The mechanism of d-metal ion sorption from aqueous media and chelating sites structures of modified heterocyclic biopolymers

Sorption of d-metal ions (Cu2+, Fe2+, and Ni2+) from aqueous media using modified heterocyclic biopolymers takes place with the participation of sorption sites, with the following acidic groups: α-hydroxycarboxylic (monobasic, bidentate), hydroxamic (monobasic, bidentate), and aldehyde bisulphite (dibasic) in the form of chelate metal complexes, whose structures were determined through the use of computational quantum chemistry on some modeled compounds. Ion exchange mechanism of the components of hetero-phase system in electroneutral, molecular form reflects the implementation of the general laws of thermodynamics: Gibbs’ phase rule, law of mass action, law of equivalent proportions, and law of conservation of charge at electroneutrality of phases. Sorbents functional groups act as sorption sites whose filling goes in accordance with their amount, denticity, basicity and ability of metal cations to complex formation and solvation. The amount and the nature of acid sorption sites of sorbents permits the comparison of their initial and maximum sorption abilities.

Mechanism of protodesorption-exchange of heavy metal cations for protons in a heterophase system of H2O-H2SO4-MSO4-cellulose sorbent

The influence of pH on the distribution of metal cations [Cd(II), Cu(II), Fe(II), Ni(II), Zn(II)] in a four-component heterophase system (H2O-H2SO4-MSO4-cellulose sorbent) was studied. Protodesorption of metal cations was studied with indicator and constant quantities of [MSO4] salts and constant solvent-sorbent ratio. Linear dependence lgКDМ2+=f(рН) with tgα=1/2 of the КDМ2+ metal ions distribution coefficients from the acidity of the aqueous phase is observed in logarithmic coordinates. Depression of the exponent corresponding to proton involvement in protodesorption from 2 (theory) to 0.5 (experiment) indicates that anions of the aqueous phase are involved in the process of exchange of metal cation for proton on the anionic centers of the sorbent, which corresponds to participation of the salt and acid components of the system in molecular non-dissociated form in an equivalent proportion H2SO4/MSO4=1/1. Different behavior of the salt and acid components in ion exchange of cations for cations and cations for protons is due to the differences in the constraint coefficients of their molecular and ionic forms which must be taken into consideration in equations describing thermodynamics of the interphase exchange.