The influence of brine chemistry on the workability, strength development and mineralogy of fly ash pastes
Year: 2011
Type: dissertation
Abstract: The ever-increasing demand for energy due to industrialization and \npopulation growth necessitates the combustion of more coal , which results \nin enormous fly ash production. The scarcity of pot able water as well as \nhigh water consumption during mineral and coal processing leads to \ninevitable saline brine production. Both saline brines and fly ashes pose an environmental threat, where utilization of fly ashes is negligible. The management of industrial brines is a concern for inland industries because oceanic disposal is uneconomical . \nIt is therefore imperative to develop an innovative waste disposal practice . \nConsequently, are search study was initiated to investigate the suitability of \nbrines for mine back filling as fly ash pastes . The objective was to examine \nand understand the influence o f brine chemistry on the paste behaviour with \na specific fly ash. The tests involved varying paste consistency, brine and \nfly ash characteristics . \nA redundant Fine Ash Dam (FAD) was studied to establish what transpires \nover the long- term when brines interact with fly ash. Results showed that a \nFAD possesses distinctive chemical , mineralogical and physical properties \nwhich r each equilibrium within 4 years . The presence of approximately 60% \namorphous content and the intrinsic nature of some properties of weathered ash suggest its viability for utilisation as a pozzo lan . Identified secondary \nphases include ettringite (Ca6 [Al(OH)6 ] 2(SO4 ) 3 . 26H2O), pyrrhotite (Fe7S8 ) , \nanalcime (NaAl S i 2O6 ·H2O), C-S-H gel, magnetite (Fe3O4 ) , Strätlingite \n(Ca2Al2SiO2(OH) 1 0 . 8H2O), Friede l ’s salt (Ca3.Al 2O6.CaCl2. 1 0H2 O ) , \nsillimanite (Al 2 S iO5 ) , periclase (MgO) , calcite (CaCO3 ) , gypsum \n(CaSO4 . 2H2O) and halite (NaCl ) . \nExperimental results demonstrated that both salinity and chemical \ncomposition of brines determine the paste behaviour. Optimum brine \nsalinity exists between 40 - 60 g/lf or both synthetic and industrial brines, \nwhere synergistic advantage of individual constituents is realized in a typical brine. Conversely, acid solutions showed undesired paste behaviour \nhence should be excluded in paste preparation. \nChlorides seemed to accelerate the strength development while the use of sulphate solutions to make paste will necessitate stringent monitoring. In \ncontrast, it was discovered that both physical and chemical properties of fly \nash, not just alkalinity determine its effectiveness in immobilizing prevalent \ninorganic species from brines in the paste. \nThis doctoral thesis has demonstrated that co-disposal of brines with fly ash \nas paste if properly engineered will mitigate environmental pollution .
Author: Jabulani S. Mahlaba
Language: English
Subfield: Civil and Structural Engineering
Field: Engineering
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W2924324217