9.4.3 Fundamental Parameters. Concentration Factor. Not recommended. See Extraction factor. Decontamination Factor

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1 9.4.3 Fudametal Parameters Cocetratio Factor Not recommeded. See Extractio factor. Decotamiatio Factor The ratio of the proportio of cotamiat to product before treatmet to the proportio after treatmet. It is the reciprocal of the erichmet factor. Distributio Coefficiet This term is ot recommeded as a syoym for distributio ratio. Distributio Costat A syoym for partitio ratio. Distributio Ratio (i liquid-liquid distributio) (D) The ratio of the total aalytical cocetratio of a solute i the extract (regardless of its chemical form) to its total aalytical cocetratio i the other phase. If there is possible cofusio with the extractio factor or (mass) distributio ratio, the term cocetratio distributio ratio (symbol D C ) should be used, but this is ot commo usage. This is reasoably compatible with chromatographic omeclature. (iv) The terms distributio coefficiet, extractio coefficiet ad, where appropriate, scrubbig coefficiet, strippig coefficiet are widely used alteratives but are ot recommeded. If they must be used i a give situatio the term ratio is preferable to coefficiet. I equatios relatig to aqueous/orgaic systems the orgaic phase cocetratio is, by covetio, the umerator ad the aqueous phase cocetratio the deomiator. I the case of strippig ratio the opposite covetio is sometimes used but should the be clearly specified. I the past there has bee much cofusio betwee the distributio ratio as defied above, the value of which varies with experimetal coditios, e.g. ph, presece of complexig agets, extet of achievemet of equilibrium etc. ad the true partitio costat which is by defiitio ivariable or the partitio coefficiet or distributio costat which apply to a particular chemical species uder specified coditios. For this reaso the terms distributio costat, partitio

2 costat, partitio coefficiet, partitio ratio ad extractio costat should ot be used i this cotext. (v) (vi) The use of the ratio: light phase cocetratio to heavy phase cocetratio is ambiguous ad is ot recommeded. The distributio ratio is a experimetal parameter ad its value does ot ecessarily imply that distributio equilibrium betwee the phases has bee achieved. Erichmet Factor (i liquid-liquid distributio) (S) The factor by which the ratio of the amouts of two substaces i the feed must be multiplied to give their ratio after treatmet. Q A /Q B = S A,B (Q' A /Q' B ) where Q A ad Q' A are the fial ad iitial amouts of species A ad Q B ad Q' B are the fial ad iitial amouts of species B. Hece S A,B = E A /E B where E is the fractio extracted. I terms of D,, r (where is the umber of stages ad r the phase ratio. S A, B = 1 1 (1 + (1 + rda ) rd ) B Extractability A property which qualitatively idicates the degree to which a substace is extracted. Note: This term is imprecise ad geerally used i a qualitative sese. It is ot a syoym for fractio extracted. Extractio Coefficiet This term is ot recommeded as a syoym for distributio ratio. Extractio (Equilibrium) Costat at Zero Ioic Stregth (K o ex) The equilibrium costat of the distributio reactio expressed i terms of the reactig species. Thus, for the gross reactio: M + aq + HL org ML, org + H + aq i which the reaget HL iitially dissolved i a orgaic phase reacts with a metal io M + i aqueous solutio to form a product ML which is more soluble i the orgaic phase tha i water,

3 o aml a, org K = ex a a + M, aq + H, aq HL, org Whe cocetratios are used istead of activities or mixed terms are employed as whe H + ad/or M + are measured with a electrode, the appropriate ame is extractio costat, symbol K ex, accompaied by a careful defiitio. K o ex may be termed the thermodyamic extractio costat. The extractio costat is related to other terms relevat to such systems by: K ex = D β ML DHL K a where β is the overall formatio costat of ML ad K a is the dissociatio costat of HL. Whe the reaget HL is more soluble i water tha the other immiscible phase it may be more coveiet to defie a special equilibrium costat i terms of HL aq : Kex = DML β K a (iv) I distributio equilibria ivolvig o-aqueous systems, e.g. liquid SO 2, molte salts ad metals, the mass actio equilibrium costat for the relevat extractio process ca be idetified with K ex which should be explicitly defied i this cotext. I actual practice, it may be ecessary to iclude other terms to take ito accout other complexes formed by auxiliary reagets ad the solvatio ad/or polymerizatio of the various species. I such cases, K ex must be defied with referece to the relevat explicit chemical equatio. A example is complex formatio betwee the metal io ad a ucharged crow ether or cryptad molecule followed by io-pair extractio: M + aq + L org + A - aq (ML +. A - ) org K ex = [M [ML + aq + A [L - org org[a aq (v) Use of Rigbom's "coditioal extractio costat",

4 K eff ex = a + H [ M ' [ ML' aq org [ HL' org i cojuctio with alpha coefficiets is useful. See PAC (1994). (vi) (vii) The phases ca also be specified by the formula of the solvet or by other symbols (preferably Roma umerals) or by overliig formulae referrig to oe phase, usually the less polar oe. The subscript aq (or w) is ofte omitted; aq is preferable to w as the latter is appropriate oly i Eglish ad Germa. The qualificatio "Equilibrium" is ofte omitted. (viii) The terms partitio costat ad distributio costat must ot be used i this sese. Extractio Factor (D m ) The ratio of the total mass of a solute i the extract to that i the other phase. It is the product of the (cocetratio) distributio ratio ad the appropriate phase ratio. It is syoymous with the cocetratio factor or mass distributio ratio, this latter term beig particularly apt. The term cocetratio factor is ofte employed for the overall extractio factor i a process or process step. Fractio Extracted (E) The fractio of the total quatity of a substace extracted (usually by the solvet) uder specified coditios, i.e. E A = Q A /Q' A where Q A is the mass of A extracted ad Q' A is the total mass of A preset at the start. E may be expressed as a percetage, %E. The term extractability is qualitative ad should ot be used as a syoym for fractio extracted. If the aqueous phase is extracted with successive portios of solvet, the phase volume ratio (solvet/feed) beig r each time, the fractio extracted is give by:

5 E = 1 - (rd + 1) - If = r = 1, E 1 = D/(1 + D) this expressio is a cocept of value i chromatography theory. (iv) The fractio extracted is also kow as the recovery factor, especially for a multistage process. Loadig Capacity The maximum cocetratio of solute(s) that a solvet ca cotai uder specified coditios. The terms maximum loadig, saturatio capacity ad saturatio loadig are syoymous. All the above terms should clearly be distiguished from ultimate capacity. Mass Distributio Ratio See Extractio factor. Maximum Loadig See Loadig capacity. Partitio Coefficiet This term is ot recommeded ad should ot be used as a syoym for partitio costat, partitio ratio or distributio ratio. Partitio Costat (K D o ) The ratio of activity of a give species A i the extract to its activity i the other phase with which it is i equilibrium, thus (K D o ) A = a A,org / a A,aq Its value should ot vary with compositio but depeds o the choice of stadard states ad o the temperature (ad evetually the pressure). Note: See Trasfer activity coefficiet.

6 Partitio Ratio (K D ) The ratio of the cocetratio of a substace i a sigle defiite form, A, i the extract to its cocetratio i the same form i the other phase at equilibrium, e.g. for a aqueous/orgaic system (K D ) A = [A org /[A aq K D is sometimes called the distributio costat; this is a good syoym. The terms distributio coefficiet, distributio ratio, partitio costat ad extractio costat should ot be used as syoyms for partitio ratio. The use of the iverse ratio (aqueous/orgaic) may be appropriate i certai cases, e.g. where the orgaic phase forms the feed but its use i such cases should be clearly specified. The ratio of the cocetratio i the deser phase to the less dese phase is ot recommeded as it ca be ambiguous. If the pure solvet ad ifiitely dilute feed are take as the stadard states, K D K D o as the total cocetratio of dissolved materials decreases. ph 0.5 or ph 1/2 That value of ph i a aqueous phase at which the distributio ratio is uity at equilibrium. Note: 50% of the solute is extracted (E = 0.5) oly whe the phase ratio is uity. Phase Ratio (i liquid-liquid distributio) (r) The ratio of the quatity of the solvet to that of the other phase. Uless otherwise specified the phase ratio refers to the phase volume ratio. If other aspects of the phase ratio are employed viz. phase mass ratio, phase flow ratio, these should be specified. Recovery Factor This term is ot recommeded. Fractio extracted should be used. Saturatio Capacity See Loadig capacity.

7 Saturatio Loadig See Loadig capacity. Selectivity Coefficiet This term should ot be used as a syoym for separatio factor. Note: This term has a specific meaig i relatio to io exchage by solid exchagers. See Selectivity Ratio Syoym for selectivity coefficiet. It should ot be used as a syoym for separatio factor. Separatio Coefficiet This term is ot recommeded. A syoym for separatio factor. Separatio Factor (i liquid-liquid distributio) (α A,B ) The ratio of the respective distributio ratios of two extractable solutes measured uder the same coditios. α A,B = D A /D B By covetio the solutes desigated as A ad B i the above are chose so as to make α>1. The term separatio coefficiet is ot recommeded. The terms selectivity coefficiet ad selectivity ratio are ot syoymous ad should ot be used. Stoichiometric Capacity See Ultimate capacity. Trasfer Activity Coefficiet (γ t ) A term used to quatify the differece i the free eergy of a solute io i two differet stadard states ofte i two differet liquid phases. The relatioship is t G o = ν R T lγ t

8 where t G o is the trasfer Gibbs eergy ad ν is the umber of ios i the solute. See partitio costat. See IUPAC Iformatio Bulleti No. 34 (1974) for full details. It should ot be cofused with the mass trasfer coefficiet which represets the specific rate of trasfer of a species from oe phase to aother. It does ot ecessarily imply the physical trasfer of a solute betwee two liquid phases. Ultimate Capacity The theoretical maximum capacity of a solvet cotaiig a give cocetratio of extractat for a solute uder ay coditios. Note: Where appropriate the term stoichiometric capacity ca be used.

Chapter 14: Chemical Equilibrium

Chapter 14: Chemical Equilibrium hapter 14: hemical Equilibrium 46 hapter 14: hemical Equilibrium Sectio 14.1: Itroductio to hemical Equilibrium hemical equilibrium is the state where the cocetratios of all reactats ad products remai