Indian Journal of ChemistryVo!' 23A, February 1984, pp. 140-142

Solvent Extraction of Mercurvd l) from Hydrochloric Acid Solution byHigh Molecular Weight Amine, Amberlite LA-I

ANIL K DE", UDAY S RAY & NARAHARI PARHlt

Department of Chemistry, Visva-Bharati, Santiniketan 731235

Received 28 April 1983: revised and accepted 4 Dejohn 1983

A selective method for the extraction of milligram amount of Hg(Il) from hydrochloric acid solution with liquid anionexchanger. Amberlite LA-I in chloroform has been proposed. The optimum concentration of hydrochlonc acid ISfoun~ to be0.05 M onwards. Quantitative extraction has been achieved with the diluents like benzene,. xylene. toluene, carbontetrachloride. nitrobenzene and chloroform. Extraction of mercury is found to be quanutauve with amine pretreated withHCI, even without external addition of HC!. The separation. of Hg(l I) from several syn}heUc m_Ixt~~es IS found. to. bequantitative. The probable composition of the extracted species IS found to be [( R2NH, ), (HgCl4) l The extractionbehaviour of the secondary amine, Amberlite LA-I has been compared With that of tertiary am me like trioctylamine.

In recent years solvent extraction with high molecularweight amines and quaternary ammonium compoundshas been extensively used as a promising technique forthe removal of toxic elements like Zn, Cd, Hg, As, Cu,Pb, Cr etc., from industrial effiuents and for therecovery with purification of fertile and fissionablematerials from irradiated fuel in atomic energy centres.

The amines, due to their unique anion exchangeability, extract anionic metal complexes from theaqueous phase. Some work on liquid cationexchangers 1 has been reported from this laboratory.We have reported earlier? the extraction of zinc (II) byl.quid anion exchanger. The present work reports onthe selectivity of Amberlite LA-l in chloroform for theextraction of Hg(II) from its chlorocornplex. No suchwork has yet been reported in the literature:' - ~.

The secondary amine and its salt with anionichlorocomplex of mercury are essentially insoluble in

aqueous solution but exhibit high solubility in organicsolvents.

c;hterials and MethodsThe liquid anion exchanger, Amberlite LA-l (Rohm

and Haas) was used as such. Chloroform (ICI, AR) wasused as the diluent. The amine was suitably dilutedwith chloroform and converted into its chloride form;JYequilibrating with hydrochloric acid for 5 m~n. Themolar concentration of the amine was determined asreported earlier".

A stock solution of mercury (8.2 mg/ml) wasprepared by dissolving accurately weighedHg(N03h. H20 (BOH, AR) in doubly deionised wat~rand the solution was standardized by complexometrictitration with EDTA (disodium salt) using Mg-EDTAand Eriochrome Black T indicators.

tUGC Teacher Fel\ow on leave from U.N. College, Soro. Orissa.

;40

All solyent extractions were carried out at 27"± 1.0cC.

General extraction procedureThe ratio of the volumes of aqueous phase and the

organic phase was maintained at I: 1. An aqueoussolution containing 8.2 mg/ml of mercury was takenand to this standard hydrochloric acid was added tomaintain the required acidity (0.05 M HC\). The totalvolume of the aqueous phase was made upto 10 ml andequilibrated with a solution of the amine in chloroform(lOml; 2.5~<) vjv) for 5 min. The two layers wereallowed to settle for 5 min, the organic phase separatedand to the aqueous phase was added ammonia buffer(PH 10) and Mg-EDTA. The amount of mercurypresent in the aqueous phase was then determined bycomplexometric titration. To the organic phase wasadded 1.M HN03 (l Oml) and the mixture shaken for 5min. The two phases were allowed to settle, the organicphase separated again and the aqueous phasecollected. The organic phase thus obtained was againshaken with 1A1H~O, (10 ml) for 5 min and themixture allowed to settle. The organic phase wasseparated carefully and the aqueous phase collected.The aqueous phase (acid extract) of two successivestrippings was mixed and treated WIth Mg-EDTA andammonia buffer (pH 10) and the amount of mercuryextracted determined as discussed earlier.

Results and DiscussionThe extraction behaviour of Hg(11) with (a) amine

pretreated WIth hydrochloric acid and (b) free aminewas studied using constant concentration of metal (4.1x 10 :' M) and the extractant (0.045 M). It is observedthat the amine pretreated with hydrochloric acidquantitatively extracts mercury without externaladdition of hydrochloric acid (FIg.. l ). However, with

DE et al.: SOLVENT EXTRACTION OF MERCURY(H)

100f--_--!:::===t==--- ...•

• Amine pretreated with Hel

ct Free Amine

0'01 0'02 0'05 0'04 005[HCl].t::1

Fig. I--Extraction of Hg(II) with Amberlite LA-I as a function of[HCI)

free amine extraction per cent increases with increasein hydrochloric acid concentration and the extractionis quantitative at hydrochloric acid concentration> 0.05 M (Fig. I). This observation clearly points thedifference in the extraction behaviour of free amineand amine pretreated with hydrochloric acid (i.e.R2NH and R1NHiCI-). The distribution ratio iscalculated from the extraction data using the relation:

D = ~, ( IOO~-x)where V and V' are the respective volumes of theaqueous phase and organic phase and x is thepercentage of mercury extracted."!".

The extraction of Hg(II) has also been carried outusing a tertiary amine, trioctylamine(Fluka AG) underidentical conditions. Trioctylamine showed improvedextraction at lower acid concentration in comparisonto Amberlite LA-I though at optimum acidconcentration, the extraction of metal is almost equalin the two cases (see Table I).

In order to evaluate the probable reactionmechanism of Hg(lI) with chloride ion, the extractionexperiments were carried out with free amine using

Table \---Extractiun of Mercurytl l) as a Function ofHydrochloric Acid Concentration with Free Amine in

Chloroform

lHCl1 Extraction (oJ of Hg:(II).If

Amberlnv LA-! Trioctylarnine

'.5 x I () 3

5 »: 1075 x 10 '1.1), !O

24.4

51.370.081 293.997.591> 59lU

27.758.677.9

85.695.597.598.598.5

':':.0 x :03.5 x 10SO x 101.0 x 10 I

------ -~-------.--.---------

2

c

~o

-1-:5~--'----:-Z~---~-1log [CI-]

Fig.2-Plot of log D against log [CI -) at constant [amine)

varying concentrations of hydrochloric acid atconstant ionic strength of 0.15 M, maintained byadding sodium sulphate. However,nearly sameextraction results are obtained with or withoutmaintaining constant ionic strength. Plot of log Dagainst log [Cl-] is linear (Fig.2) with slope = 2,indicating the formation of (HgCI4)2 - in the aqueousphase. At lower chloride concentration, the formationof (HgCI3) - is also expected. Therefore, the reactionmechanism in the aqueous phase is proposed to be:

Hg2 ++ 3 HCI~HgCl3 + 3 H +Hg2+ +4HCI~HgCl~ -+4H+

At constant concentration of mercury (4.1x 10-3 M) and hydrochloric acid (0.1 M), theextraction of Hg(I1) as a function of amineconcentration in chloroform was studied. Theextraction of Hg(II) is quantitative provided the amine:mercury molar ratio is ~ 2. Plot of log D against log[amine] is linear with slope =2. Hence the reactionmechanism of Hg(Il) is proposed to be:

2(R2NH;)o + (HgCI4);-~[(R2NHi)z{HgCI4)2 --]org

The Hg (Ill-amine ratio in the extracted species IS

1:2. This result is further supported when theexperiments are conducted using varying con-centrations of metal. The ratio of metal to amineconcentration in organic phase is again found to be 1:2,thereby corroborating the proposed stoichiometry ofthe extracted species.

Mercury was extracted with 2.5~~amine solution invarious diluents. The results indicate quantitativeextraction of mercury with benzene, xylene, toluene,carbon tetrachloride, nitrobenzene and chloroform.Further stripping of mercury from the organic phasewith 1M HN03 (IOml) is not complete in a singlestripping operation. Two successive strippings are

141

INDIAN J. CHEM., VOL 23A, FEBRUARY 1984

Table 2- Effect of Diverse on the Extraction of Hg(II) withAmberlite LA-I

[Hg(II), 8.25 rng; [HCI] =0.1 M]

Diverseions

Ca'+Sr2 +

Ba2+

Mg2+Mn2+

Ni21

Cr3+

Cu2+

Co2+

Fe"A13+

*Zn2 +

*Pb2+

SOiPOl

Amountadded(mg)

4004004003001007030404025

52020

1200500

Source

CaCI2·2H20SrCI,.6H20BaC12·2H20MgS04·7H20MnCI,.4H,ONiSO .•. 7H,OCr,(S04k6H20CuS04.5 H20CoS04·6H20FeCI3.6H,OAI(N03)3·9 H20Zn(AclzPb(N03lzNa,S04'1O H20KH,P04

'Extracted by R,NH;CI··· without adding HC!.

Mercuryextracted

(/0)

97.997.998.497.497.997.497.498.498.498.497.097.497.497.997.4

Table 3-Quantitative Separation of Hg(II) from SyntheticMixtures using Amberlite LA-l

[Hg(II) taken = 8.25 rng; [HCI] =0.1 M]

Mixture taken (mg)SampleNo.

Ca 2 t (200) + Sr ' +(200)2 Ca'+(2oo)+Ba'+(200)3 Sr ' + (200) + Ba 2+(200)4 Ni2+(35)+ Cu ' +(20)5 Cu2+(20) + C02+(20)6 Mn ' +(50) + Ni2+(30)7 Cr3 +(15) + Co2+(! 5)8 Fe3+(10)+Co'+(l5)9 *Zn2+(IO) + Ph2+(10)

10 Ca 2+(100) + Sr ' +(100) + Ba2+(IOO)II Mn ' +(30) + Ni2+(IO) + Cu2+(lO)12 Cr.1+(lOJ+Cu2+(lO)Co1+(lO)13 Fe3+(IO)+Cr3+(lO)+Co'+(lO)

*Extracted by R,NH;Cl without adding HC!.

142

Mercuryextracted

Co)

97.497.997.498.4

97.997.997.497.997.497.997.497.497.4

found necessary for quantitative stripping of mercuryfrom the organic phase. It is also observed that backextraction is complete with chloroform as the diluent.It appears that diluents also have some effect towardsback extraction. The optimum time of two successivestrippings for quantitative back extraction of mercurywith I M HN03 from the organic phase is found to be5 min for each stripping.

The effect of diverse ions on the quantitativeextraction of Hg(II) under optimum condition isshown in Table 2. The tolerance limit for such ions likecalcium, strontium, barium, magnesium, manganese,sulphate, phosphate are high and that of nickel,chromium, copper, cobalt, iron, aluminium are lowabove which extraction decreases. It is also found thatzinc and lead can be separated by pretreated amine(R2NH ;Cl-) without external addition of hy-drochloric acid.

Quantitative separation of mercury from some ofthe synthetic mixtures was attempted and the resultsare shown in Table 3. It has been possible to separatemercury from several ternary and quaternarymixtures.

AcknowledgementOne of the authors (NP) is grateful to the UGC, New

Delhi for award of teacher fellowship and also to thePrincipal, U.N. College, Soro, Orissa for study leave.

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1961,63.9 De A K, Khopkar S M & Chalmers R A, Solvent extraction of

metals (Van Nostrand, London) 1970,2.10 Morrison G H & Freiser H, Solient extraction in analytical

chemistry (Wiley. New York) 1957, 12.