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A new and highly effective adsorbent has been synthesized through immobilization of Cd(II) protected active sites of humic acid (HA) on chitosan (Chit) using glutaraldehyde (Glu) cross-linker and followed by elution of the Cd(II) protector from the produced material by using Na2EDTA. The adsorbent (Chit-Glu-Cd-HA) was then utilized to adsorb Cd(II) in an aqueous solution. The stability of the Chit-Glu-Cd-HA adsorbent towards dissolution at various aqueous medium acidities was the best if compared to the stability of adsorbents obtained through direct immobilization of unprotected HA on chitosan (Chit-HA) and through the glutaraldehyde assisted immobilization of the unprotected HA on chitosan (Chit-Glu-HA). Within the medium acidity range from pH 2 to 12, the dissolved AH from the synthesized Chit-Glu-Cd-HA adsorbent was < 2.1 %(w/w), while that from Chit-Glu-HA and Chit-HA was < 11.2 and 20.1 %(w/w), respectively. For the Chit-Glu-Cd-HA adsorbent, every g of adsorbent contained 497 mg of AH. On the other hand, AH contained in every g of Chit-HA and Chit-Glu-HA was remarkably lower, i.e. 30 and 291 mg, respectively. With 80 % degree of Cd(II) elution from the Chit-Glu-Cd-AH by using Na2EDTA 0.05 M, the maximum adsorption ability of the adsorbent for Cd(II) was 5.67 x 10 mol/g and this capacity was significantly higher compared to that of Chit-HA and Chit-Glu-HA, i.e. 1.67 and 0.41 x 10 mol/g, respectively. These adsorption capacity data may indicate that glutaraldehide utilized to immobilize unprotected HA on chitosan consumes the active site of the formed adsorbent. The protection of active sites of HA with Cd(II) before immobilization to chitosan using glutaraldehyde releases the active sites of HA from their obligation to interact with glutaraldehyde and therefore after eluting the Cd(II) protector, the active sites of the immobilized HA are available to be occupied by Cd(II) adsorbed from the aqueous solution.

Immobilization of Active Site Protected Humic Acid on Chitosan as High Performance Adsorbent for Cd(II)