Characterization and Applications of Poly‐Acetate Modified Silica Polyamine Composites

Abstract

Silica polyamine composites made from silanized amorphous silica gel and a polyamine (polyallylamine (BP‐1) and poly(ethyleneimine) (WP‐1)) were functionalized with ethylenediamine‐N,N,N′,N′‐tetraacetic (EDTA) anhydride resulting in the modified composites BP‐ED and WP‐ED respectively. Successful immobilization of the poly‐acetate ligand was confirmed by weight gain, IR and elemental analysis. The modified composites had ligand loading values of 0.78 mmol/g and 0.58 mmol/g respectively. Adsorption characteristics were investigated for BP‐ED and WP‐ED by pH profiles, time dependent isotherms, concentration dependent isotherms, and the Langmuir and Freundlich adsorption models. Metal ion capacities (mmol of metal adsorbed per gram of adsorbent) were shown to increase with pH for BP‐ED and WP‐ED, which is in contrast with silica gel modified with EDTA anhydride via amino propyl silane without the use of a polyamine where the opposite trend is observed. The adsorption of Ni(II), Zn(II) and Co(II) onto BP‐ED and WP‐ED was shown to fit the Langmuir adsorption model, which indicates a monolayer, non‐cooperative metal ion uptake. For both composites the divalent metal ion selectivity is as follows: Cu(II)>Ni(II)>> Zn(II), Co(II)>> Mn(II). Also the trivalent metal ion selectivity is as follows: Fe(III)>Ga(III)>> Eu(III)>Al(III). This is in close agreement with reported formation constants for EDTA in solution. Breakthrough and recovery tests were carried out using a 5cc packed column. The separation and recovery of Ni(II) from Co(II) when BP‐ED was challenged with a solution containing 1.5 mg/L of both metals resulted in an acidic strip solution of greater than 97% Ni(II) purity. Further, selective separation of Ni(II) from a solution containing low levels of Co(II) and Zn(II) and high level Fe(II) at pH=1 was also achieved. Ni(II) was extracted at a flow rate of 0.1 column volumes per minute (0.5 mL/min) and recovered in greater than 90% purity by an acidic strip. Impurity in the strip was a consequence of Fe(II) oxidation to Fe(III). These tests demonstrate that well resolved separations of one divalent metal ion from one or more other divalent metal ions are possible through the use of EDTA anhydride modified silica polyamine composites with higher capacities than the previously reported amino propyl silane modified silica gel.