Abstract
Calcium carbonate (CaCO3) was synthesized in the presence of the water-soluble biopolymer carboxymethyl inulin (CMI) by a precipitation method. The obtained CaCO3 crystals were characterized by X-ray diffraction (XRD) and Scanning Electron Microscopy (SEM). The results showed that the polymorph of the synthesized calcium carbonate crystals changed from pure calcite to the mixture of vaterite and calcite in the presence of biopolymer at a concentration of 0.5 g/L. The sorption behavior of Cu(II) on synthesized calcium carbonate crystals was investigated. The results showed that Cu(II) sorption rate was fast and most of Cu(II) was adsorbed within 5 minute. The experimental results were fitted to the modified Freundlich, pseudo-first-order, and pseudo-second-order equations to find out sorption capacities. The results indicate that the sorption data fits well in the modified Freundlich isotherm model. This indicates the existence of multiple sites available for adsorption.
Introduction
Waste waters consisting of heavy metals ions have permanent toxic effect. Chemical precipitation, ion exchange, adsorption, membrane separation and electrodialysis can be used to remove heavy metals from waste.1-5 Although reverse osmosis, ion exchange and electrodialysis are proposed for dilute metal concentration with high removal efficiency, their operating cost is very high. Ionic-exchange with synthetic resins is not only an expensive method to remove heavy metals, but also operational costs of them create sludge disposal problems. In addition, the requirement of legislation for metal concentration can’t be suitable with these processes. Sometimes, precipitation does not meet of purifying water down to the legal limits. 6 Adsorption with the selection of proper an adsorbent can be used especially in the water treatment application. 5,7 Mineral adsorbents such as zeolites, 8 silica9 and organic adsorbent such as activated carbon, 10 coconut fiber11 and chitosan12 have been widely used in adsorption processes.
Calcium carbonate (CaCO3) has been used as an adsorbent for the removal of Cd,6, 13-14 Cr, 6 Mn-Fe, 15 Co14 and Zn. 14, 16 Sorption experiments have shown that divalent Co, Mn, Cd, Zn, and Ni cations are strongly adsorbed by the calcium carbonate surface. 17 The capacity of CaCO3 for retention heavy metals is very high. 14 CaCO3 is an essential adsorbent for metals in groundwater. Adsorption process can be affected by the reactions of metals at the solidsolution interface. A decrease in the adsorption rate follows the adsorption of metals at mineral-water interface. Natural adsorbents are not found as pure component in soil, so adsorption onto natural adsorbents is a complex procedure. 18 The sorption mechanism of calcium carbonate has not been understood well. 19
