BRINE REMEDIATION USING FLY ASH AND ACCELERATED CARBONATION

摘要

Coal combustion by-products such as brines, fly ash and CO_2 from coal fired power plants have the potential to impact negatively on the environment. Brines are loaded with salts which can contaminate the soil, surface and ground waters. Fly ash on the other hand is made up of toxic elements which can leach out due to rain water percolation while CO_2 is the major green house gas contributing to global warming. It has been shown that brine can react with CO_2 leading to formation of carbonates such as calcite, magnesite, siderite and dolomite. These carbonates have the capacity to encapsulate major elements from brine, sequester CO_2 as well as trapping within their matrices trace elements present in brine leading to cleaner brine effluents. This study aims to evaluate and optimize the factors that influence the brine/fly ash/CO_2 interaction chemistry. The CO_2/ brine reactions in the presence of fly ash can potentially provide a viable route for brine clean-up and beneficial remediation of fly ash.Chemical characterization of brine effluents indicates that they are rich in Cl, SO_4, Na, Ca, K and Mg as well as traces such as Fe, Mn, Cr, V, Ti, P, Si and Al and can therefore be utilized as a source of Ca~(2+), Mg~(2+) and Fe~(2+) for the carbonation reactions. Quantitative XRD results reveal that different size fractions of the fly ash have varying proportions of free lime. This lime fraction can be used to raise the brine pH to alkaline levels, maximizing the carbonation efficiency.