Chromium (VI) Adsorption on Activated Lignin

Abstract

Activated lignin, having a surface area of 1023 m2 g-1, has been prepared from lignin sulfate that was treated by 30% H2O2 and carbonized at 300°C in order to test the chromium (VI) adsorption from aqueous solution. The influence of contact time, pH, initial concentration of adsorbent and adsorbate and temperature on the adsorption capacity was investigated. The maximum removal of Cr(VI) was found to be 92.36% at pH=2 and a contact time of 80 min. Optimal concentration of lignin and Cr(VI) was found to be 3.8 gL-1 and 180mg L-1, respectively. The adsorption kinetics was examined with pseudo-first-order and pseudo-second-order equations. The analytical data fit well to the pseudo-second-order equation, and the rate of removal of chromium was found to speed up by increasing the temperature. Activation energy for the adsorption process was found to be 18.19 KJ mol-1. The Langmuir-Freundlich adsorption isotherm models were applied to describe the isotherm and its constants for the adsorption of Cr(VI) on lignin. These constants and correlation coefficients of the isotherm models were calculated and compared with each other. Results indicated that Cr(VI) uptake could be described by the Langmuir adsorption isotherm. The maximum adsorption capacity (qmax) of Cr(VI) on lignin was 75.75 mg g-1 at a temperature of 40°C. The dimensionless equilibrium parameter (RL) signified a favorable adsorption of Cr(VI) on lignin and was found to be between 0.0601 and 0.818 (0L<1). The thermodynamic parameters such as ?G°, ?S°, and ?H° were calculated and it has been found that the reaction was spontaneous and endothermic in nature. This study indicates that lignin has the potential to become an effective and economical adsorbent for the removal of Cr(VI) from waste water.

Synthesis of Nano Calcium Oxide from a Gastropod Shell and the Performance Evaluation for Cr (VI) Removal from Aqua System

“…The Temkin constants (Table ) were obtained from the plot of q e vsln C e . The comparison of the Langmuir parameter, q m (mg/g), obtained from the present studies with the values obtained by other investigators − is presented in Table .…”

Sustainable Lignin-Reinforced Chitosan Membranes for Efficient Cr(VI) Water Remediation

“…When the pH of the solution decreases, H + associates with functional groups such as carboxylic, phenolic, hydroxyl, and carbonyl groups, thus increasing the affinity for Cr(VI) ions because they are positively charged (protonated) [84]. On the other hand, the lower adsorption of Cr(VI) at a high pH is perhaps due to the occurrence of an excess of -OH ions that compete with the negatively charged Cr(VI) ions for the exchange sites on the biosorbent [85]. Such findings are aligned with our results, as higher efficiencies were obtained for samples with lignin and even higher for acidic and neutral pH's.…”

“…It indicates that the protonated amino and hydroxyl groups are sites of electrostatic interaction for the HCrO 4− ion. In other words, chromium is usually introduced as potassium dichromate, which gives a positive charge to the chromium atom in the solution [85]. This results in coordination bonds between the water molecules and the positively charged chromium ions.…”