A mechanism of sorption of heavy metal ions from aqueous solutions by chemically modified cellulose

The effect of chemical modification on sorption properties of cotton cellulose with respect to Cu(II), Ni(II), and Fe(II) ions is studied. Modification was carried out through oxidation of cellulose with formation of dialdehyde cellulose, its further conversion to dialdoxime cellulose, and further to a sorbent with hydroxame acidic groups. The optimum conditions for cellulose modification were determined. The sorption capacitance of the modified sorbent is approximately twice as high as that of native cellulose; herewith, the time of establishment of equilibrium is reduced. The mechanism of chemisorption by modified cellulose is due to the presence of new sorption centers—hydroxame acidic groups—in the sorbent structure, alongside with α-hydroxycarboxyl ones. The former, as opposed to the latter, form colored chelate complexes with heavy metal ions on the sorbent surface. Sorption isotherms are well described by the Langmuir model. The limiting sorption capacitance agrees with the amount of acidic groups of sorbents. This allows attributing such a sorbent to cationites and to interpret the mechanism of metal ion sorption from aqueous media by modified cellulose as ion exchange with the presence of -CHOHCOOH and -CONHOH functional groups.