Recovery of iron hydroxides from electro-coagulated sludge for adsorption removals of dye wastewater: Adsorption capacity and adsorbent characteristics

The aims of this research work was to investigate the potentials of raw and calcined iron hydroxides/oxides sludge adsorption for DR28 dye removal. The adsorbent is prepared from electro-coagulated (EC) sludge in industrial wastewater treatment plant, as a Nobel adsorbent for decolorizing direct red 28 dye (DR28). The EC sludge adsorbent were prepared with soaking processes and calcination in a range of temperature. The surface properties of raw and calcined EC sludge adsorbent were examined using Zeta Potential, XRD and FTIR. Basic (effect of solution pH, temperature, initial dye concentration) operation parameters were examined for raw and calcined EC sludge adsorbent. The diffraction patter suggests that the crystalline hematite are produced during calcination and increases its intensity as temperature increases. Langmuir and Freundlich Equation were used to model the adsorption equilibrium; and pseudo first and second order Equation were used to model the adsorption kinetics. The results suggested that the adsorption of DR28 dye is chemisorption, the interaction between the adsorbent surfaces with dye is strong. The Langmuir adsorption capacity of DR28 dye with raw and calcined EC sludge adsorbent was calculated as 1.262 mg/g and 1.252 mg/g respectively with experimental conditions: mixing time=20 min, adsorbent dosage=0.5 grams, initial dye concentration=20 mg/L and solution pH=2 at ambient temperature. The adsorption kinetics model data were consistent with the pseudosecond-order. The removal efficiency of 97% was recorded at pH 2, ambient temperature 20 mg/l concentration and 1 g/100 ml for 1 hour. High direct red 28 dye uptake capability and cost-effectiveness of sludge utilization from textile wastewater treatment plant make it potentially attractive for dye removal.