Iron Oxide Nanomaterials for the Removal of Cr(VI) and Pb(II) from Contaminated River After Mariana Mining Disaster

If not properly treated, water contaminated with chromium (Cr(VI)) and lead (Pb(II)) can cause severe damage to health due to the accumulation of those toxic metals in the human body. Therefore, in this work, three iron oxides, i.e., δ-FeOOH, cystine-functionalized δ-FeOOH (Cys-δ-FeOOH), and Fe3O4, were synthesized and used as adsorbents for Cr(VI) and Pb(II) in water. The results indicated that the Cr(VI) is best adsorbed on cys-δ-FeOOH followed by δ-FeOOH and Fe3O4. It was because of the enhanced interaction between Cr(VI) and the cysteine functional groups on the δ-FeOOH surface. The Cr(VI) adsorption capacity of cys-δ-FeOOH, δ-FeOOH, and Fe3O4 was 217, 14, and 8 mg g−1, respectively. On the other hand, Pb(II) was preferentially adsorbed directly on δ-FeOOH achieving a maximum Pb(II) adsorption capacity of 174 mg g−1. The Pb(II) adsorption capacity of cys-δ-FeOOH and Fe3O4 was 97 and 74 mg g−1, respectively. The Cr(VI) adsorption on cys-δ-FeOOH was best described by the Langmuir-Freundlich model, whereas Pb(II) adsorption on δ-FeOOH followed the Langmuir model. Both Cr(VI) and Pb(II) adsorption on the adsorbents was well-fitted to pseudo-second-order kinetics. The Cr(VI) was more quickly adsorbed by cys-δ-FeOOH (h0 = 0.10 mg g−1 min−1) while the initial adsorption rate of Pb(II) onto δ-FeOOH was significantly faster (h0 = 16.34 mg g−1 min−1). Finally, the synthesized adsorbents were efficient to remove Cr(VI) and Pb(II) from water samples of the Doce river after the environmental disaster of Mariana city, Brazil, thus showing its applicability to remediate real water samples.

Nanoporous Activated Carbon Derived via Pyrolysis Process of Spent Coffee: Structural Characterization. Investigation of Its Use for Hexavalent Chromium Removal

Hexavalent chromium (Cr(VI)) is a heavy metal that is highly soluble and exhibits toxic effects on biological systems. Nevertheless, it is used in many industrial applications. The adsorption process of Cr(VI), using activated carbon (AC), is under investigation globally. On the other hand, around six million tons of spent coffee is sent to landfill annually. In the spirit of cyclic economy, this research investigated the production of AC from spent coffee for the removal of Cr(VI) from wastewater. The AC was produced via pyrolysis process under a nitrogen atmosphere. Chemical activation using potassium hydroxide (KOH) occurred simultaneously with the pyrolysis process. The produced AC was tested as an absorber of Cr(VI). The best fitted kinetic model was the diffusion–chemisorption model. A 24-h adsorption experiment was carried out using a solution with a pH of 3 and an initial Cr(VI) concentration of 54.14 ppm. This resulted in an experimental maximum capacity of 109 mg/g, while the theoretical prediction was 137 mg/g. It also resulted in an initial adsorption rate (ri) of 110 (mg/(g h)). The Brunauer–Emmett–Teller surface area (SgBET) was 1372 m2/g, the Langmuir surface area (SgLang.) was 1875 m2/g, and the corrugated pore structure model surface area (SgCPSM) was 1869 m2/g. The micropore volume was 84.6%, exhibiting micropores at Dmicro1 = 1.28 and Dmicro2 = 1.6 nm. The tortuosity factor (τ) was 4.65.

Modified Vermiculite as Adsorbent of Hexavalent Chromium in Aqueous Solution

The aim of this study was to investigate the efficiency of removing Cr6+ from aqueous solutions using two exfoliated vermiculite: (1) heated abruptly at 1000 °C and (2) irradiated with microwave radiation. The effects investigated were contact time, adsorbate concentration and initial Cr6+ concentration. The adsorption with both exfoliated vermiculites was well described by the DKR isotherm, indicative of a cooperative process and with the pseudo second order kinetic model. The Kd value for the two exfoliated vermiculites was similar, 0.2 ·1010 μg/Kg. The maximum adsorption capacity of Cr6+ with thermo-exfoliated vermiculite, 2.81 mol/g, was much higher than with microwave irradiated vermiculite, 0.001 mol/g; both values were obtained with 0.5 g of vermiculite in contact with distilled water enriched with 1 ppm of Cr6+ for 24 h. Factors such as ion chemistry, the solution pH and ionic strength, influence the values of capacity, adsorption energy and initial adsorption rate values of the exfoliated vermiculite. In addition, these values depended on the exfoliation process, being the adsorption capacity highest with abrupt heating of vermiculite, while the adsorption energy and rate values showed just a slight increase with microwave irradiation. This aspect is important to select the most suitable vermiculite modification treatment to use it as an adsorbent.

On the Understanding of the Adsorption of 2-Phenylethanol on Polyurethane-Keratin based Membranes

Polymers and specifically hybrid polymeric membranes have been identified as effective formulations in adsorption processes. Nevertheless, the adsorption mechanisms associated with their thermodynamics and kinetics are not fully understood, particularly when these polymeric membranes are used to adsorb 2-Phenylethanol (2-PE) to intensify its production in a specific bioconversion process. This work was aimed at giving phenomenological insights on the adsorption of 2-PE on a set of novel porous hybrid membranes based on polyurethane and keratin biofiber obtained from chicken feathers. Feathers, considered as a waste by-product of the poultry industry, represent an alternative source of keratin, a biopolymer that can be used to design low-cost materials from natural resources. Two types of hybrid membranes were prepared. i. e. composite and copolymer. Firstly, these materials were characterized by scanning electron microscopy (SEM), infrared spectroscopy (FT-IR) (before and after the adsorption process) and X-Ray (WAXD) analysis. Secondly, these materials, including the reference ones (keratin biofiber and polyurethane), were evaluated during the removal of 2-PE, relating their adsorption capabilities to physiochemical properties elucidated during the characterization. Particularly a composite with 0.1 g of chicken-feather-keratin (C1) presented the highest removal percentage (60.68%), a significant initial adsorption rate (0.2340 mgPE.h−1.gA −1), the maximum adsorption capacity (12.13 mgPE.gA −1) and the best stability and mechanical properties at studied operating conditions. In comparison with results reported in literature, in this composite carbonyl functional groups from polyurethane showed rather major affinity to 2-PE than amino groups from the keratin biofiber. To this end, parameters associated with its industrial application were obtained, namely thermodynamic and kinetic information was obtained from a proper design of experiments and phenomenological models based on adsorption macroscopic fundamentals.

Kinetics and adsorption isotherm of lactic acid from fermentation broth onto activated charcoal

Activated charcoal was applied for the recovery of lactic acid in undissociated form from fermentation broth. Lactic acid was obtained from the fermentation of Lactobacillus casei TISTR 1340 using acid hydrolyzed Jerusalem artichoke as a carbon source. The equilibrium adsorption isotherm and kinetics for the lactic acid separation were investigated. The experimental data for lactic acid adsorption from fermentation broth were best described by the Freundlich isotherm and the pseudo-second order kinetics with R2 values of 0.99. The initial adsorption rate was 41.32 mg/g?min at the initial lactic acid concentration of 40 g/L.

Polyaniline/reduced graphene oxide/Fe3O4 nano-composite for aqueous Hg(II) removal

To ease the adsorbent recovery and to increase the adsorption capacity of polyaniline (PANI), aniline was polymerized in the presence of a solvothermally prepared nano-composite of reduced graphene oxide and Fe3O4 (RGO/Fe3O4). The polyaniline was formed along the RGO/Fe3O4 composite in transmission electron microscope (TEM). The thus formed PANI/RGO/Fe3O4 adsorbent was tested and applied in removing Hg(II) in aqueous solution. The initial adsorption rate as well as the adsorption capacity increases with the incorporation of RGO/Fe3O4. The magnetic separation of PANI/RGO/Fe3O4 was easy, and its regeneration can be carried out at the optimal pH of 2. Test results proved the competence of the prepared adsorbent in pollution remediation applications for safer water quality and environmental protection.

Adsorption Kinetics of Cr (VI) onto Strong Alkaline Anion Exchange Fiber from Aqueous Solutions

The adsorption kinetics of strong alkaline anion exchange fiber for Cr (VI) from aqueous solutions was investigated. The adsorption was a fast process. Kinetics data for adsorption of Cr (VI) from aqueous solutions were in good agreement with the pseudo-second rate equation within an initial concentration range of 50-500 mgL-1. Both the equilibrium capacity and initial adsorption rate increased with an increase in Cr (VI) initial concentration. The adsorption process had combined control by chemisorption and physisorption, including film diffusion and intra-particle diffusion.

Kinetics and thermodynamics of adsorption of congo red on cellulose

Thermodynamics and kinetics of adsorption of congo red (CR) on cellulose are studied at 308–328 K. In the used concentration range of CR, interaction of CR with cellulose is exothermic and CR molecules adsorb chemically on cellulose surface. The effects of contact time, temperature and initial concentration of CR on kinetics of its adsorption on cellulose were investigated. The process proceeds according to the pseudo-second-order equation. Initial adsorption rate of adsorption is first-order in CR and the intraparticle diffusion of CR molecules within cellulose is identified as the main rate-limiting step.

Study on the Absorption Action of Modified Activated Carbon for Phenol

To improve the adsorption efficiency of activated carbon for phenol, copper nitrate was used to modify activated carbon. In detail, the absorption properties of modified activated carbon was studied by investigating the effects of adsorption time, pH, amount of modified activated carbon and initial concentration of phenol on the adsorption. And the dynamic and adsorbent model were obtained and explored. It shows that the removal rate of modified activated carbon for phenol was higher than the unmodified carbon, and the best removal rate can be obtained under the conditions of pH about 5, adsorption time of 2h, modified activated carbon dosage of 1.0g. The quasi-two rate equation was better to reflect the dynamics of modified activated carbon for phenol, with the initial concentration of phenol increased, equilibrium adsorption capacity and initial adsorption rate were greater. Both Freundlich and Langmuir model could reflect the adsorption behavior of modified activated carbon for phenol, while the Langmuir model was more properly.