Abstract
In this study, a coal fly ash material generated in a Portuguese coal thermal powerplant was tested as a low-cost adsorbent to remove dye molecules. Pre-treatment of the coal fly ash samples was not performed in order to reduce end use cost. Physical and chemical characterization revealed their inert nature and low effects lixiviation in aqueous media. Preliminary adsorption studies include adsorbent quantity, and adsorption kinetics. The adsorption studies focused on Mordant Orange 1 (Mo1) dye, but two other molecules, Rhodamine B (RhB) and Methylene Blue (MeB) were also included for comparison reasons. The adsorption isotherms were tested with different models including Langmuir, Freundlich and modified Langmuir-Freundlich. The effect of temperature, pH and unburn carbon in the adsorption process were also studied. The results show that adsorption capacity of the coal fly ash occurs mainly due to electroestatic interactions between the adsorbent surface and the adsorbate, which depends on the pH of the aqueous media and the surface chemistry of the material, quantified by the point of zero charge, pHpzc. These joint effects are responsible for the higher retention of Mo1 that is about 16 times higher, when compared to the other two molecules tested.
Highlights
In recent decades, the world has faced substantial challenges related to energy production driven mainly by health, environment and sustainability issues.[1,2,3] One of them is the large consumption of coal, which generates substantial quantities of coal fly ashes (CFA), the major solid waste from coal-fired thermal powerplants.[4,5] There are environmental and economic reasons to support the valorization of fly ashes: first, the minimization of disposal costs and landfill occupied areas, contributing to circular economy
The purpose of this study was to explore the potentialities of residue such as coal fly ash, generated in coal-fired thermal powerplants, to be used without further treatment as an effective adsorbent to remove dyes from synthetic industrial wastewaters
Results showed that in non-adjusted pH solutions of Mordant Orange 1 (Mo1) the adsorption is favored since pH < pHPZC leading to a positively charged surface of the coal fly ash with adsorption capacities higher than 100 mg g-1 in all temperature range
Summary
The world has faced substantial challenges related to energy production driven mainly by health, environment and sustainability issues.[1,2,3] One of them is the large consumption of coal, which generates substantial quantities of coal fly ashes (CFA), the major solid waste from coal-fired thermal powerplants.[4,5] There are environmental and economic reasons to support the valorization of fly ashes: first, the minimization of disposal costs and landfill occupied areas, contributing to circular economy. The financial return on sales of fly ashes or products produced from waste.[5,6,7] These and other reasons encourage the scientific community to look for new possible applications for CFA waste, taking advantage of relevant properties of this type of material. The chemical and physical characteristics of CFA are crucial in future applications and are strongly
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