Adsorptive Removal Of Arsenic Using Coal Ash–Melamine–Formaldehyde Resin Composites

Abstract

Due to their toxicity, persistence, and carcinogenicity, development of arsenic contamination in the water systems has become a major environmental and human health issue in most countries worldwide. One of the best and most widely recognized remediation methods is adsorption which have been established to be economical and efficient to the levels of remediation of arsenic with minimal environmental impact. This is a critical account of the most recent advancement in the synthesis of the cheap and performance adsorbents particularly the waste produced products such as coal ash and the way they can be functionally changed by cross-linking the polymer to better their performance. Waste coal ash is a highly inexpensive byproduct in the industries that has got physicochemical inherent characteristics of adsorbents, but when chemically modified, the efficiency can be significantly enhanced. To this end, the crosslinking of the melamine-formaldehyde resin introduces additional functional groups, surface area and structural stability and thereby, increases the adsorption of the arsenic ions capacity. Arsenic in water systems sources and toxicity are discussed systematically and adsorption mechanism is analyzed further with the discussion of electrostatic interaction, exchange of ligand and surface complexation. Most significant operation parameters such as pH, temperature, and contact time and initial concentration of arsenic are considered as crucial vis-a-vis adsorption performance. Also, the kinetic models (pseudo-first-order and pseudo-second-order) and isotherm models (Langmuir and Freundlich) are discussed to describe the adsorption behaviour and efficiency. Recycling and manufacturing of modified adsorbents and their suitability to a real-life application within actual water systems are also discussed. The melamine-formaldehyde cross-linked coal ash composites when compared with other traditional and sophisticated adsorbents is found to have a potential as a cost-effective alternative that may be adopted in the arsenic remediation. Megascales of use and standings of adsorbent are some of the difficulties which have yet to be overcame although greatly enhanced. This review concludes with the conclusion of the research directions that will follow which include material optimization, hybrid technologies, and sustainable deployment strategies to attain the effective removal of arsenic.