Search

This paper presents an in-depth characterization of a raw industrial sludge (IS-R) and its KOH-activated biochar pyrolyzed at 750 °C (IS-KOH-B) followed by their application to remove a cationic dye from aqueous solution. Materials characterization shows that compared to the IS-R, the IS-KOH-B has improved structural, textural, and surface chemical properties. In particular, the IS-KOH-B's BET surface area and total pore volume are about 78 and 6 times higher than those found for the IS-R, respectively. The activated biochar efficiently retained the cationic dye under wide experimental conditions. Indeed, for an initial dye concentration of 50 mg L−1, removal yields were assessed to be more than 92.5%, 93.5%, and 97.8% for a large pH range (4–10), in the presence of high contents of competing cations (3000 mg L−1 of Ca2+, Mg2+, Na+, and K+), and a low used adsorbent dose (1 g L−1), respectively. The Langmuir's adsorption capacities were 48.5 and 65.9 mg g−1 for of IS-R and IS-KOH-B, respectively, which are higher than those reported for various adsorbents in the literature. The dye removal was found to be monolayer, spontaneous, and endothermic for both the adsorbents. Moreover, this removal process seems to be controlled by chemical reactions for IS-KOH-B whereas by both physico–chemical reactions for IS-R. This study demonstrates that the raw industrial sludge and especially its KOH-activated derived biochar could be considered as promising adsorbents for the removal of dyes from aqueous solutions. [ABSTRACT FROM AUTHOR]

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·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. [ABSTRACT FROM AUTHOR]

Abstract One 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. Graphical abstract Image 1 Highlights • Methylene blue desorption was studied in fixed bed column mode. • Methylene blue desorption was governed by an ion exchange mechanism. • Dye recovery was achieved with a high purity level of more than 92%. • Biomass ability for reuse was confirmed after five successive regeneration cycles. • High efficiency and low energy consumption when degrading MB by anodic oxidation. [ABSTRACT FROM AUTHOR]

Studies on the removal of methylene blue (MB) from aqueous solutions by anodic oxidation (AO) using a boron-doped diamond (BDD) electrode, adsorption onto sawdust, and combined treatment have been undertaken. The results proved that AO presents a high efficiency in removing both color and COD in a wide pH interval. The total mineralization of the dye solution was performed in 6 h, which corresponds to relatively high-energy consumption. On the other hand, high sawdust dosage (12 g·L −1 ) was needed to ensure 98% of color and 81% of COD removal. Combining AO and adsorption onto sawdust constitute a very interesting technology. For instance, AO for 1 h followed by sorption permits a reduction in energy consumption by 80 W·h·g COD −1 , a reduction of more than 24 times the adsorbent dose and an enhancement of color and COD removal, indicating that sawdust is efficient in removing not only the MB initial molecules but also the electrogenerated by-products. [ABSTRACT FROM AUTHOR]

Abstract: The present study aims to investigate the key parameters and mechanisms affecting the removal of phosphorus ions from aqueous solutions onto phosphate mine slimes (PMS) in batch mode. PMS is an abundant waste generated by phosphate mine industry. The results indicate that phosphorus removal increases with increasing initial aqueous phosphorus concentrations, adsorbent dosage and temperature, and decreased with increasing pH values. The adsorption data kinetic modeling, the energy dispersive spectroscopy (EDS) and the Fourier transform infra-red spectroscopy (FTIR) analysis before and after adsorption of phosphorus onto PMS show that the main involved mechanisms are both ion exchange with chlorides and sulphur anions and complexation with some functional groups such as hydroxyl, carboxylic and acid halides groups. Furthermore, the results of the elementary composition analysis of PMS before and after adsorption indicated that the phosphorus content in PMS has increased by about 43% which promote its potential to be used as a fertilizer. In comparison with other natural adsorbents, PMS could be considered as one of the most efficient natural materials for the removal and recovery of phosphorus with the possibility of agronomic reuse as fertilizer. [Copyright &y& Elsevier]

Abstract: The present paper aims to study the effectiveness of an abundant marine waste named Posidonia oceanica (P. oceanica) on ammonium removal from aqueous solutions under different experimental conditions. The results of this study have shown that ammonium biosorption onto P. oceanica fibers increases with initial ammonium concentrations and pH increase. Biosorption isothermal data were well fitted by Langmuir model suggesting a monolayer and uniform adsorption process. The kinetic modeling of the experimental data indicated that they were well described by a pseudo-second-order model predicting a chemisorption process. The scanning electron microscopy (SEM), the energy dispersive spectroscopy (EDS) and the Fourier transform Infra-red spectroscopy (FTIR) analysis before and after biosorption of ammonium onto P. oceanica revealed that the main involved mechanisms are both surface ion exchange with magnesium and calcium cations and surface or intraparticle sharing between ammonium and functional groups, such as O–H, N–H, C=O and C–H stretching, and N–H bending. [Copyright &y& Elsevier]

Abstract: Phosphate mine slimes (PMS), an abundant waste generated from phosphate mines, was used in this study as a cost-effective adsorbent to investigate the phosphate anions removal from synthetic and urban secondary treated wastewater solutions. Dynamic experiments using laboratory reactors were carried out to study the effect of phosphate influent concentration, PMS dosage and feed flow rate on phosphate removal and a kinetic model was used to determine the phosphate mass transfer coefficients. The results show that the phosphate removal increases with influent phosphate concentration and PMS dosage. The feed flow rate has no significant effect. On the other hand, the phosphate removal from wastewater is less efficient than the synthetic solution due to anions competition process. The evaluation of phosphates mass transfer coefficients confirms the presence of anion competition phenomena and the necessity of increasing PMS dosage to provide more adsorption sites. The cost-effective and high adsorptive capability of PMS make them attractive materials for phosphate anions removal and recovery from secondary treated wastewaters with the possibility of agronomic reuse as fertilizer. [ABSTRACT FROM AUTHOR]

The purpose of the present research is to investigate the effect of background electrolytes on the phosphorus (P) sorption by four different natural clay samples (NCS): Jebel Tejera-Esghira (JTE) in Medenine area, Douiret (DR) in Tataouine area, Jebel Aidoudi (JA) and Zemlet El Beida (ZB) in Gabes area. The mineralogical and chemical characterization of the NCS showed that they are essentially composed of illite, kaolinite, smectite, with small fractions of quartz and calcite. The P sorption was investigated in batch mode in the presence of three different background electrolytes (CaCl 2 , NaCl and KCl with 99% of purity) under different experimental conditions of contact times (3 h), initial concentrations (25–150 mg.L−1), ionic strength (0–1 M), temperature (295–325 K) and pH (3–11). Experimental results indicated that P sorption in the presence of electrolytes is a rapid process since about 95% of P was observed within a contact time of 180mn. The highest P adsorption capacity was determined to 7.39 ± 0.65, 7.96 ± 0.82, 8.07 ± 0.55 and 8.83 ± 1.05 mg g1 for JTE, JA, ZB and DR. At equilibrium, the P adsorbed amount by the raw NCS was assessed to 7.75 ± 0.55, 8.34 ± 0.75, 8.8 ± 0.3 and 8.85 ± 0.75 mg g−1 for JTE, JA, ZB and DR. This amount increased by about 0.11, 0.08, 0.05%; 0.14, 0.06, 0.04%; 0.17, 0.1, 0.09 and 0.13, 0.11, 0.01% when adding the CaCl 2 , NaCl and KCl respectively. Moreover, the NCS capacity in removing increased with the increase of the initial P concentrations and the decrease of the liquid medium pH values. Also, P adsorption decreases with the increase of temperature. The P kinetic and isothermal removal experimental data were well fitted with the Pseudo-second order and Langmuir models respectively indicating that P adsorption onto NCS particles is mainly governed by chemical processes and occurs heterogeneously on multi-layers surfaces. • Sorption study on natural clay relevant to Tunisia repository program. • Sorption follows ion exchange at low pH and inner sphere complexation at high pH. • Smectite dominates the sorption behavior of natural clay. • Modeling of sorption data for phosphorus-natural clay–ground water system. • Isotherm data are well reproduced by the model at lower phosphorus ion concentration. [ABSTRACT FROM AUTHOR]

Abstract: Adsorption efficiency of orthophosphate from aqueous solution onto Posidonia oceanica fibers (POF) as a raw, natural and abundant material was investigated and compared with other common natural materials. A series of batch tests were undertaken to assess the effect of the system variables, i.e. initial aqueous orthophosphate concentration, contact time, adsorbent dosage, pH and temperature. Results indicate that orthophosphate uptake increased with increasing initial orthophosphate concentration, temperature and adsorbent dosage and decreased with increasing pH values. The maximum adsorption capacity (Q m) determined from the Langmuir isotherm was calculated to be 7.45mgg−1 for the studied orthophosphates concentration range of 15–100mgL−1, pH 7; adsorbent dosage of 2gL−1 and temperature of 20±2°C. The adsorption data were very well described by the pseudo-second order model predicting a chemisorption process. The energy dispersive spectroscopy (EDS) and FTIR analysis before and after adsorption of orthophosphate onto POF showed that the main involved mechanisms are ligand exchange between orthophosphate and Cl−, SO4 2− and OH− and precipitation with calcium. In comparison with other natural adsorbents, raw POF could be considered as one of the most efficient natural materials for the removal of orthophosphate with the possibility of agronomic reuse. [Copyright &y& Elsevier]

Abstract: The present study aims to develop a new potentially low-cost, sustainable treatment approach to soluble inorganic phosphorus removal from synthetic solutions and secondary wastewater effluents in which a plant waste (Posidonia oceanica fiber: POF) is used for further agronomic benefit. Dynamic flow tests using a continuous stirred tank reactor (CSTR) were carried out to study the effect of initial concentration of phosphorus, amount of adsorbent, feeding flow rate and anions competition. The experimental results showed that the removal efficiency of phosphorus from synthetic solutions is about 80% for 10gL−1 of POF. In addition, the variation of the initial concentration of phosphorus from 8 to 50mgL−1 increased the adsorption capacity from 0.99 to 3.03mgg−1. The use of secondary treated wastewater showed the presence of competition phenomenon between phosphorus and sulphate which could be overcoming with increasing the sorptive surface area and providing more adsorption sites when increasing the adsorbent dosage of POF. Compared with columns studies, this novel CSTR system showed more advantages for the removal of soluble phosphorus as a tertiary treatment of urban secondary effluents with more adsorption efficiency and capacity, in addition to the prospect use of saturated POF with nutriment as fertilizer and compost. [Copyright &y& Elsevier]