Carbon materials from waste short hemp fibers as a sorbent for heavy metal ions – Mathematical modeling of sorbent structure and ions transport

• Production of carbon sorbents based on waste hemp fibers for heavy metals removal.
• Good sorption properties influenced by chemical treatment of carbon precursors.
• Mathematical modeling of sorbent structure and adsorption process performances.
• Model parameter averaged tortousity correlates sorbent structure with ion transport.
• Effective diffusion coefficient clarifies the mechanism and the rate of adsorption.

Carbonized hemp fibers obtained by carbonization of origin and chemically modified waste hemp fibers was used as a low-cost sorbent for heavy metals removal. The efficiency of carbonized hemp fiber samples as a sorbent was tested through the adsorption of lead ions as a heavy metal model ion. Although changes in carbon precursor structure, induced by chemical modification, affect the sorption process and sorption capacity of carbonized hemp fibers, all carbonized hemp fibers samples show good adsorption properties toward lead ions. Obtained experimental data was used for development of the mathematical model that describes both the phenomenon of metal ions transport through the porous sorbent matrices, and the structure of carbonized hemp fibers. Effective diffusion coefficient, damping coefficient and the lead ion concentration profile within the carbonized hemp fibers, obtained as results of proposed mathematical model, give the insight in the mechanism and the rate of adsorption process, while average tortuosity connected the sorbent structure and ions transport through the sorbent. A good agreement between model prediction for both structural and ion transport model parameters and the experimental data, indicates that the proposed mathematical model can be successfully used for optimization of heavy metal ions adsorption process by correlating the model parameters to the carbonized hemp fibers performances.