Removal of cobalt (II) ions from aqueous solutions utilizing the pre-treated 2-Hypnea Valentiae algae: Equilibrium, thermodynamic, and dynamic studies

The removal of cobalt (II) ions on both raw and pre-treated 2-Hypnea Valentiae algae biomass in a batch system has been investigated. The sorption capacity of the biomass was a function of solution pH, adsorbent dosage, initial ion concentration, and contact time. The experimental studies at 30 °C demonstrated that for an initial Co⁺² concentration of 0.7 mg L⁻¹, at a pH value of 6 and the sorbent dosage of 2 g L⁻¹, the maximum uptakes of Co⁺² are 10.98 mg g⁻¹ and 16.66 mg g⁻¹ on the raw and the formaldehyde (FA)-treated algae, respectively. The equilibrium data at 25 °C were correlated successfully to the Langmuir and Radke-Prausnitz models with high correlation coefficients of 0.97 and 0.99, respectively, and the Langmuir maximum adsorption capacity is 46.03 mg g⁻¹. Investigation of the experimental data at 25 °C with regard to the dynamic behavior of the system showed that the sorption of Co⁺² onto FA-treated algae followed pseudo-second order kinetics with a correlation coefficient of 0.98. In the binary systems the adsorption capacities decreased almost 50% the Co²⁺-Ni²⁺ but only 2% in the Co²⁺-Zn²⁺ system respectively; confirming the competitive sorption between the heavy metals ions in the binary systems is based on their positions in the electrochemical series. The experimental results illustrated that the adsorption of Co⁺² onto the algae biomass is feasible, spontaneous and exothermic. The successful biomass regeneration in a batch system at three cycles revealed the higher efficiency of the 0.1 M HCl solution compared to 0.1 M CaCl₂ and 0.1 M CH₃COOH as desorbing agents.