Fly ash-based adsorbent for adsorption of heavy metals and dyes from aqueous solution: a review

A critical global issue in the 21st century is water shortage, as well as its pollution with noxious metal ions and organic dyes. To extract these pollutants from wastewater, a variety of traditional methods have been employed but they lack reusability/recyclability, are expensive, environmentally unfriendly, unsafe and the remediation process takes a long time. Therefore, to treat these contaminants, nanotechnology (NT) has recently been granted several leeways in terms of making the desirable nanomaterials (NMs) with high surface-to-volume ratios and special surface functionalities. In particular, fly ash (FA) has stood out as one of the greatest exciting new-found affordable and high efficient materials for water decontamination owing to its high porosity, huge surface area, and exceptional features. Hence, this present review study will attempt to compile data from existing literature on the utilization of FA-based adsorbent for the removal of heavy metals (HMs) and dyes from wastewater. Based on the reviewed publications, Langmuir's isotherm models (LIMs) and Freundlich's isotherm models (FIMs) best described the sorption process thus signalling monolayer and multi-layer sorptions. Pseudo-second-order (PSO) model provided the best appropriate means in elucidating the kinetic process and both exothermic and endothermic processes revealed the nature of the thermodynamic process during sorption. Some recommendations in the form of future prospects on how to advance the capacity of the adsorption and effectiveness of FA on the removal of HMs, dyes and other environmental contaminants using innovative technologies such as the nanofiber technology is also been proposed.