Ispitivanje mogućnosti modifikacije i katalitičkog potencijala industrijskih otpadnih ostataka u Fenton-procesu uklanjanja boje

Abstract

Cilj ove disertacije je ispitivanje katalitičkog potencijala različitih industrijskih, otpadnih ostataka (sojine ljuspice, papirni mulj, crveni mulj i filterski pesak) u heterogenom Fenton-procesu uklanjanja boje. Izvršene su dve vrste modifikacije početnih materijala, u zavisnosti od strukture i inicijalnog sadržaja Fe, i toimpregnacija jonima Fe(III) i termički tretman. Sprovedena je detaljna karakterizacija početnih materijala i pripremljenih katalizatora, zatim su određeni optimalni uslovi heterogene Fentonove reakcije primenom metode odzivnih površina, kao i evaluacija degradacije model polutanta (Reactive Blue 4 boje). Ultrazvukom potpomognuta impregnacija otpadnih sojinih ljuspica i papirnog mulja je doprinela inkorporaciji Fe u strukturu nosača, a kalcinacija katalizatora pri temepraturi od 350°C je dovela do degradacije prisutne celuloze kod oba materijala. Stoga, hemijska modifikacija je rezultovala katalizatorima povećane specifične površine, mezoporoznosti i konvertovanih jona Fe u kristale hematita. NJihovom primenom u oksidacionom procesu primećen je porast efikasnosti obezbojavanja (85,7 i 96,7%, redom), dok je ~66% RB4 boje mineralizovano. Stabilnost ovih katalizatora je bila na zadovoljavajućem nivou, gde je papirni mulj izdvojen kao superioran predstavnik stabilnog katalizatora u kiseloj sredini (izluženo je svega 0,002 mg Fe/l). Niska toksičnost efluenta (~20%) je ispitana kroz test inhibicije rasta Vibrio fischeri bakterija. Takođe, ponovna upotreba impregnisanih otpadnih ostataka ukazala je na blago smanjenje aktivnosti (~11%), što se može sanirati regeneracijom katalizatora. Otpadni crveni mulj i filterski pesak su termički tretirani (550°C) zbog poznatog prisutsva Fe na njihovim površinama. Karakterizacijom je primećena značajna razlika među njima, gde je crveni mulj bio sačinjen od sitnih, mezoporoznih čestica, sa kristalima hematita, a filterski pesak je imao krupniju granulaciju i značajno viši sadržaj Mn u odnosu na Fe što je verovatno uslovilo njegovu semi-kristalnu strukturu. Među njima, otpadni crveni mulj se pokazao aktivnim u heterogenom Fenton-procesu, sa efikasnošću obezbojavanja od 90,1%, i stabilnim u pogledu izluženog Fe (0,22 mg/l). Međutim, primećeno je i prisustvo Al u koncentracijama bliskim dozvoljenim graničnim vrednostima (~3 mg/l), što je verovatno doprinelo povišenoj inhibiciji rasta Vibrio fischeri bakterija (~35%). Sa druge strane, primenom otpadnog filterskog peska u oksidacionom tretmanu postignuto je umereno obezbojavanje vodenog rastvora RB4 boje, uz znatno više izluživanje Fe i dodatnog Mn u vodenu fazu. Dato sekundarno zagađenje je doprinelo izraženoj toksičnosti efluenta (73%), te se ne predlaže njegova dalja primena u Fenton-procesu. Pored odabranih otpadnih ostataka, ispitana je i modifikacija i primena komercijalno dostupnih materijala – Na-bentonita i Fe(III)-oksida. Smektitna glina je impregnisana jonima Fe(III), gde se pokazalastabilnom tokom kalcinacije. Pripremljen mezoporozni katalizator je bio veoma aktivan u degradaciji RB4 boje (94,0%) uz nisko izluživanje Fe, gde je udeo sorpcije bio ~10%. Sa druge strane, Fe2O3 je pokazao nezavidnu aktivnost ispod 20%), što je verovatno prouzrokovano veoma niskom specifičnom površinom (najmanja među svim ispitivanim katalizatorima). Na osnovu rezultata ove disertacije, izdvajaju se otpadni papirni i crveni mulj kao dva predstavnika aktivnih katalizatora heterogene Fentonove reakcije. Otpadni papirni mulj nakon ultrazvukom unapređene impregnacije je veoma stabilan katalizator, a njegova aktivnost je potpomognuta i simultanim odvijanjem sorpcionih reakcija. Crveni mulj, takođe, ima potencijal za primenu u oksidacionom tretmanu, s tim što je neophodno praćenje stabilnosti, uz poseban osvrt na izluživanje Al, ali i ostalih prisutnih elemenata u njegovoj strukturi. Tako bi se obezbedilo bezbedno i efikasno iskorišćenje industrijskog otpada.

The aim of this dissertation is to investigate the catalytic potential of various industrial waste residues (soybean hulls, paper mill sludge, red mud and filter sand) in the heterogeneous Fenton process of dye removal. Two types of modification of the initial materials were performed, depending on the structure and initial Fe content, namely impregnation with Fe (III) ions and thermal treatment. Detailed characterization of waste residues and prepared catalysts was performed, then the optimal conditions ofthe heterogeneous Fenton reaction were determined using the response surface methodology, as well as the evaluation of model pollutant (Reactive Blue 4 dye) degradation. Ultrasound assisted impregnation of waste soybean hulls and paper mill sludge contributed to the incorporation of Fe into the carrier structure, and the calcination of catalysts at 350°C led to the degradation of cellulose present in both materials. Therefore, the chemical modification resulted in catalysts with increased specific surface area, mesoporosity and converted Fe ions to hematite crystals. Their application in the oxidation process showed an increase in decolorization efficiency (85.7 and 96.7%, respectively), while ~66% of RB4 dye was mineralized. The stability of these catalysts was at a satisfactory level, where paper sludge was isolated as a superior representative of a stable catalyst in an acidic medium (only 0.002 mg Fe/L was leached). The toxicity of the effluent was also examined, through the test of Vibrio fischeri bacteria growth inhibition, which was low (~20%). Also, the reuse of impregnated waste residues indicated a slight decrease in activity (~ 11%), which can be remedied by catalyst regeneration. Waste red mud and filter sand were thermally treated (550°C) due to the known presence of Fe on their surfaces. The characterization showed a significant difference between them, where the red mud, was composed of small, mesoporous particles with hematite crystals, while the filter sand had a larger granulation and significantly higher Mn content compared to Fe, which probably conditioned its semi-crystalline structure. Among them, waste red mud proved to be active in the heterogeneous Fenton process, with a decolorization efficiency of 90.1%, and stable in terms of leached Fe (0.22 mg/L). However, the presence of Al was also observed in concentrations close to the permitted limit values (~3 mg/L), which probablycontributed to the increase in the inhibition of Vibrio fischeri bacterial growth (~35%). On the other hand, with application of waste filter sand in the oxidation treatment moderate discoloration of the aqueous solution of RB4 dye was achieved, with significantly higher leaching of Fe and additional Mn into the aqueous phase. The given secondary pollution contributed to the pronounced toxicity of the effluent (73%), and its further application in the Fenton process is not proposed. In addition to selected waste residues, the modification and application of commercially available materials (Na-bentonite and Fe(III)-oxide) were investigated. Smectite clay was impregnated with Fe (III) ions, where it proved to be stable during calcination. The prepared mesoporous catalyst was very active in the degradation of RB4 dye (94.0%) with low Fe leaching, where the sorption fraction was ~10%. On the other hand, Fe2O3 showed unenviable activity (below 20%), which is probably caused by a very low specific surface area (the lowest among all tested catalysts)Based on the results of this dissertation, waste paper mill sludge and red mud are singled out as two representatives of active catalysts for the heterogeneous Fenton reaction. Waste paper mill sludge after ultrasonic impregnation is a very stable catalyst, and its activity is supported by the simultaneous occurrence of sorption reactions. Red mud also has the potential for application in oxidative treatment, but it is necessary to monitor its stability, with special reference to the leaching of Al, and also other elements present in its structure. This would ensure the safe and efficient use of industrial waste.