Dr. Valdes-Morales, Hector

This article presents the adsorption of Methylene Blue (MB) onto diatomite, in order to develop a low-cost treatment technology as a process alternative for dye removal. Diatomite used in this work was taken from the Nador area in the northeast of Morocco. Diatomite is characterised by different physical–chemical methods (X-ray diffraction, nitrogen adsorption-desorption isotherm, scanning electron microscopy and Fourier transform infrared). Results showed that the adsorption of MB onto diatomite mineral is affected by various operating parameters like contact time, initial dye concentration, adsorbent dosage, pH and temperature. Adsorption equilibrium is reached after 1.5 h of contact time. Maximum MB removal is obtained at pH = 12. MB removal rate decreases as pH decreases. Adsorption equilibrium data are fitted to Langmuir, Freundlich, Redlich–Peterson and Toth models. Adsorption data are well described by Langmuir isotherm model indicating that a homogeneous adsorption occurs. A maximum adsorption capacity (or monolayer coverage) of 11 mg g–1 is obtained at 45°C. A value of the enthalpy of adsorption of 12.78 kJ mol–1 is found confirming the endothermic nature of adsorption process, while a Gibb’s free energy change (∆G°) falling in the range −30.8 to −35.34 kJ mol–1 confirms the spontaneity of the process. Adsorption kinetics are fitted to a pseudo-second-order kinetic model. Experimental results indicate that the Moroccan diatomite could be used as a potential adsorbent for the removal of cationic dye molecules, at lower cost.

A great number of pollution problems come as a result of the emission of Volatile Organic Compounds (VOCs) into the environment and their control becomes a serious challenge for the global chemical industry. Adsorption is a widely used technique for the removal of VOCs due to its high efficiency, low cost, and convenient operation. In this study, the feasibility to use a locally available clay, as adsorbent material to control VOCs emissions is evaluated. Natural clay is characterised by different physical-chemical methods and adsorptive interaction features between VOCs and natural clay are identified. Toluene (T), methanol (M) and benzaldehyde (B) are used here as representatives of three different kinds of VOCs. Adsorption isotherms onto natural clay and faujasite-Y type zeolite (Fau Y) are obtained at room temperature. According to Langmuir model data, maximum adsorption capacities (qm) of Fez natural clay and zeolite toward methanol (M), toluene (T) and benzaldehyde (B) at 300 K are 8, 0.89 and 3.1 mmol g–1, and 15, 1.91 and 13.9 mmol g–1 respectively. In addition, the effect of temperature on the adsorption of toluene onto natural clay is evaluated in the range from 300 to 323K. An increase on temperature reduces the adsorption capacity of natural clay toward toluene, indicating that an exothermic physical adsorption process takes place. The enthalpy of adsorption of toluene onto Fez natural clay was found to be –54 kJ mol–1. A preliminary cost analysis shows that natural clay could be used as an alternative low cost adsorbent in the control of VOCs from contaminated gas streams with a cost of US$ 0.02 kg–1 compared to Fau Y zeolite with US$ 10 kg–1.

This study aims to evaluate the technical feasibility of applying a low-cost alternative natural bioadsorbent obtained from the cone of the Moroccan cypress Cupressus sempervirens to remove dyes from contaminated waters. Methylene Blue (MB) and Congo Red (CR) dyes are used to represent basic and acid compounds present in wastewater of textile industries. The cone of this medium-sized coniferous evergreen tree was obtained from the Fez area and was characterised by different physical– chemical methods, including nitrogen adsorption–desorption isotherms, Fourier transform infrared spectroscopy, scanning electron microscopy, Boehm titration method and the pH of the point of zero charge (pHpzc). Additionally, the influence of operating conditions such as contact time, initial dye concentration, binary mixture of dye solutions, bioadsorbent dosages and solution pH were evaluated. Experimental results reveal that the adsorption processes take place very rapidly, reaching equilibrium at 30 and 45 min for MB and CR, respectively. Maximum adsorption capacities result to be pH dependents. Hence, MB adsorption is favoured under basic pH conditions, while CR is favoured at acidic pH. A pseudo-second-order kinetic model provides the best fit of the experimental data of MB and CR adsorption onto the biomaterial. Adsorption isotherm data are well represented by Langmuir, Freundlich and Dubinin–Radushkevich models. Langmuir model gives the best fit with a maximum monolayer sorption capacity of 144 and 25.02 mg g–1 for MB and CR, respectively. Experimental results indicate that the cone of Cupressus sempervirens could be used as a potential, low-cost bioadsorbent for the elimination of dyes from contaminated waters.