Effective removal of Cr(VI) ions from aqueous solution using low-cost adsorbents (orange mesocarp, Bengal gram husk, and Khangar): equilibrium, kinetic, and thermodynamic study

Abstract

Several low-cost adsorbents, including orange mesocarp (OMS), Bengal gram husk (BGH), and Khangar, were investigated for their capability to absorb chromium hexavalent ions from synthetic solutions. Process parameters like pH, dose of the adsorbent, concentration of metal ions, and the time they remain in contact were used to calculate the equilibrium adsorption levels. The most crucial factor for removing Cr(VI) ions was observed to be pH. The highest removal for Cr(VI) was determined to be 87%, 90%, and 92%, for OMS, BGH, and Khangar adsorbents respectively. Langmuir adsorption isotherm was observed to be the best fitted, with regression values (R2) of 0.988, 0.974, and 0.989 for OMS, BGH, and Khangar, separately. The kinetic study of Cr(VI) was best expressed with pseudo-second-order. Adsorption process was found to be endothermic and spontaneous in nature with enthalpy (ΔH0) of 48.74, 52.54, and 53.68 KJ mol−1 and entropy of 48.95, 52.78, and 53.93 KJ K−1mol−1 for OMS, BGH, and Khangar respectively. Also, the possible use of OMS, BGH, and Khangar for Cr(VI) ion removal is indicated by the possibility of reusing adsorbents successfully up to three times. According to the study out of the three adsorbents, Khangar was observed to be the most efficient adsorbent for extracting Cr(VI) ions from an aqueous medium.