Removal characteristics of reactive black 5 using surfactant-modified activated carbon

Reactive dyes are non-degradable and toxic to environments and human being, and their solutions have some color even after wastewater treatment. To remove toxic dyes, adsorption is common choice. In this study, to improve the adsorption capacity, the effect of cationic surfactant was studied to remove reactive black 5 (RB5) by activated carbon (AC) using cetylpyridinium chloride (CPC). Three different ACs were studied; pure AC, AC in CPC solution and precoated AC by CPC. Regardless of surfactant presence, the sorption kinetics followed pseudo-second-order kinetic model. Equilibrium adsorption capacities were determined by fittings experimental data to three well-known isotherm models; Langmuir, Freundlich and double scheme of Langmuir model. A double scheme of Langmuir model was more proper to explain experimental data than the conventional Langmuir and Freundlich model. Cationic surfactant could enhance sorption capacity of RB5 on activated carbon, and the extent of enhancement is highly dependent on pore size distribution of activated carbon.

The effect of surfactant was investigated in the removal of dyes, RB5, onto AC by adsorption. Cationic surfactant, CPC, could contribute Table 3 Parameters for Freundlich and Langmuir adsorption models Freundlich model A* B** C*** Langmuir model KF (mmol/g) 20–60 mesh 8–20 mesh 4–8 mesh 0.40 0.41 0.34 0.38 0.44 0.42 0.39 0.42 0.39 qmax (mmol/g) 20–60 mesh 8–20 mesh 4–8 mesh n 20–60 mesh 8–20 mesh 4–8 mesh 4.93 4.44 3.62 5.64 2.52 2.45 5.87 4.26 4.03 Ka 20–60 mesh 8–20 mesh 4–8 mesh 0.66 0.82 0.86 r2 20–60 mesh 8–20 mesh 4–8 mesh r2 20–60 mesh 8–20 mesh 4–8 mesh 0.77 0.82 0.86 0.73 0.78 0.75 A* 0.10 0.11 0.095 B** C*** 0.09 0.13 0.11 0.10 0.11 0.10 217.63 82.51 7.69 229.33 25.11 8.07 367.73 109.74 49.51 0.86 0.94 0.91 0.97 0.96 0.95 0.97 0.83 0.97 *Pure AC. **Simultaneous additions of CPC and RB5. ***Precoated AC by CPC. Table 4 Parameters for double site Langmuir adsorption model Double site Langmuir model qmax (mmol/g) 20–60 mesh 8–20 mesh 4–8 mesh A* B** C*** 0.13 0.12 0.10 0.10 0.15 0.13 0.10 0.15 0.12 Ka 20–60 mesh 8–20 mesh 4–8 mesh 403.34 437.45 1765.85 405.35 17.58 62.50 367.73 325.43 167.53 Kb 20–60 mesh 8–20 mesh 4–8 mesh 2.16 15.45 3.68 12.02 7.92 0.49 735.47 326.37 4.40 r2 20–60 mesh 8–20 mesh 4–8 mesh 0.96 0.99 0.99 0.99 0.99 0.98 0.97 0.96 0.99 *Pure AC. **Simultaneous additions of CPC and RB5. ***Precoated AC by CPC.