Mass Transfer and Adsorption Kinetics of Phenolic Compounds onto Activated Carbon Prepared from Rice Husk

Activated carbon from an agriculture by-product (rice husk) was prepared by carbonization at 500°C (50°C/15 min) followed by activation at 850°C for 1 h. The adsorption of phenolic compounds onto this activated carbon was studied using batch adsorber methods. The experimental results showed that the prepared activated carbon removed phenolic compounds effectively from aqueous solution.

Analysis of the contact time data gave an indication of the mechanism. The external mass-transfer constant, k_f, involved in the adsorption process was determined using different initial adsorbate concentrations (C₀) and adsorbent masses (M). The following relationships were obtained: k_f = 0.0023(M)^−0.55 and k_f = 0.0006(C₀)^0.17. A macropore rate parameter for intraparticle diffusion, k_p, was defined and used to correlate the experimental data via the following expression: k_p = 0.183(C₀)^0.48.

A twin-resistance mass-transfer model based on external mass transfer and pore diffusion was applied successfully to the system under investigation. Concentration decay curves were predicted using a single modified mass-transfer coefficient, k_f, and a single effective diffusion coefficient, D_eff, for studies involving variable adsorbent masses and initial adsorbate concentrations.