Composition and performance of multi-layer liner systems to inhibit contaminant transport in a fly-ash dump
| dc.contributor.advisor | Steyl, G. | |
| dc.contributor.author | Mokhahlane, Lehlohonolo | |
| dc.date.accessioned | 2015-11-25T07:23:00Z | |
| dc.date.available | 2015-11-25T07:23:00Z | |
| dc.date.copyright | 2013-07 | |
| dc.date.issued | 2013-07 | |
| dc.date.submitted | 2013-07 | |
| dc.description.abstract | English: The engineering properties of a South African class F fly ash were studied as a potential base liner for a dry coal ash dump. In order to increase the unconfined compression strength, lime and gypsum were added to the fly ash while also aiding in reducing the hydraulic conductivity. Lime was added in the range of 1 to 10% while the gypsum amounts were varied at 1% and 3% per specimen. The constant head method was used to determine the hydraulic conductivity of compacted specimens in the laboratory. Gypsum was observed to have more influence in reducing the hydraulic conductivity as specimens with 3% gypsum had a more reduced hydraulic conductivity that those with 1%. The variations in lime percentages did not appear to reduce the hydraulic conductivity but rather displayed higher values than fly ash specimens without additives when higher percentages of lime were used. A fly ash admixture of 3% lime and 3% gypsum was found to have the lowest hydraulic conductivity of 2.27 x10-9 m/s after 60 days of percolating with brine water. The unconfined compression strength also appeared to be more influenced by gypsum than lime percentages as specimens with 3% gypsum obtained higher strength values than those with 1% gypsum added. Unreacted lime was observed in specimens with higher percentages of lime added and these specimens also presented lower strength values. The addition of lime and gypsum was observed to have limited the release of some trace elements from fly ash. The secondary mineral ettringite was detected and could have possibly precipitated and captured out these toxic elements. An attempt was also made to increase the plasticity index of fly ash using lignosulphonate and values recommended by the South African legislative guidelines for liner materials were obtained. The plasticity was however not retained with subsequent leaching. Two multi-layer liner systems were loaded under different compaction rates in permeameter cells with fitted inflow and outflow points. The primary liners of both systems were able to contain over 95% of leachate that percolated through a waste layer. Compaction rate was found to affect the liners performance as primary liners with a higher compaction rate had less seepage than primary liner compacted at a lower rate. An addition of lime and gypsum improved the overall engineering properties of fly ash to levels accepted by the South African legislative guidelines for a liner material that is able to line hazardous waste. Even though concentrations of some trace elements in fly ash were reduced by addition of lime and gypsum the level of some of these trace elements remain above the threshold set by South African legislative guidelines and therefore remains a health and environmental concern. | en_ZA |
| dc.description.abstract | Afrikaans: Die ingenieurseienskappe van 'n Suid-Afrikaanse klas F-vliegas is ondersoek as 'n potensiële basis voering vir 'n droë steenkoolas-stortingsterrein. Kalk en gips is by vliegas gevoeg om die kompressiekrag te verhoog, terwyl dit ook bydra tot die vermindering van die hidrouliese geleiding. Kalk is bygevoeg in die reeks van 1 tot 10%, terwyl die gipsgetalle gewissel het tussen 1% en 3% per monster. Die konstante drukmetode is gebruik om die hidrouliese geleiding van gekompakteerde monsters in die laboratorium te bepaal. Gips is waargeneem om 'n groter invloed te hê op die vermindering van die hidrouliese geleiding waar monsters met 3% gips 'n meer verminderde hidrouliese geleiding as dié wat met 1% gehad het. Die variasies in kalkpersentasies het skynbaar nie die hidrouliese geleiding verminder nie, maar het eerder hoër waardes getoon as vliegasmonsters sonder bymiddels wanneer hoër persentasies van kalk gebruik is. Dit is bevind dat 'n vliegasmengsel van 3% kalk en 3% gips die laagste hidrouliese geleiding van 2.27 x 10-9 m/s na 60 dae van perkolering met pekel water gehad het. Dit blyk dat die kompressiedrukkrag ook meer beïnvloed word deur gips- as kalkpersentasies aangesien monsters met 3% gips hoër kragwaardes verkry het as dié met 1% gips bygevoeg. Onopgeloste kalk is waargeneem in monsters met 'n hoër persentasie van kalk en hierdie monsters het ook laer kragsterktewaardes. Dit is waargeneem dat die byvoeging van kalk en gips die vrylating van sommige spoorelemente van vliegas verlaag het. Die sekondêre mineraal ettringiet is waargeneem en kon moontlik die giftige elemente uitgeskakel het. 'n Poging is ook aangewend om die plastisiteitsindeks van vliegas te vermeerder deur die gebruik van lignosulfonaat en waardes aanbeveel deur die Suid-Afrikaanse wetgewende riglyne vir die voeringmateriaal. Die plastisiteit is egter nie met die daaropvolgende uitloging behou nie. Twee multi-laag voeringstelsels is gelaai onder verskillende kompaksietariewe in permumeter-selle met ingeboude en uitvloeipunte. Die primêre voerings van beide stelsels was in staat om meer as 95% van logings wat deur 'n afvallaag geperkoleer is, te bevat. Daar is bevind dat die kompaksiekoers die voerings se prestasie beïnvloed, aangesien die primêre voerings met 'n hoër kompaksiekoers minder sypeling het as primêre voerings wat teen 'n laer koers kompakteer. Oor die algemeen het die toevoeging van kalk en gips die fisiese eienskappe van vliegas verbeter tot vlakke wat volgens die Suid-Afrikaanse wetgewende riglyne aanvaarbaar is vir voeringmateriaal wat in staat is om die deursypeling van gevaarlike afval te inhibeer. Selfs al is konsentrasies van sekere spoorelemente in vliegas verminder deur die byvoeging van kalk en gips, is die vlak van 'n sommige van hierdie spoorelemente steeds bo die grens wat deur die Suid-Afrikaanse wetgewende riglyne daargestel is, en dus bly 'n gesondheids- en die omgewingsbekommernis. | af |
| dc.identifier.uri | http://hdl.handle.net/11660/1894 | |
| dc.language.iso | en | en_ZA |
| dc.publisher | University of the Free State | en_ZA |
| dc.rights.holder | University of the Free State | en_ZA |
| dc.subject | Dissertation (M.Sc. (Geohydrology))--University of the Free State, 2013 | en_ZA |
| dc.subject | Fly ash | en_ZA |
| dc.subject | Acid mine drainage | en_ZA |
| dc.title | Composition and performance of multi-layer liner systems to inhibit contaminant transport in a fly-ash dump | en_ZA |
| dc.type | Dissertation | en_ZA |