125 Journal of Metallurgy and Materials Science, Vol. 56, No. 2, April-June 2014, pp. 125-135 Printed in India, © NML, ISSN 0972-4257 Studies on Pb(II) and Cd(II) adsorption by Fe(II) and Fe(III) silicate precipitation tubes in aqueous medium 1 K. PARMAR and S. BHATTACHARJEE 1 CSIR-National Metallurgical Laboratory, Jamshedpur-831007 Abstract : II III III tubes (Fe SPT and Fe SPT) in aqueous medium has been studied and reported. Fe SPT II is a better adsorbent than Fe SPT with reference to Pb(II) and Cd(II). Adsorption varies nonlinearly with initial concentration and adsorbent dose. Experimental adsorption data are modeled with Langmuir and Freundlich isotherms and isotherm parameters are obtained through regression of linearized isotherm equations as well as through direct and robust optimization of parent equations. Robust optimization always yields better fits as opposed to linear regression in terms of Sum Square Error (SSE) and goodness of 2 the fit (R ) between experimental and optimized model data. Pb(II) adsorption on both II III II Fe SPT and Fe SPT and Cd(II) adsorption on Fe SPT may be better represented by III Freundlich isotherm while Cd(II) adsorption on Fe SPT is more amenable to Langmuir form. Modifications to traditional Langmuir and Freundlich isotherms are proposed in which initial adsorbate concentration is introduced into the original form. The fit of II experimental data into the modified Langmuir form is remarkable. Both Fe SPT and III Fe SPT are identified with very high Pb(II) and Cd(II) loading capacities. Keywords : Adsorption, Lead, Cadimum, Iron, Precipitation, Robust optimization. INTRODUCTION Growth of self assembled hollow tree like structures emanating from the reaction between some metal salts and sodium silicate is popularly known as 'silica garden' reaction. These tubular structures are also called metal silicate precipitation tubes. Metal silicate precipitation tubes produced through 'silica garden route' is a genre of compounds known from an early date but not really looked upon seriously from an application perspective though there has been some advancement in this direction in recent times. Adsorption of heavy metal ions in aqueous medium is one such area where these compounds have shown [1-5] some promise . Historically first reporting of 'silica garden' reaction may be credited to Glauber about 350 years back when he observed growth of tree like structures during a reaction between FeCl and 2 [6] K SiO . Since then a number of metal ions have been reported to exhibit 'silica garden' 2 3 [3] [4] [5,6] [7,8] [9] reaction that include Ca(II) , Fe(III) , Fe(II) , Co(II) , Al(III) , Cu(II), Ni(II), Mn(II), [10-11] Mg(II) and Zn(II) . Though first 'silica garden' reaction was carried out with Fe(II) salts, inexplicably Fe(III) salts were kept out of the ambit of this reaction till recently. Fe(II) and Fe(III) silicate precipitation tubes produced through silica garden route have been characterized in detail and broadly [5] assessed for their heavy metal adsorption capability in aqueous medium . This communication aims to report in detail studies on Pb(II) and Cd(II) adsorption by Fe(II) and Fe(III) silicate precipitation tubes in aqueous medium. Central University of Jharkhand, Brambe, Ranchi-835205 Adsorption of Pb(II) and Cd(II) on Fe(II) and Fe(III) silicate precipitation