Abstract
The aim of the study was to describe the sorption interactions between potentially toxic metals (Cd, Co, Cu, Pb) and materials from an underground coal gasification (UCG) experimental zone. These interactions seem to be significant in terms of the impact of in situ UCG on the groundwater environment. Sorption parameters were determined for two different sample types: subbituminous coal mined from the coal-bed and then subjected to gasification and coal char from the cavity formed by the UCG process. Laboratory-scale tests were carried out using deionized water and aqueous solutions of metals with increasing concentrations. The Freundlich isotherm model was applied to describe sorption phenomena due to nonlinear mass distribution of adsorbed metal ions as a function of equilibrium concentration and assuming physical interactions only. In addition, the efficiency of the tested sorbents for metal removal was calculated. In the case of subbituminous coal, the percent removal ranged from a minimum of 3.6–9.8% (for cobalt) to a maximum of 43.4–79.8% (for lead). Char removed metals more efficiently (min. 26.6–94.8% for cadmium; max. 98.5–99.9% for lead). Furthermore, the sorbates can be ranked according to the metal ion binding efficiency to sorbents in the following order: Co < Cd < Cu < Pb. The sorption characteristics of materials obtained from the post-UCG cavity may be used to evaluate the retardation parameters of inorganic pollutant migration in the environment around a georeactor.
Highlights
The underground coal gasification (UCG) technology obtains energy in the form of gas generated through the in situ gasification of coal deposits, which is extracted to the surface
In addition to basic organic pollutants such as phenols, benzene derivatives (BTEX), and polycyclic aromatic hydrocarbons (PAHs), the UCG process generates a significant number of inorganic impurities, 1 3 Vol.:(0123456789)
The filtrate physicochemical analysis results obtained after the static sorption tests with subbituminous coal and char are given in Tables 5 and 6
Summary
The underground coal gasification (UCG) technology obtains energy in the form of gas generated through the in situ gasification of coal deposits, which is extracted to the surface. Despite its many economic and environmental advantages, the gasification of coal, like any oxidation process, generates a number of solid, liquid, and gaseous by-products that may contain substances hazardous to the water and soil environment (Bhutto et al 2013; Campbell et al 1979; Dalton and Campbell 1978; Humenick and Mattox 1978; Liu et al 2007; Nakaten et al 2014a, b; Sury et al 2004). In addition to basic organic pollutants such as phenols, benzene derivatives (BTEX), and polycyclic aromatic hydrocarbons (PAHs), the UCG process generates a significant number of inorganic impurities,
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