Adsorption of heavy metals from multi-metal aqueous solution by sunflower plant biomass-based carbons

This study reports the competitive adsorption of Ni(II), Cd(II) and Cr(VI) onto sunflower waste biomass carbons, viz. sunflower head carbon and sunflower stem carbon from multi-metal aqueous solution. The adsorption capacity of the adsorbents was highest in mono-metal system but decreased with increase in the number of co-ions. The adsorption capacity in mono-metal system was 0.32 and 0.45 mM/g for Ni(II), 0.25 and 0.32 mM/g for Cd(II) and 0.20 and 0.28 for Cr(VI) by sunflower head carbon and sunflower stem carbon, respectively, whereas, in a binary system, adsorption capacity of sunflower head carbon for Ni(II) was 0.24 mM/g in 0.5 mM Cd(II) solution which was further reduced to 0.18 mM/g in 2.0 mM Cd(II). The effect of co-cations was more pronounced in tertiary systems. Similar behavior was observed for other systems also. The interactive effect of multi-metal ions in binary and tertiary component systems was antagonistic in nature, i.e., the effect of mixture is less than the sum of individual effect of the constituents or when the effect of individual substances added together is less than the expected in response to multiple substances. Langmuir model best fitted the data for all the systems with r² value >0.95.