Adsorption Properties and Mechanism of Anionic Congo Red Dyeing Wastewater by Steel Slag

The adsorption of Congo red from solution was conducted by using steel slag as the adsorbent.The effects of initial concentrations of Congo red,slag dosages and its particle sizes on the adsorption process were investigated.Under the tested condition,steel slag was observed to adsorb above 95% Congo red,and the adsorption process was not affected by pH and temperature.The amount of dye adsorbed per unit weight of steel slag increased with increasing initial concentrations of Congo red,while decreased slightly with the increase of slag dosages and particle sizes.Kinetic and isotherm studies showed that the adsorption process followed the pseudo-second-order kinetic model and Freundlich model respectively.Compared to the adsorption of cationic dye onto slag,the adsorption amount of slag followed the sequence of Malachite Green(cationic dye)Congo red(anionic dye)Methylene(cationic dye).Analysis results from Fourier transform infrared spectroscopy(FTIR) and scanning electron microscope(SEM) reveal that the adsorption processes are correlated with the combination ways of dyes onto slag surface,depending on the formation of crystal.