Removal of Congo red dye from aqueous media using Litchi seeds powder: Equilibrium, kinetics and thermodynamics

Abstract

The continuous quest for colouring materials has led to an increase in dyes production and use in recent times. Some of the dyes usually find their way into water sources which consequently leads to decrease in the aesthetic beauty of the water resource as well as its use potential. This study examined the potential of an agricultural waste (Litchi seed powder (LSP)) for the sequestration of a hazardous dye (Congo red (CR)) from aqueous media. The influence of several experimental drivers such as pH, sorption time, sorbent dosage, particle size and change in water chemistry were also examined. An optimum pH of 2 was established for best uptake of CR. The sorption process can be explained both by the Langmuir and Freundlich isotherm models. The pseudo second order kinetic model best describes the kinetics of the sorption. Scanning electron microscopy showed a significant change in the surface morphology of the spent sorbent. The sorption process was exothermic in nature (ΔH0=−0.45kJ/mol) and spontaneous (−ΔG0=11.52−12.25kJ/mol). Results from this study showed that LSP can be used as a potential low-cost sorbent for dyes decontamination from aqueous media.