Optimization of a cationic dye desorption from a loaded-lignocellulosic biomass: factorial design experiments and investigation of mechanisms

The sustainable management of loaded adsorbents with organic pollutants represents an important environmental challenge. The current research work investigates the regeneration process optimization of raw orange tree sawdust (ROS) loaded with methylene blue (MB) by using NaCl solutions as eluent. The MB desorption was assessed in static mode under different process variables, notably the desorbing NaCl solution’s pH and concentration and the MB-loaded biomass dose. A full factorial design composed of 24 experiments was employed to apprehend the statistical significance of each followed parameter. Experimental results showed that the maximum desorption yield was estimated to be about 82.4% for the following parameter’s values: aqueous pH $=$ 3, [NaCl] $=$ 0.2 M and MB-loaded-ROS dosage in the desorbing solution $=$ 1 g$\cdot$L$^{-1}$. The statistical study confirmed the good fit of the experimental data with the statistical model used as well as regression and adjusted regression coefficients of about 99.0% and 96.6%, respectively. Moreover, the ranking of the effect of each studied parameter in terms of standardized effect on the desorption efficiency of MB from ROS was assessed through ANOVA test. The desorption mechanisms involved were explored by using multiple analysis techniques. It appears that the MB molecules’ desorption from ROS’s particles is mainly driven by a counter chemisorption process based on cationic exchange with the sodium and hydronium ions present in the desorbing solutions

Investigations on lignite use for lead removal from aqueous solutions under static and dynamic conditions: adsorption properties and mechanism exploration

Lignite, as an abundant and low-cost material, was tested for lead (Pb(II)) removal from aqueous solutions under various experimental conditions for both static (batch) and dynamic (column) experiments. Static assays showed that Pb(II) removal efficiency increases with rising in its initial concentration, aqueous pH, and adsorbent dosage values. Adsorption kinetic and isothermal data were well fitted with the pseudo-second-order and Freundlich models, respectively, suggesting that lead removal by lignite is mainly governed by chemical processes and occurs heterogeneously on multilayer surfaces. The maximum Langmuir’s adsorption capacity was equal to 61.4 mg$\cdot$g$^{-1}$, which is high in comparison to various natural materials. The laboratory column experiments showed that Pb(II) breakthrough curves and subsequent lignite adsorption efficiency is highly dependent on the bed height. Due to the short time contact between Pb(II) and lignite particles inside the column, the highest adsorption capacity was about 21%, which is lower than the one found in the batch mode. Even under dynamic conditions, lignite exhibits a high adsorption capacity compared to other adsorbents, which promotes its use as a low-cost and efficient material for Pb(II) and the removal of other heavy metals from wastewaters

Optimization of a cationic dye desorption from a loaded-lignocellulosic biomass: factorial design experiments and investigation of mechanisms

The sustainable management of loaded adsorbents with organic pollutants represents an important environmental challenge. The current research work investigates the regeneration process optimization of raw orange tree sawdust (ROS) loaded with methylene blue (MB) by using NaCl solutions as eluent. The MB desorption was assessed in static mode under different process variables, notably the desorbing NaCl solution’s pH and concentration and the MB-loaded biomass dose. A full factorial design composed of 24 experiments was employed to apprehend the statistical significance of each followed parameter. Experimental results showed that the maximum desorption yield was estimated to be about 82.4% for the following parameter’s values: aqueous pH $=$ 3, [NaCl] $=$ 0.2 M and MB-loaded-ROS dosage in the desorbing solution $=$ 1 g$\cdot$L$^{-1}$. The statistical study confirmed the good fit of the experimental data with the statistical model used as well as regression and adjusted regression coefficients of about 99.0% and 96.6%, respectively. Moreover, the ranking of the effect of each studied parameter in terms of standardized effect on the desorption efficiency of MB from ROS was assessed through ANOVA test. The desorption mechanisms involved were explored by using multiple analysis techniques. It appears that the MB molecules’ desorption from ROS’s particles is mainly driven by a counter chemisorption process based on cationic exchange with the sodium and hydronium ions present in the desorbing solutions

Investigations on lignite use for lead removal from aqueous solutions under static and dynamic conditions: adsorption properties and mechanism exploration

Lignite, as an abundant and low-cost material, was tested for lead (Pb(II)) removal from aqueous solutions under various experimental conditions for both static (batch) and dynamic (column) experiments. Static assays showed that Pb(II) removal efficiency increases with rising in its initial concentration, aqueous pH, and adsorbent dosage values. Adsorption kinetic and isothermal data were well fitted with the pseudo-second-order and Freundlich models, respectively, suggesting that lead removal by lignite is mainly governed by chemical processes and occurs heterogeneously on multilayer surfaces. The maximum Langmuir’s adsorption capacity was equal to 61.4 mg$\cdot$g$^{-1}$, which is high in comparison to various natural materials. The laboratory column experiments showed that Pb(II) breakthrough curves and subsequent lignite adsorption efficiency is highly dependent on the bed height. Due to the short time contact between Pb(II) and lignite particles inside the column, the highest adsorption capacity was about 21%, which is lower than the one found in the batch mode. Even under dynamic conditions, lignite exhibits a high adsorption capacity compared to other adsorbents, which promotes its use as a low-cost and efficient material for Pb(II) and the removal of other heavy metals from wastewaters

Optimization of a cationic dye removal by a chemically modified agriculture by-product using response surface methodology: biomasses characterization and adsorption properties

International audienceThe present study investigates the alkaline modification of raw orange tree sawdust (ROS) for an optimal removal of methylene blue (MB), as a cationic dye model, from synthetic solutions. The effects of operating parameters, namely, sodium hydroxide (NaOH) concentrations, ROS doses in NaOH solutions, stirring times, and initial MB concentrations on dye removal efficiency, were followed in batch mode. The process optimization was performed through the response surface methodology approach (RSM) by using Minitab17 software. The results showed that the order of importance of the followed parameters was NaOH treatment concentrations > stirring times > initial MB concentrations > ROS doses in NaOH solutions. The optimal experimental conditions ensuring the maximal MB removal efficiency was found for a NaOH treatment concentration of 0.14 M, a stirring time of 1 h, a ROS dose in NaOH solutions of 50 g L(-1), and an initial MB concentration of 69.5 mg L(-1). Specific analyses of the raw and alkali-treated biomasses, e.g., SEM/EDS and XRD analyses, demonstrated an important modification of the crystalline structure of the wooden material and a significant increase in its surface basic functional groups. Kinetic and isotherm studies of MB removal from synthetic solutions by ROS and the alkali-treated material (ATOS) showed that for both adsorbents, the pseudo-second-order and Langmuir model fitted the best the experimental data, respectively, which indicates that MB removal might be mainly a chemical and a monolayer process. Furthermore, thanks to the chemical modification of the ROS, the MB maximal uptake capacity has increased from about 39.7 to 78.7 mg g(-1). On the other hand, due to the competition phenomenon, the coexistence of MB and Zn(II) ions could significantly decrease the MB removal efficiency. A maximal decrease of about 32 % was registered for an initial Zn(II) concentration of 140 mg L(-1). Desorption experiments undertaken at natural pH (without adjustment: pH = 6) and with different NaCl concentrations emphasized that the adsorbed MB could be significantly desorbed from both the tested materials, offering their possible reuse as efficient adsorbents. All these results confirmed that NaOH-treated orange tree sawdust could be considered as an efficient, economic, and ecological alternative for the removal of cationic dyes from industrial wastewaters

Dynamic investigations on cationic dye desorption from chemically modified lignocellulosic material using a low-cost eluent Dye recovery and anodic oxidation efficiencies of the desorbed solutions

International audienceOne of the main challenges of dyes adsorption technology application wide-spreading is the fate of the generated dyes-loaded-biomasses, which in certain cases could represent a serious threat to the environment. In this research work, an innovative and eco-friendly approach was established for the management of a lignocellulosic material (alkaline treated orange tree sawdust ATOS) loaded with methylene blue (MB) at a concentration of 107 mg g(-1). This approach consists first of all to a rapid and important MB desorption (more than 91%) from fixed bed depth columns by low cost saline solutions (NaCl 0.5 M). The issued solutions contained high MB concentrations (>3400 mg L-1) permitting a partial recovery of the dye as a solid phase with a purity of 93% that could be reused again in the industrial process. The second step concerns the treatment of the remaining dissolved MB in the desorbed solutions through anodic oxidation process by using bipolar Si/BDD (Boron Doped Diamond) electrodes. The presence of chlorides anions in the desorbed solutions enhances considerably their discoloration and organic carbon removal efficiencies and kinetics and significantly reduces the related consumed energy. The quality of the resulting treated wastewaters allows its possible reuse in the industrial process. Finally, five consecutive adsorption/desorption cycles experiments showed that ATOS could be reused several times for the MB adsorption without significant efficiencies decrease. All these results confirm the validity of our strategy aiming to turn dyes-loaded-lignocellulosic-biomasses from pollution source to values. (C) 2018 Elsevier Ltd. All rights reserved

Use of Lignite as a Low-Cost Material for Cadmium and Copper Removal from Aqueous Solutions: Assessment of Adsorption Characteristics and Exploration of Involved Mechanisms

Lignite, as an available and low-cost material, was tested for cadmium (Cd) and copper (Cu) removal from aqueous solutions under various static experimental conditions. Experimental results showed that the removal efficiency of both metals was improved by increasing their initial concentrations, adsorbent dosage and aqueous pH values. The adsorption kinetic was very rapid for Cd since about 78% of the totally adsorbed amounts were removed after a contact time of only 1 min. For Cd and Cu, the kinetic and isothermal data were well fitted with pseudo-second order and Freundlich models, respectively, which suggests that Cd/Cu removal by lignite occurs heterogeneously on multilayers surfaces. The maximum Langmuir’s adsorption capacities of Cd and Cu were assessed to 38.0 and 21.4 mg g−1 and are relatively important compared to some other lignites and raw natural materials. Results of proximate, scanning electron microscopy/energy dispersive X-ray spectroscopy (SEM/EDS), Fourier transform infrared spectroscopy (FTIR) and X-Ray diffraction (XRD) showed that the removal of these metals occurs most likely through a combination of cation exchange and complexation with specific functional groups. The relatively high adsorption capacity of the used lignite promotes its future use as a low cost material for Cd and Cu removal from effluents, and possibly for other heavy metals or groups of pollutants