The presence of Cr(VI) in waters represents a serious environmental problem, indeed it is recognized as a carcinogenic and mutagenic compound. The aim of this experimental thesis is to compare two processes for the removal of Cr (VI): adsorption and ion exchange. The tested materials are three granular activated carbons: two coconut-shell carbons (Acticarbone NCL 1240, AquaSorb CT) and a coal-based carbon (Cecarbon Gac 1240), and two strong-base anion resins type I chloride form (Resinex A-4, Purolite A600E/9149). The performances of the materials were evaluated by batch technique, determining adsorption kinetics and equilibrium isotherm using groundwater from the city of Milan. Pseudo first-order and pseudo second-order reaction models were calculated for the determination of kinetic parameters, than the isotherm experiments were described by the Freundlich and Langmuir model. The materials showed good removal efficiencies, around 90%. The resins have faster kinetics than the activated carbons and reach equilibrium in 3 - 4 hours. The coconut-shell carbon reaches equilibrium in 24 hours and the coal-based carbon in 48 hours. The pseudo first-order model well fitted the kinetic data with R2 > 0,9, for all the materials except for GAC-M, whose data were better simulated by pseudo second order model. For the resins the best model for equilibrium data was Langmuir, while none of the considered models adequately fitted the data for the activated carbons.The materials showed interactions with different compounds present in the groundwater (anions, metals and nonmetals). In particular, a significant removal of boron was observed (with average removal efficiency of 70% for coal-based carbon and 80-85% for coconut-shell carbons) while coal-based carbon showed a release of metals (Al and Fe), probably due to the numerous processes of regeneration. The resins showed a removal of some anions as sulfide with removal efficiency of 38-88% and nitrate of 25-57%.
La presenza di Cr(VI) nelle acque costituisce un grave problema ambientale, essendo un composto cancerogeno e mutageno. Il presente studio ha come obiettivo confrontare due processi per la rimozione di Cr(VI): adsorbimento e scambio ionico. I materiali considerati sono tre carboni attivi granulari di cui due vegetali (Acticarbone NCL 1240, AquaSorb CT) e uno minerale (Cecarbon Gac 1240), e due resine anioniche forti di tipo I in ciclo cloro (Resinex A-4, Purolite A600E/9149). Sono state eseguite prove batch per la determinazione di cinetiche e isoterme utilizzando acqua di falda della città di Milano per valutare le prestazioni dei materiali. Per la stima dei parametri cinetici sono stati utilizzati i modelli di pseudo primo e pseudo secondo ordine, invece, per i parametri dell’isoterma sono stati utilizzati i modelli di Freundlich e di Langmuir. I materiali presentano buone efficienze di rimozione, intorno al 90%. Le resine mostrano cinetiche più veloci rispetto ai carboni attivi e raggiungono l’equilibrio in 3-4 ore. I carboni vegetali raggiungono l’equilibrio in 24 ore e il carbone minerale in 48 ore. Il modello di pseudo primo ordine ha interpretato meglio i dati e presenta R2 >0,9 per tutti i materiali tranne che per GAC-M in cui il modello migliore è stato quello di pseudo secondo ordine. L’isoterma di Langmuir ha interpretato bene i dati d’equilibrio delle resine con R2> 0,9, mentre per i carboni nessuno dei modelli di isoterma considerati ha interpretano bene i dati (R2=0,342-0,702). I materiali hanno mostrato interazioni con i diversi composti presenti nell’acqua di falda (anioni, metalli e metalloidi). In particolare, si è osservata una contestuale rimozione di boro con i GAC (mediamente rendimenti del 70% per GAC-M e 80-85% per i carboni vegetali) e per il carbone attivo minerale un rilascio di metalli in soluzione (Al e Fe), diretta conseguenza nei numerosi processi rigenerativi cui è stato sottoposto. Le resine hanno rimosso alcuni anioni presenti come il solfato con efficienza tra 38 e 88% e il nitrato tra 25 e 57%.
Rimozione di Cr(VI) da acque di falda : confronto di prestazioni tra adsorbimento e scambio ionico
ROTA, FRANCESCA
2014/2015
Abstract
The presence of Cr(VI) in waters represents a serious environmental problem, indeed it is recognized as a carcinogenic and mutagenic compound. The aim of this experimental thesis is to compare two processes for the removal of Cr (VI): adsorption and ion exchange. The tested materials are three granular activated carbons: two coconut-shell carbons (Acticarbone NCL 1240, AquaSorb CT) and a coal-based carbon (Cecarbon Gac 1240), and two strong-base anion resins type I chloride form (Resinex A-4, Purolite A600E/9149). The performances of the materials were evaluated by batch technique, determining adsorption kinetics and equilibrium isotherm using groundwater from the city of Milan. Pseudo first-order and pseudo second-order reaction models were calculated for the determination of kinetic parameters, than the isotherm experiments were described by the Freundlich and Langmuir model. The materials showed good removal efficiencies, around 90%. The resins have faster kinetics than the activated carbons and reach equilibrium in 3 - 4 hours. The coconut-shell carbon reaches equilibrium in 24 hours and the coal-based carbon in 48 hours. The pseudo first-order model well fitted the kinetic data with R2 > 0,9, for all the materials except for GAC-M, whose data were better simulated by pseudo second order model. For the resins the best model for equilibrium data was Langmuir, while none of the considered models adequately fitted the data for the activated carbons.The materials showed interactions with different compounds present in the groundwater (anions, metals and nonmetals). In particular, a significant removal of boron was observed (with average removal efficiency of 70% for coal-based carbon and 80-85% for coconut-shell carbons) while coal-based carbon showed a release of metals (Al and Fe), probably due to the numerous processes of regeneration. The resins showed a removal of some anions as sulfide with removal efficiency of 38-88% and nitrate of 25-57%.| File | Dimensione | Formato | |
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https://hdl.handle.net/10589/120401