Quick and enhanced separation of Eosin Yellow dye from aqueous solution by FeCl3 interaction: thermodynamic study and treatment cost analysis

Abstract

ABSTRACT Dyes and their metabolites have noxious and carcinogenicity potential and are known to be hazardous for human beings and other living organisms. The discharge of untreated wastewater comprising wide varieties of synthetic dyes into the water resources is one of the vital environmental problems. Therefore, in this study, the efficacy of the chemical coagulation method was explored using ferric chloride as a coagulant to remove the toxic dye Eosin Yellow (EY) from aqueous solution. The interaction between FeCl3 and EY dye was quick and profound at a solution pH of 2.2, yielding the brownish precipitate with a dye removal efficiency of more than 98%. An extremely high dye removal capacity of 1263 mg/g is reported for 100 mg/L of EY dye concentration at optimum experimental conditions. The possible chemical interaction between FeCl3 and EY dye can be attributed to the formation of polymeric complex, as oxygen atoms of carbonyl, phenolate and carboxylate groups of EY dye molecule interact strongly with Fe3+ ions. The presence of various coexisting anions could reduce the EY dye removal efficiency by 2%–5%; however, the required FeCl3 dose has increased from 64 to 170 mg/L. Thermodynamic studies showed that the interaction of EY dye with FeCl3 was exothermic and spontaneous in nature. The investigation of real industrial wastewater samples has exhibited a 90%–215% increase in the required FeCl3 dose as compared to the control experiment for the initial EY dye concentration from 100 to 750 mg/L. Sludge volume index analysis indicates that FeCl3 generated highly dense sludge with good settling characteristics. X-ray diffraction and field emissionscanning electron microscopy characterisation of the generated sludge indicate the polycrystalline nature with a combination of spherical and irregular shape grains of the sludge. Treatment cost analysis revealed that the cost involved in dye removal is in the range of 0.99–3.60 USD ($)/kg of dye removed.