Removal of indigo carmine (IC) from aqueous solution by adsorption through abrasive spherical materials made of rice husk ash (RHA)

A spherical material made of rice husk ash (RHA) was developed as alternative to the pumice used in the denim washing process via stone wash. The novelty of this work lies in the fact that besides to have shown abrasive properties, this material was also able to remove the Indigo Carmine (IC) contained in textile wastewater effluents. Hence, the stone wash process and the adsorption of IC can be performed at the same time in the washing machine. Thus, this work shows an experimental study on the removal of IC by using this novel material in order to identify the adsorption parameters involved. The experimental campaign was conducted in a discontinuous system. The adsorbent dose (m), soaking time (t), initial concentration (C_o) and temperature (T) were assessed on the treatment of a synthetic wastewater containing IC. Optimum conditions were found to be 40 g 300 mL⁻¹(m) and 300 min (t), while as lower the C_o, the higher removal of IC (Y), although the adsorption capacity (q) decreases. Likewise, the adsorption process was favorably influenced by an increase in the temperature of the solution. Surface characterization was also conducted before and after adsorption by FT-IR, SEM and EDX. Kinetics, isotherms and thermodynamics studies were carried out to describe the experimental data. This work is in line with new environmentally friendly processes in order to zero effluent discharge and demonstrates the potential application of the RHA for conducting both: the stone wash process and the removal of pollutant dyes from wastewater.