Effect of Different Modification Methods on the Adsorption of Manganese by Biochar from Rice Straw, Coconut Shell, and Bamboo

The adsorption capacity of pristine biochar without modificationis usually low. In this experiment, we comprehensively evaluated theadsorption of Mn(II) by biochar with different modification methodsfrom different biomass. The biochar from rice straw, coconut shell,and bamboo was produced by pyrolysis at 600 & DEG;C under nitrogenand then modified with HNO3, NaOH, and Na2S,respectively. The results showed that the adsorption capacities ofthese modified biochar samples were in the order Biochar-NaOH >Biochar-Na2S > Biochar-HNO3. Among the threemodificationmethods, biochar modified with NaOH is the optimum for the adsorptionof Mn(II). However, the same method of modification has differenteffects on different biomass feedstocks. Rice straw: R-C > R-NaOH-C> R-Na2S-C > R-HNO3-C; coconut shell:C-NaOH-C> C-Na2S-C > C-HNO3-C > C-C; bamboo:B-NaOH-C> B-Na2S-C > B-C > B-HNO3-C. At thepH of 5and 30 & DEG;C, R-C, C-NaOH-C, and B-NaOH-C showed the highest maximumadsorption capacity for Mn(II). Equilibrium data were evaluated byLangmuir, Freundlich, and Temkin isotherm models, and the resultssuggested that the Langmuir model is the most suitable to expoundthe adsorption behavior of Mn(II) on R-C, C-NaOH-C, and B-NaOH-C.Overall, the results from this work suggest that the key for preparingbiochar adsorbents with high capacity is to choose the appropriatebiomass feedstock and modification method.