Lipid humification by soil clays
| dc.contributor.advisor | Clarke, Catherine E. | en_ZA |
| dc.contributor.advisor | Hardie-Pieters, Ailsa G. | en_ZA |
| dc.contributor.author | Adams, Adrian Richard | en_ZA |
| dc.contributor.other | Stellenbosch University. Faculty of Agrisciences. Dept. of Soil Science. | en_ZA |
| dc.date.accessioned | 2019-02-16T14:51:28Z | |
| dc.date.accessioned | 2019-04-17T08:14:36Z | |
| dc.date.available | 2019-02-16T14:51:28Z | |
| dc.date.available | 2019-04-17T08:14:36Z | |
| dc.date.issued | 2019-04 | |
| dc.description | Thesis (PhDAgric)--Stellenbosch University, 2019. | en_ZA |
| dc.description.abstract | ENGLISH ABSTRACT: We studied three aspects of the natural polymerisation (humification) of lipids by soil clays – namely, the products formed, reaction mechanism and kinetics – at environmental temperatures (c. 20–50°C). Various clays were reacted with oleic acid (our chosen model lipid). The Mn-oxide birnessite was the most reactive toward oleic acid, polymerising it into quasi-solid polyesters. A probing of the birnessite-oleic acid reaction mechanism revealed that the formation of a surface exchange complex between oleic acid carboxyl groups and birnessite surface sites (>Mn(III)/>Mn(IV)) is a crucial first step of the reaction. Subsequent chelation and one-electron reduction of Mn(III) to Mn(II) forms radical oleic acid species which couple and thereby polymerise. Kinetic studies revealed that the birnessite-oleic acid reaction was near-linearly dependent on birnessite mass-loading (rate order ~ 0.75) but virtually independent of birnessite surface pH (rate order ~ 0.2). A determined activation energy for the reaction of 12.8 ± 4.2 kJ/mol revealed that it is energetically more spontaneous than the usual autoxidation pathways. These findings broaden our understanding of the role soil clays play in lipid humification in soils. | en_ZA |
| dc.description.abstract | AFRIKAANS OPSOMMING: Ons het drie aspekte van die natuurlike polimerisasie (humifikasie) van lipiede deur grond kleie bestudeer – naamlik, die produkte gevorm, reaksie meganisme en kinetika – teen omgewings-temperature (ong. 20–50°C). Verskeie kleie is met oleïen suur (ons gekose model lipied) gereageer. Die Mn-oksied birnessiet was die mees reaktief teenoor oleïen suur, deur dit te polimeriseer na kwasi-soliede poliësters. 'n Ondersoek na die birnessiet-oleïen suur reaksie meganisme toon dat die formasie van 'n oppervlaks-uitruilingskompleks tussen oleïen suur karboksiel groepe en birnessiet oppervlaks-liggings (>Mn(III)/>Mn(IV)) 'n noodsaaklike eerste stap van die reaksie is. Gevolglike chelasie en een-elektron reduksie van Mn(III) na Mn(II) form radikaal oleïen suur spesies wat koppel en daardeur polimeriseer. Kinetika studies toon dat die birnessiet-oleïen suur reaksie naby-liniêr afhanklik is op birnessiet massa-lading (tempo orde ~ 0.75) maar so te sê onafhanklik is van birnessiet oppervlaks-pH (tempo orde ~ 0.2). 'n Bepaalde aktiverings-energie vir dié reaksie van 12.8 ± 4.2 kJ/mol toon dat dit energiek meer spontaan is as die gewone outoksidasie roetes. Hierdie bevindings verbreed ons begrip van die rol wat grond kleie in lipied humifikasie in gronde speel. | af_ZA |
| dc.description.sponsorship | National Research Foundation (NRF) | en_ZA |
| dc.format.extent | 201 pages : illustrations | en_ZA |
| dc.identifier.uri | http://hdl.handle.net/10019.1/105826 | |
| dc.language.iso | en_ZA | en_ZA |
| dc.publisher | Stellenbosch : Stellenbosch University | en_ZA |
| dc.rights.holder | Stellenbosch University | en_ZA |
| dc.subject | humification, lipids, soil minerals, polyesters, complexation, RGB colour analysis | en_ZA |
| dc.subject | Polymerisation of lipids | en_ZA |
| dc.subject | Humification in soils | en_ZA |
| dc.subject | Soil clays | en_ZA |
| dc.subject | Red, green, blue (RGB) colour analysis | en_ZA |
| dc.subject | UCTD | en_ZA |
| dc.title | Lipid humification by soil clays | en_ZA |
| dc.type | Thesis | en_ZA |