Removal of Congo red from aqueous solution by two variants of calcium and iron based mixed oxide nano-particle agglomerates

Congo red was removed from aqueous solution using nano-crystalline agglomerates of calcium–iron mixed oxide (CaIMO) and iron–calcium mixed oxide (ICaMO) (CaIMO: 30–25 nm; ICaMO: 22–19 nm). The optimum pH was 8.0 (±0.1). Kinetically, pore diffusion with pseudo-second order equation governs the overall adsorption process. Langmuir and Redlich–Peterson isotherms describe the experimental data. Negative ΔGo (−20.78 to −15.25 kJ mol−1) and negative ΔHo (−26.21 and −105.59 kJ mol−1) indicated spontaneous and exothermic reaction. Adsorbents are 4th cycle regenerated using 0.05 M NaOH. Both CaIMO and ICaMO are competitive materials for CR removal from aqueous solution.