Browsing by Subject "Kaolinit"

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Removal of organic and inorganic pollutants from aqueous solutions by organically modified clayey sediments
(2012) Mubarak, Dalia Mohamed Fahmy; Müller, Torsten
Re-use of agricultural drainage water and industrial wastewater is one of the adopted strategies in different countries to close the gap between water resources and water demands. Drainage and industrial wastewater contain varieties of toxic pollutants that can potentially cause hazard on humans and environment. Although adsorption techniques are considered one of the proper methods for the wastewater treatments, economic aspect is a crucial factor for the broad application of such technique. Addressing this, the thesis concerns on proposing sorbents having the potential to remove heterogeneous pollutants simultaneously, particularly taken in consideration the limited resources in developing and emerging countries, in this study exemplified for Egypt. For this purpose, natural clayey sediments as cheap and environmentally friendly materials were used in combination with various organic modifiers to produce of organically modified clayey sediments (OMCs). In contrast to the natural clayey sediments, OMCs are expected to have the ability to remove heterogeneous pollutants including anionic and cationic as well as organic and inorganic pollutants. The sorbability and desorbability characteristics of OMCs were investigated for Cd2+ and Pb2+ (cationic ), Cr2O72- (anionic-) and metalaxyl m (MM; organic-pollutants). The basic clay materials in OMCs were naturally occurring kaolinitic (kao sediment) and bentonitic (bent sediment) clayey sediments distributed widely in Egypt. Different concentrations of the organic modifiers L-Carnitine (Carnitin), L Cystine dimethyl ester (Cys_ester), Methyltriphenyl-phosphonium (MTP) or Hexadecyltrimethyl-ammonium (HDTM) were employed. The modification of natural clayey sediments with organic modifiers increased the organic carbon contents of OMCs following the order Carnitin < Cys_ester < MTP < HDTM. OMCs based on bent sediments had a higher loading of the organic modifiers than those based on kao sediments and the loading increased with increasing the used concentrations of the organic modifiers. To characterize and confirm the modification of OMCs, the prepared materials were analyzed by mid infrared spectroscopy (MIRS). The obtained spectra showed shifting of the vibration bands of the natural clayey sediments, and depicted the characteristic vibrations bands of the organic modifiers, indicating the interaction between the natural clayey sediments with the organic modifiers and the successful loading. Further analysis by X ray diffraction showed that the modification of OMCs based bent sediments with MTP or HDTM caused an expansion of the interlayer spacing of the clay from 14.5 Å to 17.1 or 19.7 Å, respectively; reflecting a bilayer or pseudo-trimolecular arrangements of MTP or HDTM, respectively, in the clays interlayer. The loading ratios of the organic modifiers on OMCs as a percentage of the CEC of the natural clayey sediments were also calculated. Following the characterization of OMCs, screening experiments were conducted to select the suitable concentration of each organic modifier to be loaded in order to achieve the highest removal of heavy metals. The results showed that loading of OMCs based on kao sediments by HDTM and Carnitin at concentrations equal to or higher than 71and 8 % of the CEC of the natural kao sediment, respectively, caused no relevant differences in the sorption of Cd2+ and Pb2+ compared to natural kao sediment. However, the loading of Cys_ester and MTP at concentrations equal to 38 and 21 % of the CEC or higher increased the sorption of those metal ions. Remarkable enhancements in the sorption of Cr2O72- were obtained by the modification of OMCs based kao sediments with HDTM and Cys_ester. The outcome from these screening experiments with OMCs based bent sediments can be concluded as follow: HDTM and MTP at loading concentrations > 50 % of the CEC of the natural bent sediments were able to remove all Cd2+ and Pb2+ from the solutions. However, increasing the loading concentration of Cys_ester decreased the sorption of those metal ions as compared to natural bent sediment. OMC modified with Carnitin at loading concentration up to 21 % of the CEC was able to remove 84 % of Cd2+ and 100 % of Pb2+ from the solutions but a further increase of Carnitin loading decreased the sorption of the metal ions. The OMCs modified with HDTM and Cys_ester were very efficient in removing Cr2O72- from the solutions and the removal increased with increasing loading concentrations of the organic modifiers. The OMCs based on bent sediments loaded with HDTM, MTP, Carnitin and Cys_ester at loading concentrations equal to 102, 79, 18 and 66 % of CEC of the natural bent sediments, respectively, and in addition OMC loaded with Humic acid (HA), were selected as promising sorbents to test the sorbability and desorbability of OMCs with respect to the pollutants. The sorption processes were investigated as function of the metal concentration, sorption time, the initial solution pH and the electrolyte concentration. OMCs modified with HDTM, MTP, HA and Carnitin showed high sorbability for Cd2+ and Pb2+. However, OMCs modified with Cys_ester displayed the best sorbent for Cr2O72-. OMCs were successful to remove almost all Cd2+, Pb2+ from the solutions at wide ranges of pH; 4-8 and 4-6, respectively, while the optimum for the sorption of Cr2O72- was pH 4. The Langmuir model described adequately the observed sorption data of Cd2+ and Pb2+ on all sorbents and Cr2O72- on OMC modified with Cys_ester better than the Freundlich model. The sorption followed the pseudo second order kinetics with the rate constants demonstrating faster sorption on OMCs with Carnitin and HA for Cd2+ and Pb2+ and faster sorption on OMCs with MTP and Cys_ester for Cr2O72-. Sorption of Cd2+ and Pb2+, particularly on OMCs with Carnitin and HA, were decreased with increasing electrolyte concentrations. Whereas, increasing the electrolyte concentrations enhanced the sorption of Cr2O72- to OMC with Cys_ester. OMCs showed ability to release the sorbed heavy metals, which shows the potential for re-using. The presence of other solutes in the binary and ternary component systems strengthened the sorption of Cr2O72- on OMCs based bent sediments with HDTM and MTP and enhanced the sorption of MM on OMCs with Cys_ester and MTP. Competition phenomena were recorded for the sorption of Cd2+ and MM on OMC with HDTM. No competition behaviours were observed in the sorption of the tested pollutants on OMC with Cys_ester. OMCs with HDTM, MTP and Cys_ester were able to remove Cd2+, Cr2O72- and MM simultaneously from the binary and ternary component systems. The results indicate the prospective application of the OMCs in the treatments of natural agricultural drainage water and industrial wastewater.