttrium 5 10.1±0.2 33.1±0.4 1.35 pKd =5.9 cerium 5 100±3 58.6±0.7 2 halfway dissociated whereas oleinic acid practi- tion durch Karbonsäuren mit dem Scheidungs- cally does not dissociate under such pH condi- faktor 10 für Ölsäure und 2 für Naphtensäuren tions. Thus, hydrogen cations should be dis- gezeigt. Extraktion der EsE durch Naphtensäure placed from non-dissociated molecule of oleinic ist durch überwiegenden Übergang der Kationen acid during the extraction process: Me3+ und teilweise der Hydroxokomplexe [МеОН]2+ in die organische Phase bedingt. Die (3− z) +− ' [Me(H2m O) (OH) z(aq) ] (3 z)HR (org) Extraktion der EsE durch Ölsäure verläuft durch +− + Solvatation der Kationen Me3+ und teilweise der [Me(H O)−− (OH) R − ] (3 z)H (13) 2 m (3 z) z (3 z) (org) (aq) Hydroxokomplexe [МеОН]2+. Thereat, water molecules that are less tightly Die Bedeutung der Gibbsenergie des Extrakti- bound with metal cations are displaced during 3+ onsprozesses von Zerium und Ytter durch Naph- the extraction process. On the one hand, Y ten- und Ölsäure ist erhalten. Die Senkung der cations are more hydrated than Ce3+ cations and + Solvatationszahl und Übergang von der Extrakti- less readily displaces H in the extractant mole- on durch Lonenaustauschmechanismus zur Sol- cules. On the other hand, yttrium (III) is more 2+ vatation führt zur Steigerung der Gibbsenergie hydrolysable than cerium (III) (ΔfG([YOH] ) = 2+ des Extraktionsprozesses und folglich zur Sen- −28.86 kJ/mol, ΔfG([СеOH] ) = −25.87 kJ/mol), kung des Verteilungskoeffizienten. so yttrium (III) has lesser charge of extractive hydrocomplex, less readily interacts with oleat- ion and is characterized with a lower solvate 4 Conclusion number. It is possible to separate the rare earth metals of In case of naphthenic acid, naphthenic ions read- cerium and yttrium groups by method of solvent ily displace water from the first coordination extraction with carbonic acids with separation sphere. Besides, yttrium Me—Naft bond strength factor 10 for oleinic acid and 2 for naphthenic is stronger because of small ion radius, which acid. results in higher value of yttrium distribution Extraction of rare earth metals by naphthenic coefficient as compared to that of cerium. acid is due to conversion of Ме3+ and, partially hydroxyl complexes [МеОН]2+, into organic − +I 3+ +I − If we study the OH ⎯⎯→⎯1 Me ←⎯⎯⎯2 R phase. system, then the I2 inductive effect is higher than that of I due to π-bond of the carboxyl group Extraction of rare earth metals with oleinic acid 1 takes place due to salvation of cations [МеOH]2+ with the bond order of 1/2, which easily polar- + izes increasing the inductive effect. This facili- and, partially, hydroxyl complexes [Ме(ОН)2] tates displacement of OH− and results in higher into the organic phase. index of yttrium solvate number then in the case Data of Gibbs energies of the extraction equilib- with oleinic acid, yttrium being characterized by rium were obtained for extraction of cerium (III) higher level of polarizing action than cerium. and yttrium (III) by naphthenic and oleinic acids. Reduction of solvate number and conversion 3 Zusammenfassung from ion-exchange extraction to solvate extrac- In dem Artikel wird die Möglichkeit der Extrak- tion leads to an increase of Gibbs energies of the tionsscheidung der Elemente der seltenen Erden extraction process and, as a consequence, to de- der Zerium- und Yttergruppen durch die Extrak- crease in the distribution coefficient.

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