Abstract
To investigate the efficacy of modified clay minerals to remediate heavy metals from industrial wastewater, two natural clay sediments dominated by kaolinite were selected. Since the kaolinite clay has low cation exchange capacity, some modifications were made using unusual treatments thermal transformation and acid activation techniques were used to increase exchangeability properties for producing modified kaolinite. The increased exchangeability was demonstrated through various methods. Results of X-Ray diffraction analysis verified the transformation of Kaolinite as indicated from disappearing all the diffractogram peaks due to kaolinite. In infra-red spectroscopy, the presence of a broad band with little change in the intensity in the region coupled with broad Si-O bending vibration band and Si-O-Al compound vibration bands explain the extent of structural disorder as a response of modification treatment. From a mineral structural viewpoint, destruction through heat treatment exposes directed -OH bonds located between the tetrahedral and octahedral layers (amorphization). It has been observed that after an acidification treatment, the -OH groups become less stable and lead to the newly formed vacant sites during the modification treatments accommodate extra structural water; thereby; broadening the -OH bands in the I.R spectrum.
Scanning Electron Microscope study has clearly demonstrated that, transformation in kaolinite structure from from hexagonal original shape to edgeless shape and values of Cation Exchange Capacity C.E.C were increased from 8.2 to 18.41 Meq/100g and from 12.66 to 28.53 Meq/100g in both Sinai and Aswan sediment, respectively. Result of the present study has indicated that crystalling structure of kaolinte tranformed to collapsed structure after modification treatment and the new structure can absorb a large amounts of pollutant metallic ions including Zn and cu from wastewater.
Observed increase of metal ions removed by modified clays are due to increase of exchange sites produced by the acid leaching on a collapsed kaolinite framework. A comparison of relative removing values between Zn and Cu revealed that the removing kinetics of Cu is more favored under identical molar concentrations than Zn.