Abstract. The feasibility of using medicinal plants species Retama raetam as a low cost and an eco-friendly adsorbent for the adsorption of cationic dye methylene blue from simulated aqueous solution has been investigated. Adsorption kinetics of methylene blue onto Retama raetam plants was studied in a batch system. The effects of pH and contact time were examined. The methylene blue maximum adsorption occurred at pH 8 and the lowest adsorption occurred at pH 2. The apparent equilibrium was reached after 120 min. Optimal experimental conditions were determined. Adsorption modelling parameters for Freundlich and Langmuir isotherms were determined and, based on R 2 , various error distribution functions were evaluated as well. Adsorption isotherm was best described by non linear Freundlich isotherm model. Thermodynamic studies show that adsorption was spontaneous and exothermic. For determining the best-fi t-kinetic adsorption model, the experimental data were analyzed by using pseudo-fi rst-order, pseudo-second-order, pseudo-third-order, Esquivel, and Elovich models. Linear regressive and non-linear regressive method was used to obtain the relative parameters. The statistical functions were estimated to fi nd the suitable method that fi t better the experimental data. Both methods were appropriate for obtaining the parameters. The linear pseudo-second-order (type 9 and type 10) models were the best to fi t the equilibrium data. The present work showed that plant Retama raetam can be used as a low cost adsorbent for the removal of methylene blue from water.Keywords: Retama raetam, methylene blue, removal, modelling, adsorption.
IntroductionThe textile industry is one of industrial waste water source. This contaminated water is very toxic for the humans and animals [1]. Methylene blue is used in colouring paper, dyeing cottons, wools, silk, leather and coating for paper stock. Although methylene blue is not strongly hazardous, it can cause some harmful effects, such as heartbeat increase, vomiting, shock, cyanosis, jaundice, quadriplegia, and tissue necrosis in human organisms [2].Chemical coagulation-fl occulation [3], different types of oxidation processes [4], biological process [5], membrane-based separation processes [6] and adsorption [7] were the treatments used in the purifi cation of waters. The most effi cient method used for the quickly removal of dyes from the aqueous solution is the physical adsorption [8]. Biosorbents, such as wood sawdust [9], waste-biomass [10], delonix regia [11], agricultural solid waste [12], are able to remove effi ciently the colour from water.Retama raetam plants can be used as biosorbent. This species belonging to the Fabaceae family has a very productive vertical and horizontal root system, which can reach 20 m. This, in turn, increases substantially the stabilization of the soil. Moreover, the Retama species contributes to the biofertilisation of poor grounds, because of their aptitude to associate with fi xing nitrogen bacteria Rhizobia. Therefore, the genus of Retama is ...
