Agricultural biomass/waste as adsorbents for toxic metal decontamination of aqueous solutions

Toxic metals can be present in the environment, causing negative effects on the ecosystem and human health. Although several technologies have been used for decontamination purposes, biosorption is an environmentally friendly and cost-effective alternative to remove toxic metals from wastewater. Agricultural biomasses are a class of biosorbents that offer several advantages, including their low cost, availability in nature, simplicity to be obtained and used as adsorbents. This review article is focused on the use of agricultural biomass materials for the removal of toxic metal(oid)s from contaminated aqueous matrices. In addition, raw and modified forms of these biosorbents are considered as precursors for the preparation of other adsorbents like biochar. Following agricultural biomasses are discussed: i) watermelon, ii) potato, iii) cucumber, iv) peanut, v) almond, vi) walnut and hazelnut, vii) pistachio, and viii) tea waste-based biosorbents. The adsorption potential of the biomasses is exhibited under the optimum experimental conditions, and their characterization and possibility to reuse is also considered. Moreover, isotherm and equilibrium parameters of the metal(oid) adsorption by the biomasses are discussed. Specifically, thermodynamic studies are described in order to better understand the nature of the biosorption process between contaminant and biomass. All these considerations reflect the high potential of agricultural waste-based adsorbents for toxic metal(oid)s removal related to wastewater treatment technologies.Fil: Anastopoulos, Ioannis. University Of Cyprus; ChipreFil: Pashalidis, Ioannis. University Of Cyprus; ChipreFil: Hosseini Bandegharaei, Ahmad. Sabzevar University Of Medical Sciences; Irán. Islamic Azad University; IránFil: Giannakoudakis, Dimitrios A.. Polish Academy of Sciences; PoloniaFil: Robalds, Artis. Animal Health And Environment Bior; LetoniaFil: Usman, Muhammad. University Of Agriculture; PakistánFil: Escudero, Leticia Belén. Universidad Nacional de Cuyo. Facultad de Ciencias Exactas y Naturales. Laboratorio de Química Analítica para Investigación y Desarrollo; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza; ArgentinaFil: Zhou, Yaoyu. Hunan Agricultural University; ChinaFil: Colmenares, Juan Carlos. Polish Academy of Sciences; PoloniaFil: Núñez Delgado, Avelino. Universidad de Santiago de Compostela; EspañaFil: Lima, Éder Claudio. Universidade Federal do Rio Grande do Sul; Brasi

Investigations on the Interaction of EDTA with Calcium Silicate Hydrate and Its Impact on the U(VI) Sorption

The interaction of EDTA with calcium silicate hydrate (C-S-H) and its impact on the sorption of U(VI) by C-S-H in the presence of EDTA at varying concentrations has been investigated under N2 and ambient atmosphere. The solid phase characterization was performed by FTIR, XRD and TGA measurements and the uranium concentration in solution has been determined by alpha-spectroscopy. At increased EDTA concentrations ([EDTA] > 0.1 M) calcium is complexed and extensively extracted from the solid resulting in a quantitative dissolution of the Ca(OH)2 phase and deterioration of C-S-H. At lower EDTA concentrations ([EDTA] ≤ 0.01 M), EDTA is sorbed into the solid phase and the associated adsorption capacity (qmax = 0.67 mol/kg) has been evaluated by fitting the corresponding data with the Langmuir isotherm model. The incorporation of EDTA in the C-S-H matrix was corroborated by FTIR, XRD and TGA measurements. Regarding the effect of EDTA on the U(VI) sorption by C-S-H, evaluation of the experimental data reveal a significant decrease of the Kd values in the presence of EDTA most probably due to the stabilization of U(VI) in the form of U(VI)-EDTA complexes in solution. Under ambient conditions a further decrease of the Kd values is observed because of the formation of U(VI)-carbonato complexes related to CO2 dissolution and hydrolysis

Studies on parameters affecting uranium leaching from phosphate rock

The effect of various chemical parameters such as NO3-, HCO3-, EDTA and citric acid on the uranium leaching from phosphate rock samples has been investigated by means of batch-type experiments and the total uranium concentration in the solution was analyzed by ICP-OES. EDTA has been found to leach uranium from phosphate rock at the highest rate, followed by carbonate and citrate. With the exception of nitrates, the ligand concentration (0.01 M and 0.001 M) appears to greatly enhance the leaching efficiency at the studied ligand concentrations. On other hand, the effect of pH differs significantly from one ligand to another, because EDTA is more effective in near neutral solutions (pH 6.5), whereas citrate in acidic solutions (pH 2.5)

Actinide Ion (Americium-241 and Uranium-232) Interaction with Hybrid Silica–Hyperbranched Poly(ethylene imine) Nanoparticles and Xerogels

The binding of actinide ions (Am(III) and U(VI)) in aqueous solutions by hybrid silica–hyperbranched poly(ethylene imine) nanoparticles (NPs) and xerogels (XGs) has been studied by means of batch experiments at different pH values (4, 7, and 9) under ambient atmospheric conditions. Both materials present relatively high removal efficiency at pH 4 and pH 7 (>70%) for Am(III) and U(VI). The lower removal efficiency for the nanoparticles is basically associated with the compact structure of the nanoparticles and the lower permeability and access to active amine groups compared to xerogels, and the negative charge of the radionuclide species is formed under alkaline conditions (e.g., UO2(CO3)34− and Am(CO3)2−). Generally, the adsorption process is relatively slow due to the very low radionuclide concentrations used in the study and is basically governed by the actinide diffusion from the aqueous phase to the solid surface. On the other hand, adsorption is favored with increasing temperature, assuming that the reaction is endothermic and entropy-driven, which is associated with increasing randomness at the solid–liquid interphase upon actinide adsorption. To the best of our knowledge, this is the first study on hybrid silica–hyperbranched poly(ethylene imine) nanoparticle and xerogel materials used as adsorbents for americium and uranium at ultra-trace levels. Compared to other adsorbent materials used for binding americium and uranium ions, both materials show far higher binding efficiency. Xerogels could remove both actinides even from seawater by almost 90%, whereas nanoparticles could remove uranium by 80% and americium by 70%. The above, along with their simple derivatization to increase the selectivity towards a specific radionuclide and their easy processing to be included in separation technologies, could make these materials attractive candidates for the treatment of radionuclide/actinide-contaminated water

Americium Sorption by Microplastics in Aqueous Solutions

The interaction of americium by polyamide (PN6) and polyethylene (PE) microplastics (MPs) has been investigated in de-ionized and seawater samples traced with the Am-241 isotope. The effect of the pH and composition of the aqueous solution (seawater) on the sorption efficiency (Kd) have been studied as function of time. In addition, the americium sorption using radionuclide mixtures (e.g., Am-241 and U-232) and its desorption in the presence of EDTA was investigated by means of bath-type experiments. The experimental data (e.g., Kd values) revealed that the sorption efficiency depends on the MP type and the pH that governs the Am(III) speciation in the solution, and the PN6 surface charge determines the sorption efficiency. Moreover, the desorption of Am(III) from MPs is a time-depended process, and the presence of complexing agents (e.g., EDTA) enhances the desorption efficiency. The Kd values in the studied water samples were relatively close to one another and similar to corresponding values in soil systems, indicating the significant role of microplastics on the behavior of americium in natural aquatic systems

The Effect of Humic Acid on the Formation and Solubility of Secondary Solid Phases of Polyvalent Metal Ions

The paper presents and discusses experimental data regarding the effect of natural organic matter (e.g. humic acid) on the formation and solubility of secondary solid phases of polyvalent metal ions (e.g. M(VI), M(IV), M(III)) in aqueous solutions of 0.1 M NaClO4 and under normal atmospheric conditions. The experimental work has been carried out using hexavalent uranium as analogue for M(VI), tetravalent thorium, cerium and zirconium as analogues for M(IV) and trivalent samarium and neodymium as analogues for M(III). The solid phases under investigation have been prepared by alkaline precipitation in the presence and absence of humic acid and characterized by TGA, ATR-FTIR, XRD and solubility measurements. The experimental data obtained indicate generally that the solid phases, which are formed in the absence of humic acid, are stable and remain the solubility limiting solid phases even in the presence of increased humic acid concentration (up to 0.5 g l-1) in solution. Although polyvalent metal ions form very stable complex with humic acid, upon base addition in the M(z)-humic acid system decomplexation of the previously formed M(z)-humate complexes and precipitation of two distinct phases occurs, namely, the inorganic and the organic phase. The latter is adsorbed on the particle surface of the former. However, natural organic matter (humic acid) affects the particle size of the solid phases and may lead to reduction of redox-sensitive species. Generally, increasing humic acid concentration results in decreasing crystallite size of the inorganic solid phase. The extent of the effect depends inversely on the solid phase stability

Copper Adsorption by Magnetized Pine-Needle Biochar

The Cu(II) adsorption from aqueous solutions by magnetic biochar obtained from pine needles has been studied by means of batch-type experiments. The biochar fibers have been magnetized prior (pncm: carbonized-magnetized pine needles) and after oxidation (pncom: carbonized-oxidized-magnetized pine needles) and have been used as adsorbents to study the presence of carboxylic moieties on the magnetization and following adsorption process. The effect of pH (2–10), initial metal concentration (10−5–9·10−3 mol·L−1) and contact time (0–60 min) has been studied by varying the respective parameter, and the adsorbents have been characterized by Fourier transform infrared (FTIR) and X-ray diffraction (XRD) measurements prior and after Cu(II)-adsorption. FTIR measurements were performed to investigate the formation of surface species and XRD measurements to record possible solid phase formation and characterize formed solids, including the evaluation of their average crystal size. The data obtained from the batch-type studies show that the oxidized magnetic biochar (pncom) presents significantly higher adsorption capacity (1.0 mmol g−1) compared to pncm (0.4 mmol g−1), which is ascribed to the synergistic effect of the carboxylic moieties present on the pncom surface, and the adsorption process follows the pseudo-second order kinetics. On the other hand, the FTIR spectra prove the formation of inner-sphere complexes and XRD diffractograms indicate Cu(II) solid phase formation at pH 6 and increased metal ion concentrations

Microplastics as carriers of hydrophilic pollutants in an aqueous environment

Plastic materials such as polyethylene (PE), polyvinyl chloride (PVC), and polyamide nylon 6 (PN6) are extensively used worldwide. Significant quantities end up in the environment as waste, which gradually deteriorate and may travel for long distances. In this study, the capacity of these microplastics to sorb RR 120, an anionic dye commonly found in textile wastewaters, was investigated. PN6 showed the highest sorption capacity of 4.80 mg g−1, at a dose of 0.4 g and pH 2, whereas increasing the dose of the microplastic resulted in a gradual decrease of the sorption capacity for all materials. Increasing the dye concentration, resulted in higher sorption capacities. The FTIR analysis of the microplastics before and after sorption of RR 120, indicated no chemical bonding pointing out the absence of covalent bonds with specific surface groups of the microplastics in the sorption of RR 120. A plausible explanation for the highest sorption capacity of PN6 is the presence of N and O, which can readily form H bonds with the hydroxyl groups of RR 120

Thermal stability of solid and aqueous solutions of humic acid

The effects of temperature on the stability of a soil humic acid were studied in the present work. Solid samples of Gohy-573 humic acid (HA) and dissolved ones in aqueous solution (pH 6.0, 0.1 mol L−1 NaClO4) were investigated in order to understand the impact of temperature on the chemical properties of the material. The methods applied to solid samples in the present investigation were thermogravimetric analysis (TGA), temperature-programmed desorption coupled with mass spectrometry (TPD–MS), and in situ diffuse reflectance infrared Fourier transformed spectroscopy (in situ DRIFTS). Humic acid samples were studied in the 25–800 ◦C range, with focus on thermal/chemical processes up to 250 ◦C. The reversibility of the changes observed was investigated by cyclic changes to specified temperature ranges (40–110 ◦C). All measurements were conducted under inert-gas atmosphere in order to avoid samples combustion at increased temperatures. Aqueous solutions were analyzed by UV–vis absorption spectroscopy after storage at temperatures up to 95 ◦C, and storage times up to 1 week. For temperatures below 100 ◦C experiments on solid and aqueous samples have shown results which were consistent to each other. The amount of water desorbed is temperature dependent and up to 70 ◦C this process was totally reversible. Above 70 ◦C an irreversible loss of water was also observed, which according to UV–vis spectroscopy corresponds to water produced by condensation leading to more condensed polyaromatic structures. The water released up to 110 ◦C was about 7 wt% of the total mass of the dried humic acid, where less than 50% corresponded to reversibly adsorbed water. At higher temperatures (>110 ◦C), gradual decomposition resulting in the formation of carbon dioxide (110–240 ◦C), and carbon monoxide (140–240 ◦C) takes place. Hence, thermal treatment of Gohy-573 humic acid above 70 ◦C results in irreversible structural changes, that could affect chemical properties (e.g., complex formation) of the material

Alpha-radiometry of seawater by liquid scintillation counting

Liquid scintillation counting of the alpha-radionuclides after pre-concentration by cation-exchange represents a simple and robust method for the determination of total alpha-radioactivity in seawater. The total efficiency and the minimum detectable activity were calculated to be 95% and 30 mBq, respectively, for a liter sample and 1000-minute measuring time. The method has been applied successfully for the determination of alpha-radioactivity in seawater from five different coastal areas in Cyprus. The average alpha-radioactivity and uranium concentration were found to be 124±8 mBq·1-1 and 3.2±0.2 μg·1-1, respectively