Removal of toxic ions from aqueous solutions using modified cellulose-based adsorbents

[J. Perendija]

127 str.

Hemijske nauke - Analitička hemija / Chemistry - Analytical chemistry

Predmet istraživanja ove doktorske disertacije je modifikacija celuloznih materijala kao adsorbenata za efikasno uklanjanje toksičnih jona iz vodenih rastvora. Modifikacija površine celuloze i prisustvo funkcionalnih grupa sa višim nivoom afiniteta prema toksičnim jonima veoma su važni za unapređenje adsorpcionih svojstava. U okviru ovog rada dobijena su dva različita tipa adsorbenta na bazi celuloze koji su odgovarajućim tehnikama formirani u obliku membrane. Prvi tip membrana je na bazi celuloze modifikovane magnetitom, dok su drugi tip bio-membrane na bazi modifikovane celuloze, lignina i taninske kiseline. U prvom slučaju, primenjena je optimizovana metoda za izradu magnetit (MG) modifikovane celulozne membrane (Cell-MG hibridne membrane) na bazi amino silanom funkcionalizovanog otpadnog celuloznog vlakna (Cell-NH2) i dijatomejske zemlje (D-APTES), kao i Cell-NH2 modifikovane dianhidridom dietilentriamin-pentasirćetne kiseline (Cell-DTPA). Drugi tip membrane dobijen je na osnovu dve optimizovane metode, zasnovane na reaktivnosti između amino grupa celuloznih vlakana (Cell), modifikovanih u prvom koraku sa 3-(karbometoksi) propionil-hloridom (CPC) i dietilentriaminom u drugom koraku (Cell-DETA), sa epoksi grupama Cell vlakana modifikovanih 3-glicidoksipropiltrimetoksi silanom (Cell-Glymo) i lignina modifikovanog epihlorohidrinom (EL). Taninska kiselina korišćena je kao dodatni umreživač. Dobijene bioobnovljive membrane označene su kao Cell-EL i Cell-EL-TA. Celulozna vlakna, funkcionalizovani materijali i membrane okarakterisani su određivanjem mehaničkih svojstava, termogravimetrijskom analizom, infracrvenom spektroskopijom sa Furijeovom transformacijom, Ramanovom spektroskopijom, rendgenskom difrakcionom analizom, skenirajućom elektronskom mikroskopijom sa emisijom polja i softverskom analizom slike. Određena je poroznost membrane i veličina pora, ravnotežni stepen bubrenja, tačka nultog naelektrisanja (pHpzc), sadržaj amino grupa, kiselinski i epoksidni broj. Metoda odzivnih površina primenjena je kako bi se racionalizovao broj eksperimenata povezanih sa sintezama Cell-MG hibrid, Cell-EL i Cell-EL-TA membrana. Ista metoda primenjena je za optimizaciju eksperimenata povezanih sa adsorpcijom teških metala u protočnom sistemu upotrebom Cell-MG hibrid membrane. Uticaj pH vrednosti, kontaktnog vremena, temperature, doze adsorbenta i početne koncentracije zagađujućih supstanci na adsorpciju i kinetiku proučen je u šaržnom, dok je uticaj početne koncentracije i brzine protoka proučen u protočnom sistemu. Izračunati maksimalni adsorpcioni kapacitet Cell-MG hibrid membrane u uklanjanju nikla, olova, hroma(VI) i arsena(V) primenom Lengmirovog modela iznosio je 88,2, 100,7, 95,8 i 78,2 mg·g-1. Primenom Lengmirovog modela izračunate su sledeće vrednosti kapaciteta: 53,9, 99,9, 97,8 i 63,5, 115,8, 127,5 mg·g-1 za nikl, olovo i hrom(VI), redom, koristeći Cell- EL, odnosno Cell-EL-TA. Termodinamički adsorpcioni parametri za Cell-MG hibrid, Cell-EL i Cell-EL-TA membrane ukazali su na spontane i endotermne procese. Kinetika adsorpcije najbolje se može opisati modelom pseudo-drugog reda, dok rezultati dobijeni primenom Veber-Morisovog modela ukazuju da unutarčestična difuzija kontroliše ukupnu brzinu procesa adsorpcije. Velika pažnja posvećena je unapređenju efikasnosti regeneracije sa ciljem povećanja perioda eksploatacije, pa je stoga izvršena optimizacija regeneracije membrana u odnosu na parametre desorpcije kao što su tip regeneratora, koncentracija i vreme rada. Osim moguće višestruke upotrebe membrana u adsorpciono-desorpcionim ciklusima, da bi otpadna voda iz ciklusa adsorpcije/desorpcije dostigla fizičko-hemijska svojstva koja odgovaraju propisanim vrednostima, primenjen je tretman efluenta precipitacijom. Razvoj efikasne tehnologije regeneracije obezbedio je adsorbent visokih kapaciteta, primenjiv u procesima prečišćavanja voda. Eksperiment određivanja toksičnih karakteristika adsorbenta (Cell-EL i Cell-EL-TA) nakon korišćenja (TCLP test) izveden je sa ciljem potvrde validnosti upotrebe membrana u adsorpciono-desorpcionim ciklusima i njihovog sigurnog odlaganja na deponije. Rezultati TCLP testa kao glavni kriterijumi za manipulaciju membranom i za njenu moguću primenu u uklanjanju toksičnih zagađujućih supstanci, dokazali su na osnovu utvrđenog sadržaja metala u membranama, da se istrošeni adsorbent može sigurno odložiti kao ekološki prihvatljiv materijal. Na ovaj način su rešena glavna pitanja odlaganja iskorišćenih membrana, usled biorazgradivosti upotrebljene membrane, efikasnosti desorpcije i razvoja tehnologije za tretman efluenta uz bezbedno odlaganje zaostalih nusproizvoda. Kako bi se opisala veza između performansi adsorpcije i doprinosa nespecifičnih i specifičnih interakcija između adsorbata i Cell-MG hibrid membrane, ispitan je kapacitet uklanjanja četiri boje, pri čemu su dobijeni rezultati detaljno analizirani primenom teorije funkcionala gustine (DFT) zajedno sa proračunima molekulskog elektrostatičkog potencijala i polja molekulskih interakcija. Značajan doprinos disertaciji ostvaren je poluempirijskim kvantno-hemijskim propračunima koji su pomogli u analizi nespecifičnih i specifičnih interakcija između Cell-EL i Cell-EL-TA adsorbenta i adsorbata i njihovom doprinosu ukupnom mehanizmu vezivanja. Adsorpciona studija u protočnom sistemu sprovedena je da bi se razmotrila moguća primena Cell-MG, Cell- EL i Cell-EL-TA membrana u kontinuiranim procesima prečišćavanja voda. Za predviđanje dinamičkog ponašanja membrana u koloni, primenjeni su Bohart-Adamsov, Jun-Nelsonov, Klarkov i Modifikovani model doza-odziv. Podaci dobijeni upotrebom primenjenih modela pokazuju dobro slaganje sa eksperimentalnim rezultatima za sve proučavane parametre procesa, ukazujući na to da su modeli bili pogodni za dizajn kolone sa fiksnim slojem upotrebom Cell-MG hibrid, Cell-EL i Cell-EL-TA membrana. Predstavljeni rezultati pokazali su primetan adsorpcioni učinak ovih membrana u protočnom sistemu sa visokim potencijalom u prečišćavanju voda. U cilju procene performansi dobijene membrane su testirane u šaržnom sistemu korišćenjem model vode napravljene prema podacima nađenim za rudničke otpadne vode. Pokazalo se da dobijene membrane nemaju visoku selektivnost, ali da poseduju visoku efikasnost u uklanjanju katjona i oksianjona iz otpadnih voda. Dobijeni rezultati na laboratorijskom nivou potvrdili su njihovu potencijalnu primenljivost u procesu prečišćavanja otpadnih voda sa visokom koncentracijom zagađujućih supstanci. Poređenjem efikasnosti procesa adsorpcije i maksimalnih adsorpcionih kapaciteta adsorbenata na bazi modifikovane celuloze sa rezultatima objavljenim u literaturi, pokazano je da dobijene membrane imaju unapređenu sposobnost adsorpcije.

The research subject of this doctoral dissertation is the modification of cellulose materials as adsorbents for efficient removal of toxic ions from aqueous solutions. Modification of the cellulose surface and the presence of functional groups with a higher level of affinity for toxic ions, are very important for improving the adsorption properties. Within this work, two different types of cellulose-based adsorbents were produced in the form of a membrane by appropriate techniques. The first type of membrane is based on magnetite modified cellulose, while the second type of bio-membrane is based on modified cellulose, with the addition of lignin and tannic acid. An optimized method for the production of magnetite (MG) modified cellulose membrane (Cell-MG hybrid membrane), based on amino-silane functionalized waste cellulose fiber (Cell-NH2) and diatomaceous earth (D-APTES) was applied, as well as Cell- NH2 modified with diethylenetriaminepentaacetic acid dianhydride (Cell-DTPA). The second type of membrane was obtained by two optimized methods, based on reactivity between amino groups of cellulose fibers (Cell), modified in the first step with 3-(carbomethoxy)propionyl chloride (CPC) and diethylenetriamine in the second step (Cell-DETA), with epoxy groups of Cell fibres modified with 3-glycidoxypropyltrimethoxy-silane (Cell-Glymo) and epichlorohydrin (EL) modified lignin. Tannic acid was used as an additional crosslinker. The obtained biodegradable membranes were marked as Cell-EL and Cell-EL-TA. Cellulose fibers, functionalized materials and membranes were characterized using determination of mechanical properties, Thermogravimetric analysis, Fourier-Transform Infrared Spectroscopy, Raman spectroscopy, X-Ray Difraction, Scanning Electron Microscopy, and with Image analysis software. The membrane porosity and pore size, the equilibrium-swelling ratio, the point of zero charge (pHpzc), the content of amino groups, acid and epoxy number were determined. The Response Surface Method (RSM) was applied to rationalize the number of experiments related to the synthesis of Cell-MG hybrid, Cell-EL, and Cell-EL-TA membranes. The same method was applied to optimize heavy metal adsorption experiments in a flow system using a Cell-MG hybrid membrane. The influence of pH, contact time, temperature, adsorbent dose and initial concentration of pollutants on adsorption and kinetics was studied in a batch, while the influence of initial concentration and the flow rate was studied in a flow system. The calculated maximum adsorption capacity of the Cell-MG hybrid membrane in the removal of nickel, lead, chromium(VI) and arsenic(V) using the Langmuir model was 88.2, 100.7, 95.8 and 78.2 mg·g-1. Using the Langmuir model, the following capacity values were calculated: 53.9, 99.9, 97.8 and 63.5, 115.8, 127.5 mg·g-1 for nickel, lead and chromium (VI), using Cell- EL and Cell-EL-TA, respectively. Thermodynamic adsorption parameters for Cell-MG hybrid, Cell-EL and Cell-EL-TA membranes indicated spontaneous and endothermic processes. The adsorption kinetics can best be described by a pseudo-second order model, while the results obtained using the Weber-Morris model indicate an intra-particle diffusion as a rate-limiting step. Great attention was paid to improving the regeneration efficiency in order to increase the period of exploitation, and therefore the optimization of membrane regeneration was performed concerning desorption parameters such as regenerator type, concentration and operating time. In addition, to achieve satisfactory reusability of membranes, wastewater from the adsorption/desorption cycle need to reach physicochemical properties corresponding to the prescribed values, hence the effluent treatment by precipitation was applied. The development of efficient regeneration technology has provided a high-capacity adsorbent, applicable in water purification processes. An experiment to determine the toxic properties of the adsorbent (Cell-EL and Cell-EL-TA) after use (TCLP test) was performed to confirm the validity of the membranes used in the adsorption-desorption cycles. The results of the TCLP test, as the main criteria for membrane manipulation and its possible application in the removal of toxic pollutants, based on the determined metal content in the membranes, proved the spent adsorbent can be safely disposed of as environmentally friendly material. Thus, the main issues of biodegradability of the used membrane, efficiency of desorption and development of technology for effluent treatment with safe disposal of residual by-products are solved. To describe the relationship between adsorption performance and the contribution of nonspecific and specific interactions between adsorbate and Cell-MG hybrid membrane, the four-colour removal capacity was examined, along with Density-functional theory (DFT) and calculations of molecular electrostatic potential and molecular interaction fields. A significant contribution to the dissertation was made by semi-empirical quantum-chemical calculations helped in the analysis of nonspecific and specific interactions between Cell-EL and Cell-EL-TA adsorbent and adsorbate and their contribution to the overall binding mechanism. An adsorption study in the flow system was conducted to consider the possible application of Cell-MG, Cell-EL and Cell-EL-TA membranes in a continuous water purification processes. To predict the dynamic behaviour of the membranes in the column, Bohart-Adams, Jun-Nelson, Clark and a Modified dose-response model were applied. The data obtained using the applied models show good agreement with the experimental results for all studied process parameters, indicating that the models were suitable for the design of a fixed-bed column using Cell-MG hybrid, Cell-EL and Cell-EL-TA membranes. The presented results showed a noticeable adsorption effect of these membranes in a flow system with a high application potential in water purification. Additionally, to evaluate the performance, the obtained membranes were tested in a batch system using model water made according to data found for real mining wastewater. It was shown that the produced membranes do not have high selectivity, but they have high efficiency in removing cations and oxyanions from wastewater. The obtained results at the laboratory level confirmed membrane potential applicability in the process of wastewater treatment, with a high concentration of pollutants. Comparison of the efficiency of the adsorption processes and the maximum adsorption capacities of the adsorbents based on modified cellulose with the results published in the literature, showed improved adsorption capacity of the produced membranes.

celulozna membrana, magnetit, lignin, taninska kiselina, šaržna i protočna adsorpcija, toksični joni, poluempirijski proračuni, održivi razvoj

cellulose membrane, magnetite, lignin, tannic acid, batch and flow adsorption, toxic ions, semi-empirical calculations, sustainable development

543.215/.216:66.021.3.081.3(043.3)

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