Use of aminoprophyl silica-immobilized humic acid for Cu(II) ions removal from aqueous solution by using a continuously monitored solid phase extraction technique in a column arrangement

Humic acid (HA) which originated from Leonardite was purified and immobilized onto aminoprophyl silica (APS). Afterwards, the remaining amino groups on the silica are successfully end-capped using acetic anhydride in DMF media and this material was used for Cu(II) ions removal from aqueous solution by using continuously solid phase extraction (SPE) technique in a column arrangement. The sorption characteristics of Cu(II)-immobilized humic acid (ImHA) system were investigated at various experimental conditions, and output was observed by a UV detector. All solid phase extraction (SPE) steps were monitored through breakthrough curves used to visualize distribution of Cu(II) concentration between mobile phase and solid phase. In addition to this, the solutions collected from stripping steps were analyzed in atomic absorption spectrophotometry (AAS) and the amount of adsorbed Cu(II) ions was calculated. It was found that there was a high correlation (R-2 = 1) between the peak area and AAS data of stripping steps. Sorption characteristics were evaluated by using Freundlich, Langmuir, and Dubinin-Radushkevich (D-R) adsorption isotherms, as well as by Scatchard plot analysis. Thus, the sorption characteristics and usability of ImHA as a solid phase for SPE of Cu(II) ions was evaluated in detail. From the obtained results, it was seen that sorption mechanism of Cu(II) fits to Langmuir model on a large scale, sorption was thought to be localized. From D-R isotherm mean free energy of sorption (E) was calculated (17.68 kJ mol(-1)), and it was deduced that chemical interactions were more effective than physical interactions for Cu(II). This investigation provides a new, environmentally friendly and cost-effective possibility to remove Cu(II) ions from aqueous solution by using the new APS-ImHA material. (c) 2007 Elsevier B.V. All rights reserved.