Efficient Removal of Cr^3+, Pb^2+ and Hg^2+ Ions from Industrial Effluents by Hydrolyzed/Thioamidated Polyacrylonitrile Fibres

Polyacrylonitrile fibres were chemically modified by conversion of their nitrilegroups into other effective adsorbent groups under a two-step process. At first,the modification process was initiated through hydrolysis of the fibres in analkaline solution. In the next step, functionalization of the fibres was carried forward bythiourea. The evolved surface characteristics and surface reactions were investigatedby elemental analysis, scanning electron microscopy and thermal gravimetry analysis.The modified polymer-metal complexes were obtained in aqueous solutions at differentpH media of 2 to 8. The experimental data were analyzed in terms of Langmuirisotherm model. The adsorption capacities of the samples towards Cr^3+, Hg^2+ and Pb^2+were in the given order of 0.73, 0.09, and 0.14 mmol/g (at pH 4). These results may beconsidered as an indication of higher selectivity of the modified fibres towards Cr^3+ ionscompared to Hg^2+ and Pb^2+ ions. The study on these modified ion exchange fibres(HTPANFs) for industrial effluents revealed that the maximum capacities of themodified PAN fibres towards Cr^3+, Hg^2+ and Pb^2+ are 0.41, 0.05, and 0.11 mmol/g (atpH 4), in the given order. The FTIR spectra of the modified fibre-metal complexesexhibited wavenumber shifts due to metal complex formation compared with the FTIRspectrum of just the modified fibres. The thermogravimetric data indicated that theinitial thermal stability of the modified fibres is lower than those of raw fibres due toconversion of nitrile groups into amine and thioamide functionalities.