Proposed Research Work
Solvent Extraction Separation of Platinum metals with N-n-hexylaniline
Introduction :
A platinum metals are rare elements of high economic value.
Chemically the platinum metals are less reactive than the most element, have luster
are softer or more ductile and have higher melting points than other metals. The group
of platinum metals ruthenium, rhodium, palladium, osmium, iridium, and platinum
they are better known for there uses in art, jewellery and coinage 1.
The platinum metals as platinum, palladium, rhodium, ruthenium, osmium have
some similar physical and chemical properties. These metals found in homogenously
and their concentrations in earth crust is very low. The concentrations of these metals
in rock materials is less than 10 ppb. Considering the above maintained aspects,
analytical chemist have challenge to sample preparations, extractions, separations and
their individual determinations. Due to high cost and wide applications it is essential to
have selective and sensitive, separations method for these metals.
Platinum metals are mostly found in South America, Columbia etc. platinum
occurs in the form of the mineral sperrylite (PtAs2) and remaining elements are occurs
along with platinum, nickel and copper mining industry. Platinum and palladium are
soft and silvery white while remaining metals are hard and brittle. These metals have
high melting and boiling points so they are used to make high temperature furnace, jet
engine fuel nozzles and laboratory crucible. Platinum is used to coat missile nose
cones. They are also used as catalyst in watches, surgical instrument, electrical
contacts, dental filling. Rhodium. Osmium are hard and brittle hence these are used for
hardening the alloy called as alloying agent2.
The literature study shows that limitations of separations and determinations of
individual metals from their ores and metallurgical concentrate. The whole analysis of
these precise metals are very complicated because they have similar properties and
found together, therefore it desirable to have versatile shame of analysis for extractions
and separations of all these platinum metals. Hence the extractions and separations of
these metals from their metallurgical concentrate using the solvent extraction
technique. Among the various methods solvent extractions method is very rapid,
versatile and popular technique because the extractions are carried out at micro and
macro levels. The solvent extraction technique has been carried out using the various
reagent have becomes popular. We are planning to use N-n-hexylaniline as a new
extractant which acts as a liquid anion exchanger for extractions of platinum metals.
The use of N-n-hexylaniline is used for solvent extractions of bismuth 3.
Literature survey:
The literature survey reveals that, the extraction of precious metals was carried
out by using various high molecular weight amines. The preparations of n-octylaniline
and its applications in extractions of noble metals have been describing earlier4.
Palladium(II) was extracted with N-n-octylaniline from hydrochloric acid medium 5.
Tellurium extracted with N-n-octylaniline in a halide media and its separations from
real samples 6. Solvent extractions and separations of rhodium(III) has been carried
out with N-n-octylaniline 7 in xylene in sodium malonate medium.
A novel method has been proposed for extractions of ruthenium(IV) from
hydrochloric acid medium with N-n-octylaniline and is applied for seprations of
ruthenium from the base metals 8. Lead(II) and bismuth(III) quantitatively separated
from each other with n-octylaniline in hydrochloric acid media 9. Gold(III) has been
extracted from aques halide media and sodium malonate
10-11
. Solvent extractions of
the osmium(VIII) has been carried out using the N-n-octylaniline and is separated
from the base metals
12
. Separations of zinc, cadmium, mercuary and bismuth has
been achieved using n-octylaniline as a extractant from hydrochloric acid media 13.
Objectives
Preconcentration of the elements of interest may prove sometimes to very
useful and advantageous. Enrichment of platinum group metals from matrix of natural
samples by using high molecular weight aniline as an extractant is well known. In
these research investigations we wish, to develop a solvent extractions procedure for
platinum metals from associated elements like base metals and preconcentrations of
these metals.
The extractant like N-n-heexylaniline is recently used for extraction
separations studies of bismuth and is works as liquid anion exchangers. It is cheep and
can be regenerated for reuse. The method can be applied at low acid concentrations in
moderately weak chloride medium. Most of base metals are present in cationic form
in the solutions where as platinum group metal complexes are stable at fairly low
chloride concentrations and hence separations of platinum group will be achieved.
Methodology
The liquid anion exchanger has a potential to separate selectively
precious group metals from the large concentration of flux and matrix elements. It
accommodates the relatively large volume of solution, which results from dissolution
of peroxide cake. The solvent extraction using liquid anion exchanger such as N-nhexyaniline will be carried out in batch extraction. The solution of platinum group
metals will be adjusted to low concentration at this stage these metals forms stable
anionic chlorocomplexes while the base metals remains quantitatively in aqueous
solution in the cationic form and hence separation will be achieved. The platinum
group metals extracted with reagent stripped with suitable strippands and determined
by spectrophotometric method. The procedure will be developed and condition will be
optimized for maximum separations of platinum group metals. After development of
these separation methods, it will be applied for the separation of platinum group
metals from real samples.
Techniques to be used in study:
Solvent extractions has becomes a very powerful method for separations. It is
very simple, rapid and selective. This method does not need any sophisticated
instrument, only separating funnel is used to carry out the separations. N-nhexylaniline will be used as a liquid anion exchanger for the study. The greeter
advantages of liquid anion exchanger is that one should regenerated liquid anion
exchanger and reuse it again after distillations N-n-heylaniline will be prepared
according to recommended procedure14. A solution (3:1 molar ratio) of distilled
aniline and n-hexylbromide was refluxed overnight after cooling to room temperature
the reaction mixture made basic with dilute aquous ammonia. Aqueous layer washed
with pentane and treated with 50% aqueous zinc chloride solution. Resulting solutions
is extracted with pentane dried over anhydrous potassium carbonate. Pentane is
removed by flash evaporations and resulting N-n-hexyalaniline obtained by fractional
distillations. The N-n-hexylaniline has a boiling point 145/16 mm and yield is 87%.
The individual platinum group metals will be adjusted to different molarities
with strong acids, weak acids and different pH at constant volume. These aqueous
solutions will be equilibrated with N-n-hexylaniline solutions in various organic
solvents. After extractions of metal ions with N-n-hexylaniline in organic solvents it
will be back stripped with water or different aqueous solutions and finely metal ion
will be determined in aqueous solutions using the standard spectrophtometric method.
In this study optimum conditions for quantitative extractions of metal ions
different parameter will be studied viz N-n-hexylaniline concentrations, acid
concentrations, pH, different stripping agents, equilibrations time and maximum
loading capacity of respective concentrations of N-n-hexylaniline. After development
of method for extraction of metals ions it will be applied for separation of platinum
group metals from each other and separation of metals from real samples.
Significance:
¾ The cost of chemical required for synthesis of extractant i.e. N-n-hexylaniline
is low and it will be prepared in the laboratory.
¾ Reagent will be reuse after regenerations without loss of efficiency.
¾ The proposed method will be simple and rapid.
¾ The proposed method will be effective for quantitative extraction of platinum
metals.
Reference
1. http//www.En.Wikipedia.org/wiki/precious-metal-32K.
2. http//www.education.jlab.org/itselemental/ele046.html.
3. R. B. Throat, A. S. Burungale, N. B. Kadam Patil. Rasayan.J. Chem., 2(1)
(20009) 1.
4. R. N. Gedye, J. Bozic, P. M. Durbanu and William Son., Talanta., 36(10)
(1989) 1055.
5. T.N.Lokhande, M.A.Anuse,M.B.Chavan,Talanta, 46 (1998) 163.
6. B.M.Sargar and M.A.Anuse,Talanta, 55(3) (2001) 469.
7. S. S. Kolekar and M. A. Anuse, Talanta., 58 (2002) 761.
8. T. N. Lokhande, M. A. Anuse, M. B. Chavan, G. B. Kolekar, Sep. Sic. Tech,
36(1) (2000) 153.
9. H.R.Aher, P.S. Gunjal, S.R.Kuchekar, Asian J. of Chem., 10, No.1 (1998) 43.
10. T.N.Lokhande, M.A.Anuse, S.H. Gaikawad, M.B.Chavan.Annali dichimica.,
92 (2002) 615.
11. S.S.Kolekar, and M.A.Anuse, Gold Bulletin, 34(2) (2001) 50.
12. T.N.Lokhande, M.A.Anuse, M.B.Chavan. J.Saudi,Chem.Soc.,4 (1) (2000) 1.
13. S. R. Kuchekar, H. R. Aher and M. B. Chavan, Ind. J. Chem., 42(2003) 1674.
14. Z. G. Gardlund, R. J. Curtis and G. W. Smith, Liq. Crystals and Orderd
Fluids., 2(1973) 541.