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Methylene blue (MB) is a phenothiazine derivative used in microbiology, surgery, diagnostics and as a sensitizer in the photo-oxidation of organic pollutants. These numerous uses of methylene blue could lead to its accumulation in wastewater, causing harmful effects on the environment and living beings. To combat these harmful effects, numerous wastewater treatment processes, particularly physicochemical, were implemented. Adsorption techniques are particularly used to find new natural, biodegradable and inexpensive adsorbents to treat colored waste from structures such as medical and pharmaceutical laboratories. The aim of the present study was to carry out a relevant bibliographical review of the physico-chemical and thermodynamic parameters that can influence this adsorption of methylene blue on activated carbons of natural origin. The results showed a remarkable elimination of methylene blue. However, parameters such as particle size, adsorbent mass, pH, contact time, initial methylene blue concentration, agitation speed and temperature showed that the adsorption capacity of MB on biosorbents was influenced by these quantities. Similarly, the positive and negative enthalpy values (ΔH°) indicated that adsorption process could be endothermic or exothermic. Other thermodynamic parameters, such as the negative value of Gibbs free energy (ΔG°) and the positive value of entropy (ΔS°), also showed that the adsorption process was feasible and spontaneous.
Baldé et al. (Mon,) studied this question.