Indian Journal of ChemistryVol. 25A. March 1986. pp.
)()().)01
Extraction ChromatographicSeparation of Gold Using
Bis(2-ethylhexyl)phosphoric Acidas an Extractant
LALIT C T EUSEBIUSt & S M KHOPKAR*
Department of Chemistry, Indian Institute of Technology,Powai,
Bombay 400076
Received 18 February 1985; revised 7 November 1985;accepted 20
January 1986
Bis(2-ethylhexyl)phosphoric acid (HDEHP), a liquid
cationexchanger coated on silica gel from benzene quantitatively
extractsgold from 7-8 M HCI and is stripped off with 2 M HCI. Gold
insynthetic mixtures containing other metal ions such as Cu(I1),
Ni(ll),Mn(I1), Pb(IV), Pt(IV) and Pd(I1) in the ratios actually
present invarious gold alloys has been successfully separated
employingHDEHP.
Bis(2-ethylhexyl)phosphoric acid (HDEHP), a liquidcation
exchanger is one of the common extractantsemployed for the
separation of metal ions such as rareearths, fission products and
transuranium metal ions!etc. Several methods are available/ -12 for
theextraction chromatographic separation of gold, butthe use of
HDEHP as the extractant for gold 13 -I b islacking. Presently we
have explored extractionchromatographic behaviour of gold using
HDEHP asan extractant in various concentrations of hy-drochloric
acid. The optimum conditions for itsextraction have been evaluated
and its separation from20 metal ions have been accomplished.
ECIL model GS 866C spectrophotometer providedwith matched corex
glass cuvetts of 10 mm optical pathlength was used for measuring
absorbance. ECILmodel 5651 pH-meter having glass-SCE
electrodeassembly was used for pH measurements. Thechromatographic
column (int diam =8 mm and length= 150 mm) was used for
chromatographic separation.
Stock solution of gold was prepared by dissolvingabout 0.45 g of
gold chloride (Johnson & Mathey) in0.1 M hydrochloric acid and
making the volume to 100ml with water. It was standardized
gravimetrically byhydroquinonel7 and was found to contain 400
Jlg/mlof gold. Dilute solution (40 Jlg/ml of gold) wasprepared by
appropriate dilution.
Bis(2-ethylhexyl)orthophosphoric acid (HDEHP)(Schuchardt,
Munchen, Germany) was used as such.
tPresent address: Department of Chemistry. Ewing
ChristianCollege. University of Allahabad. Allahabad 211003.
300
Purified silica gel (60-120 mesh. BDH) was renderedhydrophobic
by procedure described earlier I II. It wasthen coated with H D EH
P taken in benzene. The excessbenzene was removed by centrifugation
at 2500 rpmusing a Remi model T 8C centrifuge. This gel was usedfor
carrying out column extraction studies as well asfor reverse phase
extraction chromatographicseparation work.
General procedureA slurry of silica gel coated with HDEHP
was
transferred to a chromatographic column and theheight of the bed
was maintained at 8 cm. It waswashed with 2-8 M hydrochloric acid
(10-15 ml) as thecase may be. An aliquot of solution containing 40
Jiggold/ml was rendered acidic (8 M) by addinghydrochloric acid. It
was passed through thepretreated column at a flow rate of 1 ml/min.
Afterextraction, gold was stripped with 2 M hydrochloricacid.
Twenty fractions (each of 2 ml) were collected andgold from each
fraction was determined spectrophoto-metrically I 9 as the
gold-rhodamine complex inbenzene at 565 nm.
It was found that gold is quantitatively extractedfrom 7-8 M
hydrochloric acid. The gold thus extractedhad a breakthrough volume
above 60 ml and 90 ml at7 M and 8 M hydrochloric acid,
respectively.Therefore at 7-8 M hydrochloric acid, the
extractionbehaviour of other metal ions were studied. It wasnoted
that except iron and uranium all other metal ionswere not retained
by the column under the conditionsemployed for the extraction of
gold and they were allquantitatively recovered from within the
initialfractions (1-8) of 2 ml each. Gold which was retained inthe
column was finally stripped with 2 M hydrochloricacid. Thus from
7-8 M hydrochloric acid gold wasseparated from other metal ions
except iron anduranium.
It was observed that the optimum conditions forbatch extraction
of gold were not same as those forextraction chromatography 10.
This is the case withmany metal ions studied 11.1 II. The ions such
as copper(0.01 M), nickel (not extracted), manganese (PH 4.0),lead
(0.01 M), platinum and palladium (not extracted),silver (0.1 M),
cadmium (0.03 M) and antimony (0.1 M)were extracted at different
acidities of hydrochloricacid hence they passed through the column
in 7 Mhydrochloric acid medium facilitating separation ofgold from
binary mixtures.
It was possible to separate gold from binarymixtures containing
copper and gold or tellurium and
