Comparative studies on the removal of chromium(VI) from aqueous solutions using raw and modified Citrus Limettioides peel

Abstract

Citrus Limettioides peel (CLPC) has been modified with sulphuric acid to increase the quantity of sulphonic acid groups improving its metal adsorption capacity. The effect of various parameters such as solution pH, contact time, adsorbent dose and presence of other cations and anions under ambient conditions along with raw citrus limettioides peel (CLP) has been studied. According to the experimental results, the optimal equilibrium time and pH for Cr(VI) ions are found to be 3 h and 2.0 for CLPC and CLP, respectively. The equilibrium data agree well with Langmuir model, which confirm the monolayer coverage of Cr(VI) ions onto CLPC and CLP. The Langmuir monolayer adsorption capacity of the CLPC is found to be 176.50 mg/g which is significantly about 1.8 times greater than that of CLP (99.50 mg/g) at 300 K. The thermodynamic analysis reveals that the adsorption process was spontaneous and exothermic in nature. The kinetic data follow pseudo-second order model with film diffusion process. A single-state batch adsorber has been designed to estimate the amount of adsorbent required to treat the known volume of the effluent using the Langmuir adsorption isotherm. Regeneration study show that CLPC could be effectively utilized for the removal of Cr(VI) ions for seven cycles of operation under study when compared with CLP.