Development of Adsorption Media by Using Industrial Waste: Red Mud for the Removal of As (V) Ions from Water

Abstract

In this study cow dung identified as a neutralizing agent for red mud (RM). Present research estimated a significant reduction in pH value of red mud (10 g) from 10.28 to 8.15 and reduction in alkalinity of ~148 mg/L from ~488 mg/L by adding 80g of cow dung in forty days of anaerobic condition. Titration method, SEM-EDX, FT-IR and XRD applied for characterizing neutralized red mud (NRM). XRD results exhibits a high intensity of quarts and found new compound, the calcium carbide. The acid neutralizing capacity (ANC) of NRM reduce to ~0.87 from~1.506 mol H+/Kg. Based on the resultant research, present study propose cow dung as an efficient neutralizing agent for reducing the pH and alkalinity in the red mud.

Further this neutralized red mud was thermally activated called activated neutralized red mud (ANRM) and another novel adsorbent called red mud modified by lanthanum (La-ARM); prepared by red mud and rare earth element lanthanum was used as a low cost adsorbent for the removal of As (V) from aqueous solution. In the present work a laboratory study was conducted to know the removal efficiency of ANRM and La-ARM for the removal of As (V) from the aqueous solutions by batch method. The experiment was conducted as a function of adsorbent dose, pH, contact time, temperature, initial As (V) concentration, kinetics, thermodynamic and isotherms. The characterization of ANRM and La-ARM before and after adsorption was studied by help of instrumental technique like XRD, SEM-EDX, FT-IR, TG-DTA and chemical methods. Adsorption study was carried out with the initial concentration of 5 mg/L, 10 mg/L and 20 mg/L of As (V) solution. Adsorption kinetics results showed that both the adsorbent follow the pseudo-second order model. The adsorption data was best fitted to Langmuir isotherm model which suggest the monolayer adsorption pattern. The maximum adsorption capacity for ANRM and La-ARM was found to be 2.16 mg/L and 2.408 mg/L respectively. The thermodynamic study suggests the adsorption was spontaneous and endothermic in nature. The intraparticle diffusion model suggests that intraparticle diffusion is not the sole limiting factor. The regeneration and reusability study was done to know the applicability of the adsorbent material. From the above result both the adsorbent was found as an excellent adsorbent for the removal of As (V) from water. This study demonstrates a method which utilized the industrial waste and converting into a valuable resource.