Nitrate sorption on activated carbon modified with CaCl2: Equilibrium, isotherms and kinetics

Abstract

Article Highlights• Activated carbon modified with CaCl 2 is an effective sorbent to remove nitrate from aqueous solutions • Maximum removal was between pH 3 and 9 • The Langmuir, Redlich-Peterson and Sips model isotherms represent the experimental data well with R 2 > 0.99• The sorption kinetics obeyed a second order kinetic model Abstract In this study, nitrate removal from aqueous solutions was investigated using granular activated carbon (GAC) modified with CaCl 2 . Batch sorption studies were performed as a function of sorbent dose, initial nitrate concentration and pH. Sorption was maximized between pH 3 and 9. Studies on the effect of pH showed that the ion exchange mechanism might be involved in the sorption process. The percentage of nitrate removed increased with increasing sorbent concentration, and the ideal sorbent dose was found to be 20 g·L -1 . Four isotherm models -Langmuir, Freundlich, Redlich-Peterson and Sips -were used to fit the experimental data. The Redlich-Peterson isotherm model explained the sorption process well and showed the best coefficient of determination (0.9979) and Chi-square test statistic (0.0079). Using the Sips isotherm model, the sorption capacity (q e ) was found to be 1.93 mg nitrate per g of sorbent. Kinetic experiments indicated that sorption was a fast process, reaching equilibrium within 120 min. The nitrate sorption kinetic data were successfully fitted to a pseudo-second-order kinetic model. The overall results demonstrated potential applications of modified GAC for nitrate removal from aqueous solutions.

Use of coal beneficiation tailings as solid sorbents in the treatment of nitrate-contaminated real wastewater

“…Many technologies have been used in water treatment, including ion exchange (Khan et al 2018(Khan et al , 2019a, reverse osmosis, reduction, precipitation, and membrane filtrations (Kolangare et al, 2018;Rungrodnimitchai and Kotatha 2019;Sheikh et al 2019;Roudbari and Rezakazemi 2018;Erkan et al 2018). Among various technologies for treatment, adsorption has been explored extensively and presents satisfactory results, especially using adsorbents of mineral origin and/or modified surface (Samatya et al 2006;Xi et al 2010;Bhatnagar and Sillanpää 2011;Zanella et al 2015;Tyagi et al 2018;Madhura et al 2018;Tara and Asiri 2020). Adsorption, compared to other methods, is very attractive mainly in terms of design simplicity, easy operation and economic factors when lowcost sorbents are used.…”

“…Chemical modification is also cited as a potential alternative to improve nitrate removal. Zanella et al (2015) obtained around 70% by treating activated carbon with calcium chloride. As activated carbon is negatively charged, nitrate retention by electrostatic interactions is usually very low.…”