Reactive barriers with fly ash zeolites for in situ groundwater remediation

Abstract

In situ chemically reactive barriers or in situ treatment zones are permeable zones emplaced within the aquifer, which reacts with contaminants as contaminated groundwater flows through the zone. This treatment technology can be applied in funnel and gate systems where the plume is forced by slurry trench walls, diaphragm walls, etc., to focus and to pass through a permeable gate with added sorptive particles. In the study on hand, fly ash zeolites (FAZ) are the main reactive constituent of cement/bentonite slurries for grouted screens or FAZ geotextile casings or geosynthetic FAZ liners. The FAZ component is aimed at improving the retention or at least the retardation properties of the sorptive zone or sorptive geotextile element especially for nonpolar organic molecules, and of course, heavy metals. The engineered zeolites as tectosilicates show different dimensions of their channels and cages forming the crystal lattice. They act as molecular sieves. Fly ash zeolites are transformation products from hydrothermal treatment processes of hard coal fly ash (HCF) by sodium hydroxide (NaOH) solutions. The main constituents of fly ash are aluminosilicate glass, mullite and quartz. The zeolite synthesis is controlled by temperature, reaction time, solution molarity, SiO 2/Al 2O 3 ratios and eventual pressure as variable parameters. Fly ashes from different combustion processes and coal of different geological origin treated by different hydrothermal procedures finally end up in different zeolite phases. The process of hydraulic flow through the reactive zone or wall can be enforced by applying electrokinetics to move the contaminants in the soil pore water into treatment zones where the contaminants can be captured or decomposed. The major feature of the technology proposed in this study is the electrodes energized by a direct current which causes water and soluble contaminants to move into or through the treatment zone, and the treatment zones containing reagents that decompose or adsorb the soluble organic contaminants or adsorb contaminants for immobilization or subsequent removal or disposal.