|Tipo di tesi||Tesi di dottorato di ricerca|
|Titolo||Sviluppo di tecnologie sostenibili per la valorizzazione di silice amorfa da rifiuti e sottoprodotti per diverse applicazioni|
|Titolo in inglese||Development of sustainable technologies for valorization of amorphous silica from waste and by-products for different applications|
|Settore scientifico disciplinare||CHIM/07 - FONDAMENTI CHIMICI DELLE TECNOLOGIE|
|Corso di studi||INGEGNERIA INDUSTRIALE E DEL TERRITORIO|
|Data inizio appello||2018-03-23|
|Disponibilità||Accessibile via web (tutti i file della tesi sono accessibili)|
Lo scopo di questo lavoro è quello di sviluppare differenti trattamenti chimici per: i) recuperare scarti di vetro per i quali la discarica è ancora la prima via di smaltimento; ii) valorizzare scarti di vetro in applicazioni a più alto valore rispetto a quelle in cui sono attualmente utilizzati.
The purpose of the present work is to develop different chemical treatments in order to: i) recovery glass waste for which the landfill is still the first disposal route; ii) valorize glass waste in higher-value applications with respect to those in which they are currently exploited. The glass waste considered are the follow, coming from different streams: - Post-consumer: glass from cathode ray tube (CRT); glass from fluorescent lamps; lead-polluted glass residue from urban collection. - Pre-consumer: borosilicate glass from cosmetic vials. - End of Waste (secondary raw material): glassy sand (coming from the residual part of primary treatment of urban collection glass). In order to have a comparison with the glassy matrix, a different kind of waste, also containing high amount of amorphous silica, was chosen in the work, rice husk ash (RHA) coming from the combustion of rice husk (RH), a food by-product employed as biomass for green energy production. CRT glass and lead-polluted glass residue from urban separated collection were used either as supplementary cementitious material (SCM) or as fine aggregate substitute in cement mortars. In particular, the effect of a mild, sustainable pretreatment based on nitrilotriacetic acid (NTA) was investigated. The depth of penetration and the effect on glass solubility were determined. Results showed that NTA treatment makes the glass less soluble because of lead depletion that should reduce the risk of pollution from leaching. Consequently, the glass behavior in mortars changes: even if the NTA treatment decreases the pozzolanic activity of the glass, making it a filler material rather than SCM, the same treatment allows its use as fine aggregate in substitution of natural sand suppressing ASR reactions. This application is environmentally preferred since it reduces the energetic costs avoiding strong milling process necessary for SCM. Both waste glasses were exploited also as solid support for the adsorption of a lipase (enzyme) obtained from solid-state fermentation of agro-food waste. The resultant biocatalyst is made only from recycled materials. The activity of the immobilized lipase was firstly tested by spectrophotometric method using a typical lipase catalyzed reaction in organic solvent. Results showed that the lipase adsorption was successful on both glasses employed as supports, with catalytic activities ranging between 11-15% (the commercial enzyme/glass system is between 7-14%). After that, the biocatalyst was tested for biodiesel production through the transesterification of waste vegetable oils. Results confirmed the feasibility of the process: methyl esters typical of biodiesel were detected in all the samples containing lipase adsorbed on packaging glass for urban collection, while CRT glass gave a worse performance (probably due to the high Pb content). Glass from fluorescent lamps, borosilicate glass from cosmetic vials, glassy sand and RHA were used as amorphous silica precursors to obtain sodium silicate solutions by means of a mild alkaline treatment. The following parameters were studied for optimization: NaOH concentration; contact time; temperature; solid/liquid weigh ratio; solid particle size; stirring effect. The solutions obtained after filtration were characterized using volumetric titrations based on ISO 1692:1976 and ISO 2124:1972, for the determination of alkali (expressed as Na2O) and silica (SiO2). Compared to waste glasses, RHA was found more reactive towards NaOH solution. In particular, [NaOH]=1.5-2M and contact time=3h are the better conditions to obtain deflocculating agents for ceramics, while [NaOH]=1-1.5M and contact time= 3h are the better conditions to obtain activating solutions for geopolymerization.