Batch and continuous studies on the removal of heavy metals using biosynthesised melanin impregnated activated carbon

Abstract

Abstract The adversity associated with the removal of melanin nanoparticles after adsorbing heavy metals led to the development of a system involving activated carbon on which melanin was effectively impregnated. The melanin impregnated activated carbon was handily removed from the aqueous medium by simple filtration. The batch studies performed to scrutinise the optimum conditions for maximum adsorption concluded the contact time needed to attain equilibrium to be 90 min for all metals of study. Maximum adsorption of Cr (VI) was shown at pH 3 while Hg (II), Pb (II) and Cu (II) was adsorbed efficiently at pH 5. Increase in temperature favoured the adsorption process for all metals showing maximum removal at 328 K. Melanin impregnated activated carbon could adsorb 84.59% Hg (II), 86.6% Cr (VI), 91.1% Pb (II) and 93.8% Cu (II) from 5 mg/L heavy metal solution. Dynamic studies were conducted by varying the parameters like flow rate, inlet heavy metal concentration and adsorbent loading. Optimum conditions for a maximum breakthrough was obtained with a flow rate of 0.5 mL/min, heavy metal inlet concentration of 1 mg/L and adsorbent loading of 100 mg. Experimental data modelled in equilibrium isotherms showed the best fitting with the Thomas model when compared with the Adam–Boharts model using determined coefficient and error analysis. Efficient chemical desorption of Hg (II), Pb (II) and Cu (II) was obtained using 3N HCl and Cr (VI) using 1N citric acid.