Аннотация:Supported ionic liquids (SIL) combine the advantages of ion exchange resins and liquid
extragents. Chemical attachment of ionic liquids’ molecules to solid support excludes the loss of
active component and allows to design new structures which are not possible in solutions. Here
we report a new route to SIL via chemical immobilization of a thin layer of short-chain
polyethyleneimine (PEI) molecules on silica surface, their crosslinking and quaternization with
methyl iodide or benzyl bromide and the use of sorbents thus obtained for extraction and
separation of platinum metal ions.
We employed for synthesis silica gels with specific surface area 300-400 m2/g and mean pore
diameter 10-15 nm, organosilicon compounds for chemical attachment of PEI molecules and
PEI with M.w. ~600, thus leading to sorbents with ~1-2 mmol/g content of active nitrogen
groups. Sorption experiments conducted in batch and column modes with Pd(II), Pt(II), Pt(IV),
Rh(III), Ir(III) and Ir(IV) ions, metal concentration varied in the range 0,01-10 g/l in HCl media
(0.1-6 M) with additional Cl- presence up to 100 g/l. Special emphasis we made on the elution of
sorbed platinum metals ions, here we tested a large set of eluents, including mineral acids,
solution of various salts (NaCl, NH4Cl, Na2SO3, etc.) and solutions of thiourea in HCl, under
ambient or elevated temperatures.
Sorption of platinum metals ions decreases with HCl concentration, but it is governed really by
chloride ions concentration. Binding of platinum metals ions with all sorbents studied proceeds
due to anion exchange mechanism, only in the case of Pd(II) sorption on unmodified PEI
sorbent complex formation was stated by diffuse reflectance and X-ray photoelectron
spectroscopy. Selectivity of binding depends rather on the charge and the size of platinum
metal chloride complex than on substituent on nitrogen moiety; affinity decreases in the raw
Pt(IV) > Ir(III) > Rh(III) ≈ Pd(II) > Ir(IV) > Pt(II) in 0.1 M HCl and in the raw Ir(III) > Pt(IV) ≈ Rh(III)
>> Pd(II) > Ir(IV) > Pt(II) in 6 M HCl. Pd(II) is effectively eluted by ammonia solution, Rh(III) and
Ir(IV) – by NH4Cl solution at 80oC, the same for Ir(III) after oxidation to Ir(IV) by chlorine water,
Pt(IV) is selectively eluted by thiourea-HCl solutions.
Sorbents studied are applied for separation of platinum metals from accompanying metals. e.g.,
copper and nickel, as well as for isolation of individual platinum metals from their mixtures.