analysis ofu ranyl carbonate complexes in an open...

Analysis of Uranyl Carbonate Complexes in an Open and Close System

ANALYSIS ofU RANYL CARBONATE COMPLEXES INan OPEN AND CWSE

ENVIRONMENTAL SYSTEM by ANALYTICAL CBlMISTRY

SABAT SIMBOWN*

ABSTRAKKOMPLEKS URANIL KARBONAT DI DALAM SISTEM LINGKUNGANTERBUKA DAN TEKTUTUP DITINJAU DARI SUDUT KIMIA ANALITIK.Diternngkan perubahaJl konsentmsi ion ~ 2- di dalam air alam pada lingkungan terbuka daD

terbltup berasal dari gas C~ yang te~ di udaIa teIbadap pH Jarutan. Reaksi antarn kationUO!+ dengan anion c~ 2- juga diternngkan dengan menggunakan perhitungan, peibandingan

antara masing-masing species kompleks manil kaIbonat terbadap niJai totalnya. Pernngkatlunak Lotus 123 release 2.4 digunakan untuk menghitung masing-masing molfiaksi darimasing-masing spesies kompleks manil kaIbonat terhadap pH lamtan. Didapatkan bahwaspesies kompleks urnnil kaIbonat di dalam air alam pada lingkungan terbuka pada kondisiasam lebih sederhana dibandingkan dengan di dalam air alam pada lingkungan tertutup.Sebaliknya kompleks manil kaIbonat di dalam air pada lingkungan telbuka daD daIamsuasana basa kandungannya lebih sederhana daripada di daIam air alam pada lingkunganterbltup.

ABSTRACTURANll- CARBONATE COMPLEXES IN OPEN AND CWSED ENVIRONMENTALSYSTEM FROM ANALYTICAL CHEMISTRY VIEWPOINT. Variation of C~ 2- ion

concentration from C~ gas originated from abDosphere, in nabJral water in an open andclose system versus pH of the solution is described. Reaction between u~ 2+ cation with

CO32-anion is also described by using calcuJation, comparison of each species of Ul3Dylcarbonate complexes to its total values. Each mol fiaction of uranyl corbonate complexversus pH of the solution is calculated using Lotus 123 release 2.4. It is found that Ul3Dylcarbonate complexes species in natural water which is slightly acid in an open system issimpler than that in a close syStem. On the other hand, uranil carbonate complexes species innaturnl water which is slightly base is simpler in an open system than that in a close system.

atmosphere because chemical andtransportation induStly are burning fossilfuel in large amount The huge amount ofC~ in abnosphere can be understood fromthe ~n house effect and corrosion of

INTRODUCTIONCarbon dioxide is an important element for

various processes, such as biological processof respirntion, biosynthesis and other.Recently C~ gas is rising rapidly in

.Researcher in the Re..c;earch and Development Center for Advanced Technology (p3TM)BAT AN

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1'31, log 132 and log 133 of U~CO3,UO2(CO3)22-., UOi~)34-. Theconcentrntion of uranyl ion or metal andcomplex ion in water is govemoo by pH ofthe solutiOll

This paper will discuss of uranylcarbonate and its complexes in an open andclose system in VaJying pH value by use ofLotus 123 as a tool for the calculationwhich is based on 131, !32and 133 values.

THEORYMost commonly used equilibrium

between carbonate species and hydrogen isHenry's constant, which is written asfollowsCO2 (gas) --:;. Caz (sol) k=~=lO-I.5Where khis Henry's constantCOz(gas) + H2O --:;. H2C~ Km=lO-2.8H2CO3 --:;. W+HC~- K1=lO-3.5H2CO3 --:;. W + HCO3- Kal=IO-6.3HCO3- _-:;.W+C~2- K.z= 10-1 0,3

steels which can become serious problems,especially in oil and petrochemical industries.

Compared with other gasses, C~ gas isquite soluble in water. Some of soluble CO2gas in water will react with water to formcarl>onic acid. Concentrn1ion of caIbondioxide in caIbonic acid solution depends onthe partial pressure of caIbon dioxide gas inatmosphere. A higller partial pressure ofcarl>on dioxide gas in atmosphere willproduce higher cocentration of CO2 insolution. So the chelnical equilibrium of thecarl>onate system pblYS an important role inenvironments, for it will react with othercation in naturnl water, such asCa2+, U~ 2+ ,&2+ ,Fe2+ etc.

Carbonic acid in water will dissociate intoits anions and cations, in two steps. Theamount of carl>onate ion in solution stronglydepends on the pH of the solution. H2COJ,HC~ + and C~ 2- are not found in solution of

the same pH. The amount of [C~r- insolution is not detennined only by pH of thesolution, but it is also detennined byproperties of the system. In an open system,the concentration of [CO3r- is higher thanthat in a close system, because CO2 gas isalways supplied by the atmosphere. On theother hand CO2 gas in a close system islimited.

Uranium, is an element wich has manyoxidation states (+3,+4,+5 and +6), in which+3 and +5 states are unstable, +4 is less stablein the air, and +6 stile is stable. Uranyl ion,UO22+ with oxidation state +6, is alwaysfound in uranium minerals, such as incarnotite -K2(u~h(VO4)2.3H2O,rutherfordine U~CO3 etc. RutherfordineU02C~ mineral is slightly soluble in water.

Sea and ground water always containurnnyl ion or uranyl carl>onate complex.These are caused by uranyl ion which has astrong tendency to form carl>onate complexesin caIbonate media, uranyl carl>onatecomplexes such as U02(C~h2-, UO2(CO3 h 4-

The relatively strong complexes of urnnylion with caIbonate can be seen ftom thevalues of log

Figure 1 shows the effect pH variation onmole fraction of each carbonate ions. It canbe seen that H2CO3 predominantly exists ina solution with pH less than 6. For pHUIKler 4, the amount of [HCO3]- and[~f- in solution are very low and theycan not be seen in mole fraction as seenfigure I above. [HC~)- existspredominantly in a range of 6 to 8,5. In thisrange, H2CO3 is decreasing drastically. In arange of 10 to 14, [CO3f- is predominant,while [HCO3]- is decreasing and H2CO3 isalmost nothing.

The amount of [CO3f- is necessary toknow because it will affect the results ofreaction of uranyl and carbonate ion. Forcalculating [C~f- concentl"dtion in openand close systems, the value of normalatmosphere is used. In normal atmosphere,the air contains 10-3,5 atm C~, while itsequilibrium with ~ (sol) can be obtainedfrom Henry's constant above, [H2C~] =[~ (sol)] =~ co2 = 10-1,5 X 10-5 M

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[C~]As mentioned above that the amount of[CO3f- in solution is not detennined only bypH of the solution, bllt also by properties ofthe system. Figure 2 shows that in an opensystem, carbonate species in solution arealways in equilibrium with C~ gas, so it isreasonable to take the concentration ofH2CO3 to be 10-5 M. For others species, suchas CO3 and HC03, they can be calculated asfollows.

= CTCO3 (l/(H)2/Kal Ka2+

(H)/Ka2+ 1» .(5)

From Figure 2, it can known as following.The amount of [CO3]2- in an open systemincreases linearly and rapidly for tile rangeof pH 1-11, while for pH > 11 it remainsconstant If tilere are some uranyl ion in anopened and close system, uranyl carbonatesand its complexes would be produced, foruranyl and carbonates ions will react toform uranyl carbonate first. Since uranylcarbonates will also react witil oiliercarbonate ion to form uranyl complexes, tileresult of tilose reactions are not simple. Asmentioned above, tile form and tileconcentration or mole fraction of carbonateion depend on tile pH of tile solution, tilereaction between uranyl and carbonate ionsdepends on pH of tile solution too. Forforming complex reaction between uranyland carbonates ions, it has to have enoughuranyl and carbonates ions in tile samesolution. The amount of each complex canbe calculated and it is based on tilechemical equilibrium of tile reaction below.Chemical reaction between uranyl andcarbonate ions can be written as follows.

(1)H2C~ ~HC~- +HI-

kal = (H1 [HC~]/ [H2C~]HCO3 ~ C~2- + H-

ka2 = (H1 [CO3]/ [H2C~] (2)

Since in an open system, the concentrntion ofH2CO3 is always constant at 10-5 M, then theconcentrntion of [HCO3J will be 10-5 X Kal /[H1 and log [HCO3J = -5 -pKal + pH = pH

-11,3. This equation produces a straight linefor [HCO3J versus pH as shown in figure 2.Similary, for [CO3J concentrntion which canbe calculated from eq 2 gives log [CO3J = -5 -pKal- PKaz + 2pH = 2pH -21,6. This

equation also produces a straight line for log[CO3J versus pH as shown in figure 2.

In a close system, carbonate system followsthe normal acid which dissociaties into 2species, HCO3- and CO32-respectively.

u~ 2+ + C~ 2- -+ U~CO3

~I = 1010 (6)

U~CO3 + CO32- -+UO2(C~)22-132 = 1017 (7)

U~(C~) 2 2- + C~ 2- -+ UO2(C~) 3 4-

133= 1021,6 (8)

H2C~ -+ HCO3 + ~tal = £H1 [HC~]! [H2CO3]

HCO3 -+ CO3 + Wka2 = £H1 [CO3]! [H2CO3]

If the total concentration of carbonates is 10-5M, the amount of (CO3r- , (HCOJJ- andH2CO3 then can be c.1.lcuJated. Based on thetnaSs balance, the total [CO3J is CTCO3 =(H2CO3J + (HCO3J + (CO3J = 10-5.

where 13 = Summed Fonnation ConstantK == Stepwise Formation Constant,

and131 = kl

132 = kl X k2

133 = kl X k2 X k3The lines for each of the C~ species can

be drawn by using the following expression.

.(3)

[H2CO3] = CTCO3 (1/(I+K..\/[H) +

2K..\ ~/[HI » [HC~] = CTCO3 (1/[H] / K..\ +

1+~/[H))

RESULT AND DISCUSSIONThe effect of pH on the H2Co3 amd itsions:Natural water containing carbonates andnuanyl ions will react to foOD uranyl.(4)

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H2C~ and the uranyl ion predomint in thesolution. In a solution of the pH less than 4,there is no reaction between H2Co3 anduranyl ion. Uranyl ion reacts with carl>onateion, if there is enough (c~f- in thesolution. In addition, if the (C~)2-concentration is very low, the concentrationof (U02)2+ will be governed by thesolubility of U02CO3. However, at higheJr(C~)2- concentration, reaction of eq (6,7,.&)above are driven to the right and the totaJIconcentration of dissolved (U~)2+ is;considerably greater than of (U~)2+ alone~then more complexes of uranyl carbonatewill be produced. The concentrntion ofuranyl decreases rapidly as pH increasesbecause there is reaction between uranyland carbonate ions to form simple uranylcarbonate and complex uranyl carbonate. IDla solution of pH>4 uranyl carbonat~ isformed, the maximum mole fractiom is;reached at pH closed to 7. Complex 1IJm(C~)2 2- is formed in the range pH 2: aDd

10, because the (C~ 2-) concentratj1i)D\ is;rising rapidly from 10 -125 to 10 -21.. 'DIeamount of U~C~ decreases for neutralcondition, exactly at pH>6,6 and at pH=9,the solution practically is run. Quit ofU02C~- On the other hand co~ ~(C03h 2- starts to form and it has, ~

to lnaximum mole fraction at pHi *.. 1Ikutmost complex of U~(CO3)3 4- s1DIIItr. liD

form at pH 6.5 and it has achieved tolnaximum at pH 10 as can be seen at FiIgJme3 below.

Uranyl ion has completely reacted! \t.iitilcarbonates at pH 7.4 as can! be SeJC1I1 iiIIFigure 3. In the range of pH 4 andi ]j(O) ~are 4 species of uranyL..caIiiQ1mta;,.meanwhile in the range of pH> ]]@) ~all uranyl and carbonates is in; dIe: :fiiImDl dUO2(CO3)3 4-. A solution coantiDg; ~and carbonate ions will produce- COmpb ~uranyl carbonate, its complex (t3JJl ]be:determined in simple uranyl! carbQDak'"simple uranyl carbonate compl~ 01f neaJIJ'uranyl carbonate complexes.

canbonate, through a simple reaction. Uranylcarbonate forms a complex with anothercarbonate ions, but through complexreactions, because the result is the sunbstancewhich is not simple and has a negativecharge. If carbonate ion is more than enoughin the solution containing uranyl carbonatecomplex, it will produce another uranylcarbonate complexes. That result is asubstance which has 3 ion carbonates and oneuranyl ion and has negative charge. As is seenin the eqs (6,7,8) the uranyl carbonate and itscomplexes strongly depend on the amount of(CO3)2- in open or close system.Based on the atmosphere normal conditionthe amount of species (HC~)- and (CO3)2- arefound from very low concentration ti highconcentration. The comparison between themcan be seen in figure 2, the same amount ofH2CO3 in close and opene system as a sourceof(C~)2- does not produce the same amountof (CO3)2- .Concentration of (C~)2- does notdependent on the pH ofvthe solution, but alsois dependent on the kind of the system.Concentration of (CO3)2- in close system ishigher than in opene system for pH 1 -6, butthe opposite is happ--'8ed for pH 7-14. FromFigure 2, it can be seen the (C~ 21 producedat pH = 8 in open system is about 10.(j and inclose system is about 10-7, meanwhile at pH =11, the (CO3 2-) in open system has aconcentration close to 1, while, the (C~)2- inclose system has a concentration 10-6. Thedifference in concentration of (CO3)2- whichis significantly high, will affect the result ofthe reaction between uranyl cation andcarbonates to from uranyl carbonate and itscomplexes, because the amount of uranylcomplex in natural water depends strongly onthe concentration of (C~)2-. Since theamount carbonate ion in natural waterdepends on the acidity or pH of the solution,so the result of the reaction between uranyland carbonates ion depends on the pH of thesolution.

In an open system, for example, at pH<4uranyl carbonates has not formed yet, becausethe concentration of C~ 2- is less than 10-10

as can be seen from Figure 2, carbonic acid

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Effect of colsed system for the form ofuranyl carbonate compleL

of UTilnYI caIt>Onate complexes UOz(C~h2 is fonned at pH = 4.6 until pH = 14 andUTilnYI caIt>Onate complexes UOz(C~)3 -4 is

fonned at pH 7.2 until pH = 14. UranylcaIt>Onate complexes UOz(C~h -2 become

maximum at pH = 10 and it decreases

slowly as pH increases, meanwhile uranylcaIbonate complexes UOz(C~)3 -4

increases slowly untul pH = 12, then

remains stable. In comparison, in opensystem at pH = 8 there are3 uranyl

caIt>Onate complexes, while in close systemthere are only two uranyl caIt>Onatecomplexes. In conttas, for pH more than 11,in open system there is only one uranylcaIt>Onate complexes as UOz(C~h -4,while in close system there are two uranylcaIt>Onates complexes. In neutral solutionopen system is more complicated than closesystem, but in base solution, close systembecomes more complicated than in opensystem. However, in acid solution, in opensystem is simpler than in closesystem.

Since the amount of carbonates in close andopen systems are different, it causes differentin the distribution of uranyl carbonatescomplex. Both the chemical reactioncalculations between uranyl and carbonateions in close and opensystem are the same butthe result are different,. because the amountof carbonate ions in open and close systemhas the same pH is different If the amount ofcarbonates ion in open and closed system arethe same, it will be produced the sameamount of uranyl carbonate complex. Sincethe calculation nethod and the 131, 132 and fuvalues are the same, so the result should besame.

All the calculations are based on the massbalance and total analytical concentrdtion.The mass balance eqution of UO2, in theUO2 containing substances is[U~]+[U~CO3 }t[U~( C~ h}t[U~( C~)3]= C total ofU~

CONCLUSIONS

2.

3.

Based on the composition of manylcaIbonates complexes, the source ofurnnyl complex can be predicted.The description of the above diagIamSare simple, since there are only twocomponents used. For actual open andclose environmental systems whichusually have more than twocomponents, such as CI-, NO3-, 804 2-

etc, the diagrams therefore will bemore complicated.If other cations in environmental is alsoconsidered as in forming uranylcarbonate complexes, they would haveproduced very complicated diagrams.In a slightly acid solution,in opensystem the composition of urnnyl andurnnyl caIbonate are nit mixed, but it ismixed in close system. In a slightlybase solution, on the contl3ry, thecomposition of urnnyl complexes aremore complicated in closed than inopened system due to concentration of[C~f

Each of the species of uranyl complex isthen compared to the total concentmtion ofuranyl complex. The result of that comparisonis called mole fraction of each species, that is[ U~ ] I C total of U~, mole fraction of[U~CO3] is [U~C~] IC total of U~ .Reaction between uranyl and caJt)onate withthe known equilibrimn above, for example,which is SliD of tile total concentrationuranyl, uranyl complex. It can be written as (1+ 1010 x [CO3] + 1017 x [CO3t + 1021,6 x[CO3f. Each mole fraction of the uranylcomplex can be seen itl Figure 4.

The disbibution of uranyl caJt)onatecomplex in Figure 4 is not similar to that inFigure 3 even the amount H2C~ is the same.That means the disbibution of uranylcarbonate complexes U~(C~)z -2 in both

systems are not the same. In addition, therange of formation of uranyl caJt)onatespecies is wider in Figure 4 than in Figure 3.Simple Uranyl CaIbonate has been formed atpH<2, meanwhile itl the opened syStemuranyl carbonate is formed at pH<4. Species

4.

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REFERENCES

1. ROJAS-HEMANDFZ, A et al~PREDOMINANCE-ZONE DIAGRAMIN SOLUTION CHEMISTRY. J.CHEMEDUC 1995 No 12 1099-1105

2. CHOPPIN, GREGPRY R; ASPECT OFNUCLEAR WASTE DISPOSAL OFUSE IN lEACHING NASICCHEMISTRY;J. CHEMEDUC 1994 No10 826-829

3.

4.

5.

NISmMURA. R et at; CORROSIONBEHA VIOUR AND HYDROGENCONTENT OF CARBON STELLS INC~ ENVIRONMENT; MA1ERIALSCIENCE RESEARCHINTERNATIONAL 1996, No 4 254-260.MACCA, C; UPTAKE AND WSS OFCARBON DIOXIDE IN VOLUMEI'RICANALYSIS J. CHEMEDUC 1986 No 8691-693SNOEYINK, V.L and JENKINS D;WATER CHEMISTRY. JOHN WILEY& SONS, NEWYORK 1980.

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pH

Fi.gure mole fraction of carbonate ions as a function of pH

Figure 3 : Distribution of complex urnnyl carbonates vs pH in opened system.

Figure 2. Logarithm of species HCO3- and CO32- versus pH in open and close system

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oo,,~-'00 2+I 2

~ 0.5 ~00.- (00\2 l ., 1."-

~~/'

09 1>11 1213 141 2'

, 3 4 5 6 7 8-Hpi

Figure 4 : Distribution of complex uranyl carbonates vs pH in close system

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Moh. Zen

analysis ofu ranyl carbonate complexes in an open...

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