Features of Sorption and Proton-Desorption of Heavy Metals (M²⁺) from Aqueous Solutions by Biopolymers

Several features of the sorption and proton-desorption mechanisms of heavy metals (M²⁺) from aqueous solutions of acids and native salts (cellulose, chitosan, keratin) by modified biopolymers with acidic (Cell–COOH), salt (^–OOC–W–NH₃⁺), amine (CS–NH₂), and other sorption sites were examined. Sorption isotherms of metal cations from their aqueous salt solutions (pH < 7) by biopolymers were described well in terms of the Langmuir model. The distributions of Cu²⁺, Fe²⁺, Ni²⁺, Zn²⁺, and Cd²⁺ in the heterophasic system H₂O–H₂SO₄–MSO₄–biopolymer were linear functions of the solution acidity in logarithmic coordinates log $\left({K}_{D{\mathrm{M}}^{2+}}\right)$ vs. pH with tan α ≈ 0.5.

Appendix

(1)

(2)

(3)

(4)

(5)

$$ {\displaystyle \begin{array}{l}2{{\mathrm{Na}}^{+}}_{\mathrm{aq}}+\left\{{\left({\mathrm{XH}}_3\mathrm{N}\sim \right)}_2\mathrm{W}\left[{\left(\sim \mathrm{COO}\right)}_2\mathrm{M}\right]\leftrightarrow {\left({\mathrm{XH}}_3\mathrm{N}\sim \right)}_2\mathrm{W}{\left(\sim \mathrm{COO}"{\mathrm{Na}}^{+}\right)}_2\right\}+{{\mathrm{M}}^{2+}}_{\mathrm{aq}}\\ {}2{{\mathrm{H}}_{\mathrm{aq}}}^{+}+\left\{{\left({\mathrm{XH}}_3\mathrm{N}\sim \right)}_2\mathrm{W}\left[{\left(\sim \mathrm{COO}\right)}_2\mathrm{M}\right]\leftrightarrow {\left({\mathrm{XH}}_3\mathrm{N}\sim \right)}_2\mathrm{W}{\left(\sim \mathrm{COO}\mathrm{H}\right)}_2\right\}+{{\mathrm{M}}^{2+}}_{\mathrm{aq}}\end{array}} $$

(6)