A preliminary study on the adsorptive removal of Cr(VI) using seaweed, Hydrilla verticillata.

The Cr(VI) adsorption efficiency of the seaweed, Hydrilla verticillata, was studied in batches. The adsorbent was characterized using SEM, BET surface area analyzer, Malvern particle size analyzer, EDAX and FT-IR. Cr(VI) removal efficiency of the adsorbent was studied as a function of different adsorption parameters such as contact time, stirring speed, pH, adsorbent dose, particle size, adsorbate concentration, and temperature. Langmuir, Freundlich, and Temkin adsorption isotherm equations were used in the equilibrium modeling. The adsorption process followed pseudo second-order kinetics and intra-particle diffusion was found to be the rate-controlling step. Experimental data follow Langmuir adsorption isotherm. Thermodynamic parameters such as Gibbs free energy and enthalpy of the adsorption process were evaluated to find out the feasibility of the adsorption process. The negative values of Gibb's free energy and positive enthalpy values show the feasibility and endothermic nature of the process. The significance of different adsorption parameters along with their combined effect on the adsorption process has been established through a full 2(4) factorial design. Among the different adsorption parameters, pH has the most influential effect on the adsorption process followed by adsorbate concentration and combined effects of all the four parameters were tested. The correlation among different adsorption parameters were studied using multi-variate analysis.