Kinetics of Cd²⁺ and Cr³⁺ Sorption from Aqueous Solutions Using Mercaptoacetic Acid Modified and Unmodified Oil Palm Fruit Fibre(Elaeis guineensis) Adsorbents

The kinetics of the sorption of Cd²⁺ and Cr³⁺ from aqueous solutions by mercaptoacetic acid modified and unmodified oil palm fruit fibre adsorbents were investigated. The results indicate that sorption equilibrium was reached within 60 min for both metals. Also, the removal efficiency of the three adsorbents was observed to increase for both metals with stronger treatments with mercaptoacetic acid. This may be attributed to the influence of the thiolation of the adsorbents. Furthermore, Cr³⁺ had higher removal percentages than Cd²⁺ for all the adsorbents. The sorption mechanism based on the intraparticle diffusion model shows that Cd²⁺ sorption is better described than Cr³⁺. The intraparticle diffusion rate constants, K_id, for Cd²⁺ are 62.04 min^-1 (untreated), 67.01 min^-1 (treated with 0.5 mol/L mercaptoacetic acid), and 71.43 min^-1 (treated with 1.0 mol/L mercaptocacetic acid) while those for Cr³⁺ are 63.41 min^-1 (untreated), 65.79 min^-1 (0.5 mol/L acid treated), and 66.25 min^-1 (1.0 mol/L acid treated).