Bengal Gram Husk as Efficient and Cost-Effective Adsorbent for ${\mathrm{Pb}}^{2+}$ and Methylene Blue Removal in Single and Binary Systems

The present study reported on the utilization of pulse processing waste [Bengal gram peel powder (BGPP)] for the removal of lead ions (${\mathrm{Pb}}^{2+}$) and methylene blue (MB) from aqueous solution in single and binary systems. The characterization of BGPP before and after adsorption was done by various advanced techniques. Results depicted that, whereas the maximum removal of ${\mathrm{Pb}}^{2+}$ occurred within 60 min ($\sim 99\%$ removal), MB took 12 h to attain equilibrium ($\sim 95\%$ removal) with the optimum dose of $2.0\mathrm{g}/\mathrm{L}$ in a single system. It is interesting to note that, at the same dose of $2.0\mathrm{g}/\mathrm{L}$, the equilibrium time was increased to 12 and 20 h for ${\mathrm{Pb}}^{2+}$ and MB, respectively, when ${\mathrm{Pb}}^{2+}$ and MB are present in a mixture (binary system). The optimum pH for ${\mathrm{Pb}}^{2+}$ and MB was 4.5 and 7.0, respectively. The equilibrium data fit well with the Freundlich model. Maximum adsorption capacity obtained was $55.58\mathrm{mg}/\mathrm{g}$ for ${\mathrm{Pb}}^{2+}$ and $24.70\mathrm{mg}/\mathrm{g}$ for MB. Kinetic data complied with a pseudo-second-order model. The results suggest that Bengal gram waste can be utilized as an ecologically friendly adsorbent and it can be used as an economical way for the removal of ${\mathrm{Pb}}^{2+}$ and MB in single as well as in binary systems.