Degradation characterisation of various geo-chemical matrices during leaching
| dc.contributor.advisor | Lorenzen, L. | en_ZA |
| dc.contributor.author | Pienaar, Jacoline | en_ZA |
| dc.contributor.other | Stellenbosch University. Faculty of Engineering. Dept. of Process Engineering. | |
| dc.date.accessioned | 2012-08-27T11:34:22Z | |
| dc.date.available | 2012-08-27T11:34:22Z | |
| dc.date.issued | 1999-12 | |
| dc.description | Thesis (M.Ing.) -- University of Stellenbosch, 1999. | |
| dc.description.abstract | ENGLISH SUMMARY: Immobilisation is currently a well-known and cost-effective method in which solid waste can be treated to render hazardous elements less harmful to the environment, by converting the contaminants into their least soluble, mobile or toxic form. The stabilising interaction between the wastes and the solidifying reagents may be either chemical or mechanical. In the latter case, the elements are encapsulated into a monolithic solid. This would evidently require a material of high structural integrity, able to withstand long-term exposure to water infiltration in disposal sites conditions, while continuing to limit the leaching of contaminants into ground or surface waters. Laboratory scale leaching tests are generally used for testing the stability of such materials. Characterisation of these tests is of major importance in clarifying the leaching phenomena, for valid extrapolations of leaching behaviour in a few years’ time (ageing). The impetus of this study was on characterising the degradation behaviour of immobilised matrices during leaching tests. Two specific waste forms (fly ash and jarosite) were stabilised and additives were added to produce two geo-chemical matrix types: (a) a pozzolanic and (b) a geopolymeric matrix. A 5% acetic acid solution was used during batch leaching tests, where the pH was held constant throughout the tests. Regarding crack patterns, the physical degradation appeared somewhat different for the two matrix types. Larger cracks were found in some pozzolanic samples, and the outer layers (of about 5mm) of some samples, appeared detached from the rest of the blocks after leaching. The geopolymeric matrix exhibited smaller cracks and the layers rather flaked off, compared to the larger layers that cracked off the pozzolanic samples. The main degradation mechanisms emerged to be acid attack and the alkali silica reaction for both matrices. The leaching of the main matrix elements was further considered as an indication of the degradation performance. These elements were primarily Si, AI, Fe, Na and Ca. Typically during leaching tests the behaviour is governed by an initial fast surface reaction, followed by much slower diffusion and a slow mobilising chemical reaction and/or corrosion or structural breakdown of the waste matrix. However, a substantial percentage of the elements that leached into the leaching solution were precipitated. A simple semi-empirical model, that considered the effect of degradation, was used to characterise these typical reactions that govern the leaching behaviour of each element. In both matrix types, Ca and Na (and some of the other minor elements) showed a clear reaction front in the leaching phenomenon (difference in leaching rate from the deeper layers of the samples than from surface samples). This is contradictory to the leaching of Si, Fe, Al and Ti. The leaching behaviour of Ca, Na, Mn, Mg and P were very closely related, while in turn, Si, Fe, Al and Ti showed similar behaviour. These similarities in performance indicate that they might be bound into the matrix structure in the same way. The percentages that were leached out after 600 hours were in the same order of magnitude for both matrices, but Si, AI, Ca, and Fe were slightly more stable in the geopolymeric matrix, while Na and Mg were more stable in the pozzolanic matrix. Overall, the geopolymeric matrix seemed to be more structurally stable at extended leaching times. | |
| dc.description.abstract | AFRIKAANSE OPSOMMING: Immobilisasie is tans 'n welbekende en ekonomies vatbare behandelingsmetode om die besoedelingspotensiaal van soliede afval te verminder. Die skadelike elemente word sodoende omgesit in hulle mees onoplosbare, stabiele en nie-toksiese vorms. Dit kan geskied deur of chemiese-, of meganiese interaksie met die matriksbestandele. In laasgenoemde geval word die toksiese elemente vasgevang in 'n monolitiese vastestof. Dit vereis 'n stewige materiaal wat selfs na langtermyn-blootstelling aan stortingsterreinkondisies, steeds voldoende stremming sal plaas op die loging van toksiese elemente na grond- en oppervlak waters. Laboratorium-skaal toetse, bekend as logingstoetse, word as 'n reel aangewend om die stabiliteit van hierdie geimmobliseerde afval te toets. Vir aanvaarbare ekstrapolasies van toetsdata, om langtermyn gedrag te voorspel, is dit dus van belang om die algemene logingsmeganismes te kan verklaar en dit noodsaak gevolglik die karakterisering van logings toetse. Hierdie stu die het spesifiek gefokus op die degradasie-karakterisering van geochemiese matrikse gedurende loging. Twee spesifieke afvalstowwe; jarosiet en vlieg-as, is gestabiliseer en deur die bymiddels te varieer kon verskillende geo-chemiese matrikstipes berei word. Eksperimente is gedoen op twee van hierdie matrikstipes: (a) matrikse van pozzolaniese- en (b) geopolimeriese aard. Wanneer die aard van die kraakpatrone van die verskillende matrikse vergelyk word, vertoon die pozzolaniese matriks groter krake en die buitenste lae (van omttent Smm) is geneig om los te kraak van die blok gedurende die logingstydperk. Die geopolimeer vertoon egter kleiner krakies en die oppervlak is meer geneig om afte flok as die breer (Smm) lae wat van sommige pozzolaanblokke losgekraak het. Die hoof meganismes van degradasie is oenskynlik die suur-aanval- en alkali-silika-reaksies. As verdere degradasie-karakteriseringsmetode, is die logingsgedrag van die hoofmatrikselemente ook beskou. Hierdie elemente is, hoofsaaklik Si, AI, Fe, Na en Ca. Tydens logingstoetse word die gedragtipies gekenmerk deur 'n vinnige oppervlakreaksie by die aanvang van loging, wat gevolg word deur 'n stadiger diffusiereaksie en dan ook derdens 'n stadige mobiliseringsreaksie of degradasie (die fisiese verweer van die matriks struktuur). Vanuit die toetse was dit duidelik dat 'n substansiele deel van die geloogde elemente nie in die oplossing teenwoordig is na loging nie, maar eerder presipiteer en uitsak na die bodem van die logingsbak. 'n Eenvoudige semi-empiriese model, is gebruik om die bydrae van elk van hierdie logingsmeganismes te beskryf vir die loging van elke element. Die effek van presipitasie op die konsentrasies van die logingsoplossing, word egter ook in ag neem. In beide matrikstipes loog Ca en Na uit met 'n duidelike reaksiefront wat van die oppervlak na die dieper dele van die vastestof-monster beweeg, maar Si, Fe, Al and Ti vertoon nie dieselfde gedrag nie. Verder was dit duidelik dat daar 'n ooreenkoms is in die logingsgedrag van Ca, Na, Mn, Mg and P, terwyl Si, Fe, Al and Ti weer eenders uitgeloog het. Hierdie soortgelyke logingsgedrag wys op moontlike ooreenstemmende maniere van gebondenheid in die matriksstruktuur. Die persentasies wat in beide gevalle na 600 uur uitgeloog is, is in dieselfde grootte-orde vir spesifieke e1emente van albei matrikstipes, maar Si, AI, Ca, and Fe het wei effens meer stabiel vertoon in die geopolimeriese matriks, terwyl Na en Mg meer stabiel in die pozzolaniese materiaal was. In geheel het die geopolymeriese matriks, tot 'n mate, 'n groter stabiliteit as die pozzolaniese matriks na langer logings tye. | |
| dc.description.version | Master | |
| dc.format.extent | 192 pages | |
| dc.identifier.uri | http://hdl.handle.net/10019.1/51191 | |
| dc.language.iso | en_ZA | en_ZA |
| dc.publisher | Stellenbosch : Stellenbosch University | |
| dc.rights.holder | Stellenbosch University | |
| dc.subject | Leaching | en_ZA |
| dc.subject | Matrices | en_ZA |
| dc.subject | Dissertations -- Chemical engineering | en_ZA |
| dc.title | Degradation characterisation of various geo-chemical matrices during leaching | en_ZA |
| dc.type | Thesis | en_ZA |
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