Film Diffusion Model Research Articles

Biosorption of Cr(VI) by Theobroma cacao pericarp.

This paper reports a comprehensive study of Theobroma cacao pericarp (TCP) residues, which has been prepared, characterized, and tested as an inexpensive and efficient biosorbent of Cr(VI) from aqueous solutions. The maximum adsorption capacity of TCP obtained at optimal conditions (pH = 2, dose = 0.5g L-1, C0 = 100mg L-1) was qmax = 48.5mgg-1, which is one of the highest values reported by the literature. Structural and morphological characterization has been performed by FTIR, SEM/EDX, and pHPZC measurements. FTIR analysis revealed the presence of O-H, -NH, -NH2, C = H, C = O, C = C, C-O, and C-C functional groups that would be involved in the Cr(VI) biosorption processes. The experimental equilibrium data of biosorption process were successfully fitted to non-linear Langmuir (R2 = 0.95, χ2 = 11.0), Freundlich (R2 = 0.93, χ2 = 14.8), and Temkin (R2 = 0.93, χ2 = 14.7) isotherm models. Kinetics experimental data were well adjustment to non-linear pseudo-2nd (R2 = 0.99, χ2 = 2.08)- and pseudo-1st-order kinetic models (R2 = 0.98, χ2 = 2.25) and also to intra-particle Weber-Morris (R2 = 0.98) and liquid film diffusion (R2 = 0.99) models. These results indicate that Cr(VI) biosorption on heterogeneous surfaces as well as on monolayers of TCP would be a complex process controlled by chemisorption and physisorption mechanisms. The thermodynamic results indicate that the Cr(VI) biosorption on TCP is a feasible, spontaneous, and endothermic process. TCP can be regenerated with NaOH and reused up to 3 times.

The Bioremoval of Toxic Dyes Using Chlorella Algae in Airlift Bioreactor

<p style="text-align:justify; margin-bottom:11px"><span style="font-size:11pt"><span style="line-height:107%"><span style="font-family:Calibri,sans-serif"><span style="font-size:14.0pt"><span style="line-height:107%"><span style="font-family:"Times New Roman",serif">Malachite green (MG) and Crystal Violet (CV) are used mainly as dyestuff and antimicrobials in aquaculture. They have a severe toxic effect on the environment. Several techniques were used to remove impurities from an aqueous solution: chemical, physical, and electrical. Among all these techniques, using dry algae is a more economical and helpful process. This study aims to investigate using an airlift reactor in the removal of MG and CV by chlorella algae as a biosorbent under different variables. The experiments were carried out in an airlift bioreactor. The experiments were carried out under the effect different operating conditions of initial dye concentration (5-40 ppm), alga dosage (0.3-1.8 gm/l), pH (3–10), air flow rate (0-40 ml/min), temperature (298-318 K) and contact time (5-60 min).  The results show that the introduce of air bubbles significantly enhances the removal efficiency of the dye. The best removal effectiveness was 95.2% for MG dye and 96.1% for CV dye.  The thermodynamics results reveal that the processes are exothermic for both dyes. Kinetic and adsorption isotherms results show the best fit is pseudo-second order and Langmuir model. The mass model result shows that the liquid film diffusion model was the best-fitted for both dyes.</span></span></span></span></span></span></p>

Boyd’s film diffusion model for water contaminant adsorption: Time for an upgrade?

The Boyd film diffusion model is widely used in liquid phase adsorption studies for its mathematical simplicity and straightforward data analysis. However, a lack of awareness regarding its restrictive assumptions has led to widespread misuse. The Boyd model assumes film diffusion as the rate-controlling mechanism and rests on two additional pivotal assumptions: adsorption occurs under infinite bath conditions and follows a linear equilibrium relationship. This study examines the recurrent breaches of these assumptions across a growing body of research on water contaminant adsorption. Nearly all kinetic data have been derived from finite bath experiments governed by nonlinear isotherms, which directly contradict the Boyd model’s assumptions. Consequently, applying the Boyd model to such data can yield misleading results and interpretations. To address these challenges, alternative models tailored for finite bath conditions and capable of accommodating both linear and nonlinear isotherms should be considered. These models offer more accurate insights into adsorption kinetics under realistic experimental settings. While the Boyd model remains valuable under specific conditions, its stringent assumptions restrict its broader applicability. Researchers should critically assess the validity of these assumptions and explore alternative models when analyzing liquid phase adsorption kinetics to ensure robust and reliable results.

Concentration polarizations of PEG and silica colloids in ceramic nanofiltration

A large decrease in permeability is often observed during the filtration of nano-sized colloids, while fouling is widely regarded as the main explanation for this phenomenon. The osmotic pressure or concentration polarization (CP) of colloids can also contribute to the flux decline. However, the contribution of CP to flux loss cannot be determined by the traditional CP model. In this study, the effect of fouling and CP/osmotic pressure on flux was distinguished. The CP values of polyethylene glycol (PEG) and silica-colloids were determined by the osmotic pressures near the membrane surface and in the feed. The CP induced by colloids accounted for 43–95% of the flux loss in our experiments. Silica exhibited higher CP values (127–460), compared to 7–71 for PEG. This was attributed to the slower back diffusion caused by the larger colloids, as evidenced by the diffusion coefficients of 4.30 × 10−11 m2/s for silica (10 nm) and 1.45 × 10−10 m2/s for PEG (2.9 nm). Although the CP was mitigated by increasing the cross-flow velocity, CP values of 31 and 250 were observed for PEG and silica at high Reynolds number of 7317, respectively. The experimentally obtained CP values were also compared with those calculated by the film diffusion model.

Exploring kinetic and thermodynamic insights of graphene related two dimensional materials for carbon dioxide adsorption

Graphene related two dimensional materials (GR2Ms) are promising adsorbents for CO2 capture. However, the CO2 adsorption kinetics and mechanisms on these materials remain insufficiently explored and understudied. Recognizing the pivotal role of adsorption kinetics in assessing the practical applicability, this study comprehensively evaluates the CO2 adsorption kinetics, underlying mechanisms, and thermodynamic properties via gravimetric analysis on three distinct well-characterized graphene materials (few layer graphene-FLG, graphene oxide-GO, reduced graphene oxide-rGO) across temperatures from 25 to 75 °C under atmospheric pressure. Results reveal that Avrami’s fractional model offers the most accurate fit for CO2 adsorption kinetics among the three examined models (pseudo-first, pseudo-second, and Avrami’s fractional order). The interplay between the physico-structural-chemical properties of GR2Ms and the CO2 adsorption kinetics discloses that the morphology, crystallite size, specific surface area and porosity of GR2Ms greatly influence the CO2 adsorption rate as evidenced by the largest rate constant, kA value of rGO at 25 to 75 °C under atmospheric pressure. Analysis of activation parameters including activation energy, enthalpy of activation, entropy of activation, and free energy of activation derived from Eyring, Arrhenius, and Gibbs equations indicates a greater favorability of CO2 adsorption on GR2Ms at lower temperatures. Moreover, investigation into the underlying interaction mechanisms between CO2 molecules and GR2Ms, using rate-limiting kinetic models (Boyd’s film diffusion model, interparticle diffusion model, and intraparticle diffusion model), confirms that both film diffusion resistance and intraparticle diffusion resistance predominantly govern the CO2 adsorption rate.

Preparation of poly(divinylbenzene-co-methyl acrylate) adsorbent with tunable surface hydrophilicity for atrazine removal

To efficiently remove atrazine, it is crucial to facilitate synergistic adsorption effect between aromatic structure and hydrophilic adsorption sites through tuning surface hydrophilicity. Herein, we reported a polymer adsorbent which was synthesized by copolymerizing divinylbenzene (DVB) and methyl acrylate (MA) with different monomer ratio, and subsequently hydrolyzing the copolymer to obtain carboxyl group on its surface. The surface hydrophilicity could be easily adjusted by changing the ratio of monomer and the optimal feeding ratio was 4:1 (VDVB:VMA) in terms of porosity (specific surface area 712.92 m2/g) and hydrophilicity regarding atrazine adsorption. The adsorption process followed the Langmuir isotherm with a maximum adsorption capacity of 75.75 mg/g. The mixed surface reaction and film diffusion model revealed that the adsorption procedure is dramatically controlled by film diffusion. Atrazine molecules diffusive and bound with porous adsorbent via strong hydrogen bonding between N (triazine and amine) and carboxyl groups introduced by copolymerization. Furthermore, high porosity caused by aromatic crosslinked network provided sufficient adsorption sites through π-stacking interaction. This work not only supplies a highly efficient adsorbent for atrazine removal but also enables a platform for preparation of polymers with tunable porosity and surface hydrophilicity.

Fabrication of date palm kernel biochar-sulfur (DPKB-S) for super adsorption of methylene blue dye from water

A novel form of biochar was created by dehydration of Date palm kernel with 85% sulfuric acid. It was examined how the newly produced biochar (DPKB-S) affected the aqueous solution's capacity to extract Methylene Blue (MB) dye. The prepared DPKB-S was categorized by BET, BJH, FT-IR, SEM, EDX, DSC, and TGA analyses. The ideal pH for the MB dye adsorption by DPKB-S is 8. With 0.75 g L−1 of DPKB-S and an initial concentration of 50 ppm MB dye, Date Palm Kernel Biochar-Sulfur (DPKB-S) had the highest removal percentage of 100%. The Langmuir and Freundlich isotherm models were used to investigate the collected data. Freundlich model is the model that best covers MB dye adsorption in DPKB-S at low concentrations (0.75–1.25 g L−1) and the Langmuir model at high concentrations (1.5–1.75 g L−1). The Langmuir model maximum adsorption capacity (Qm) of the DPKB-S was 1512.30 mg g−1. Furthermore, a variety of error function models were applied to investigate the isotherm models derived data, including Marquardt’s percent standard deviation (MPSD), the sum of absolute errors (EABS), the sum of the errors squared (ERRSQ), root mean square errors (RMS), Chi-square error (X2), the average relative error (ARE), average percent errors (APE), and hybrid error function (HYBRID). Kinetic data were calculated by intraparticle diffusion (IPD), pseudo-second-order (PSO), pseudo-first-order (PFO), and film diffusion (FD) models. A PSO rate model with a strong correlation (R2 = 1.00) largely regulated the adsorption rate. The removal mechanism of MB dye by DPKB-S is based on the principle that these positively charged dyes are attracted by electrostatic attraction forces due to the growth in the number of negatively charged regions at basic pH value. According to the results, DPKB-S shows promise as an affordable and competent adsorbent for the adsorption of MB dye. It can be used frequently without experiencing a discernible decrease in adsorption efficiency.

KINETICS AND MECHANISM MODELLING OF Pb(II) AND Ni(II) IONS SORPTION FROM AQUEOUS MEDIUM: EVALUATING THE PERFORMANCE OF Curcuma longa RHIZOME IN THE TREATMENT OF WASTE WATER.

In this research Curcuma longa Rhizome, an agricultural product, available in large quantity in northern Nigeria, were used as low-cost adsorbent for removal of Pb(II) and Ni(II) ions from aqueous medium. Batch operation was used to study the equilibrium behaviour of Curcuma longa rhizome. The effect of solution pH, and contact time on the adsorbent for the removal of Pb(II) and Ni(II) ions were evaluated. To study the adsorption kinetics of Pb(II) and Ni(II) ions onto Curcuma longa Rhizome, pseudo-first-order, pseudo-second-order as well as three diffusion models: intraparticle diffusion model (Weber and Morris model), film diffusion model (McKay model) and liquid film Models were used. The sorption kinetics can be described well by the pseudo-second-order model due to the closeness between the qexp ( 49.26 mg/g) and qcal (52.63 mg/g) for Pb(II) and qexp (57.60) and qcal (55.56 mg/g) for Ni(II) ions. Moreover, the rate limiting step are liquid film and intraparticle diffusion controlled. In addition, the results suggest that Curcuma longa Rhizomes are very effective adsorbent for the removal of Pb(II) and Ni(II) ions from aqueous medium. This will serve as an indicator to consider in the design for waste water treatment plant for heavy metal detoxification using Curcuma longa Rhizome.

Kinetic and mechanistic study of CO2 adsorption on activated hydrochars

Four activated hydrochars (AHCs) were obtained by hydrothermal carbonization of pine sawdust followed by physical and chemical activation in mild conditions. The effects of the activating agents on the porous structure of AHCs were analysed using nitrogen adsorption isotherms. Their CO2 adsorption capacity was assessed by means of carbon dioxide isotherms at 25 and 50 ºC and thermogravimetry, and compared with a commercial activated carbon (AC). SBET values greater than 2000 m2/g were obtained. A narrow micropore volume of 0.392 cm3/g was obtained for the hydrochar activated with KHCO3. The highest CO2 uptake of 3.3 mmol/g (145.2 mg/g) was obtained at room temperature (25 ºC) for the hydrochar activated with KHCO3. Three kinetic models (pseudo-first, pseudo-second and fractional order Avrami’s models) were used to examine the rate parameters of CO2 uptake, with Avrami’s model giving the most accurate prediction of CO2 adsorption. The intraparticle diffusion model and Boyd’s film-diffusion model were applied to identify the CO2 adsorption mechanism.

Kinetics of sphalerite dissolution for potential zinc recovery via oxidative leaching

ABSTRACT In this study, the leaching of zinc from sphalerite in nitric acid (HNO3)/hydrogen peroxide (H2O2) binary solution was examined via kinetic study. The result showed that the amount of zinc leached increased as the temperature and leachant concentration increased, from 53.8 to 91% for H2O2 concentrations of 2 and 10 M; 53 to 93.2% for temperature of 30 and 90°C, respectively, and decreased as the solid/liquid ratio and particle diameter increased from 92.3 to 55.9% for S/L ratios of 20 and 50 g/L; 93.4 to 51.1% for particle diameters of <75 µm and <425 µm, respectively. The solid film diffusion model provided the finest description of the experimental data while chemical reaction was established as the rate-limiting step, with activation energy of 26.52 kJ/mol. Hence, a binary solution of HNO3 and H2O2 was established as a viable route towards recovering zinc from sphalerite.

Comprehensive analysis of cationic dye removal from synthetic and industrial wastewater using a semi-natural curcumin grafted biochar/poly acrylic acid composite hydrogel.

Polymer composites offer a tailored framework as an exceptional candidate for water treatment due to their tunable chemical structure, porous 3D architecture, physiochemical stability, accessibility, pH-sensitivity and ease of use. In this study, curcumin-engineered biochar is embedded into a cross-linked polyacrylic acid hydrogel matrix using in situ polymerization for developing a semi-natural adsorbent for the removal of cationic dye from an aqueous solution. The physicochemical features of the generated composite hydrogel are significantly influenced by the implementation of curcumin-grafted biochar into the polyacrylic acid substrate. Comprehensive characteristic approaches were employed to explore all aspects of the adsorbent's properties, especially its removal efficacy. The methodical adsorption study was accomplished by monitoring dynamic factors such as pH, adsorbent content, time frame, and initial dye concentration. The presence of the porous aromatized structure of biochar, active oxygen-enrich functional groups (carboxyl, hydroxyl, keto, enol, ether) coupled with the conjugated curcumin structure facilitate the effective establishment of hydrogen bonds, electrostatic interactions, π-π interactions, electron donor-acceptor and charge-assisted H-bonding with the malachite green (MG) and rhodamine B (Rho) molecules. The highest adsorption capacities of MG and Rho reached 521 mg g-1 and 741 mg g-1 respectively, in the range of neutral pH, considering their molecular nature, functionalities, and unique adsorption mechanisms. The isothermal modeling was carried out with Henry, Langmuir, Jovanovic, Freundlich, Temkin, and Koble-Corrigan models to determine the adsorption system. Additionally, the kinetic data were assessed with Bangham, pseudo-first-order, pseudo-second-order, intra-particle, and liquid film diffusion models to ascertain the rate-limiting phase. The Koble-Corrigan and Langmuir isotherm models (R2 > 0.997) as well as pseudo-second-order (R2 > 0.998) and Elovich (R2 = 0.983 and 0.995) kinetics models provide a substantial level of concordance with empirical findings. The analysis of non-linear diffusion models revealed that the Bangham (R2 > 0.995) pore and liquid film diffusion (R2 > 0.960) models has major influence on the rate of the adsorption procedure. The binary adsorption test demonstrated higher efficacy of the synthesized adsorbent in the removal of malachite as compared to rhodamine. This study sheds light on the design of a cost-effective semi-natural polymeric composite for treating dye-polluted wastewaters, a major milestone toward environmental and ecological sustainability.

Adsorption properties of M-UiO-66 (M = Zr(IV); Hf(IV) or Ce(IV)) with BDC or PDC linker.

The increasing CO2 emissions and their direct impact on climate change due to the greenhouse effect are environmental issues that must be solved as soon as possible. Metal-organic frameworks (MOFs) are one class of crystalline adsorbent materials that are thought to have enormous potential in CO2 capture applications. In this research, the effect of changing the metal center between Zr(IV), Ce(IV), and Hf(IV), and the linker between BDC and PDC has been fully studied. Thus, the six UiO-66 isoreticular derivatives have been synthesized and characterized by FTIR, PXRD, TGA, and N2 adsorption. We also report the BET surface area, CO2 adsorption capacities, kinetics, and the adsorption isosteric heat (Qst) of the UiO-66 derivatives mentioned family. The CO2 adsorption kinetics were evaluated using pseudo-first order, pseudo-second order, Avrami's kinetic models, and the rate-limiting step with Boyd's film diffusion, interparticle diffusion, and intraparticle diffusion models. The isosteric heats of CO2 adsorption using various MOFs are in the range 20-65 kJ mol-1 observing differences in adsorption capacities between 1.15 and 4.72 mmol g-1 at different temperatures due to the electrostatic interactions between CO2 and extra-framework metal ions. The isosteric heat of adsorption calculation in this report, which accounts for the unexpectedly high heat released from Zr-UiO-66-PDC, is finally represented as an increase in the interaction of CO2 with the PDC linker and an increase in Qst with defects.

Simultaneous removal of triadimefon and dinotefuran by a new biochar-based magnesium oxide composite in water: Performances and mechanism

In recent years, the ecological security has been seriously threatened by the residues of pesticides in the environment. In this study, a new biochar-based magnesium oxide composite (MTBC) was successfully prepared using Traditional Chinese Medicine residues and MgCl2 solution, and then applied for the removal of triadimefon (TDF) and/or dinotefuran (DIN) in water. Batch experiments results indicated that 86.42 and 87.86 % of TDF and DIN removals could be obtained by MTBC within 120 min, respectively. The TDF adsorption process was proved to be well fitted with the pseudo-second-order kinetic, Elovich, liquid film diffusion, Intra-particle diffusion and Langmuir isothermal models. The TDF adsorption by MTBC was a spontaneous endothermic reaction, and chemical adsorption process was dominant. The inhibitory of the coexisting anions on TDF removal followed the order of SO42−＜Cl−＜HPO43−＜HCO3–. Both TDF and DIN could be simultaneously removed by MTBC at the certain concentrations levels. The possible removal mechanism for the adsorption of TDF and DIN by MTBC was proposed, both TDF and DIN were rapidly distributed and adsorbed on MTBC surface, then diffused into the interior pores structure and were finally adsorbed on MTBC through various reaction processes. The TDF removal process might be involved with hydrogen bonding, π-π interaction, pore filling and electrostatic interaction, while DIN removal might be involved with hydrogen bonding, pore filling and electrostatic interaction. These findings suggested that biochar-based magnesium oxide composite was an effective adsorbent for the remediation of agricultural effluents containing TDF and DIN.

Kinetics of Owhe kaolinite leaching for alumina recovery in hydrochloric acid solution

Recovery of alumina from kaolinite presents a sustainable alternative to its recovery from bauxite, a major source of alumina which is depleting in quantity globally. Owhe kaolinite proves to be a reliable resource for this process given its rich alumina content. This study focused on the leaching of alumina from Owhe kaolinite in hydrochloric acid (HCl) solution. Effects of parameters such as acid concentration, stirring rate, leaching temperature, particle diameter and solid/liquid (S/L) ratio, were investigated. The experimental data was analyzed using relevant kinetic models to establish the best model of fit. Alumina leaching rate increased as the temperature, stirring rate, and acid concentration increased, and decreased with increase in solid/liquid ratio and particle diameter. The experimental results fitted into the solid film diffusion model while chemical reaction was found to be the rate-determining step, with activation energy (Ea) of 34.79 kJ/mol and a pre-exponential factor of 120.37 s–1. The result revealed an average alumina leaching rate of 85 % with an overall reaction constant of 0.983 s–1. Post-leaching analysis by energy dispersive spectrophotometer (EDS) also confirms over 80 % alumina leaching rate, which is in line with the experimental result. Hence, hydrochloric acid proved to be a viable lixiviant for alumina recovery from Owhe kaolinite.

Mass transport, kinetic model, and application of CO2 adsorption on zeolite 5A granules

AbstractEnvironmental damage ranges from soil degradation, air pollution, and wastewater from human‐induced activity. In this study, to reduce CO2 emission, zeolite granules were prepared manually. In addition, the mass transfer and kinetic adsorption were analyzed to understand the mechanism of CO2 adsorption using mathematical models. We studied the effects of amount of binder, temperature, granule size, and flow rate of CO2 on efficient CO2 adsorption on zeolite 5A granules of different sizes (3–4 and 6–7 mm). The kinetics of CO2 adsorption and mass transfer of zeolite 5A granules were evaluated for the rate‐limiting step. The results showed that decreasing the temperature and the amount of binder increased the CO2 adsorption capacity. We observed the highest CO2 adsorption capacity of 2.84 mmol g−1 at 298 K with 4 wt% of the binder at a flow rate of 2 L h−1. The pseudo‐first‐order sorption behavior was the best model with R2 &gt; 0.9832, whereas the root mean square error model showed an R2 &lt; 0.2136. The Biot number and film diffusion model were used to investigate the importance of external mass transfer on intraparticle diffusion. It was confirmed that the adsorption on sustainable zeolite 5A granules was controlled by film diffusion.

Modeling of CO2 Adsorption on Surface-Functionalized Rubber-Seed Shell Activated Carbon: Isotherm and Kinetic Analysis

Currently, adsorption is considered a promising technology for CO2 separation with a wide range of adsorbents. A detailed study of equilibrium and kinetics plays a crucial role in the design and operation of industrial adsorption units. In this study, isotherm and kinetics of CO2 adsorption on two RSS-derived AC samples previously prepared in our laboratory were evaluated using equilibrium experiments for pure CO2 at 25 °C and 40 °C and 1 bar. Blank and IL-functionalized AC showed CO2 adsorption capacity of 2.16 mmol/g, 1.96 mmol/g, 1.12 mmol/g and 1.71 mmol/g at 25 °C and 40 °C, respectively. Langmuir, Freundlich, and Temkin equations were used to model adsorption isotherm in low-pressure regions. The obtained results revealed that the Freundlich model provides an accurate fitting to the experimental findings, which indicate that the adsorption process occurs in a heterogeneous phase. Additionally, kinetic analysis was performed by using four empirical models, namely pseudo-first order, pseudo-second order, Elovich, and Avrami’s fractional models. Among the considered kinetic models, the pseudo-second order model fits best for both blank and IL-functionalized AC. Intra-particle and Boyd’s film diffusion models were evaluated for the adsorption mechanism.

In-situ synthesis of efficient ZnCl2 doped pyrolyzed biochar for adsorptive remediation of organic dyes: Performance evaluation, mass transfer and mechanism

Effective management of harmful contaminants from waste effluent is crucial for a sustainable environment. Herein, the efficient adsorbent, sawdust-derived biochar doped with ZnCl2 (Z@SB) for removal of organic dyes, namely malachite green (MG) and methyl orange (MO), was explored via batch adsorption study. A detailed characterization of the synthesized adsorbent was conducted to determine its physiochemical properties. The specific surface area of Z@SB from BET analysis improved 5.66 times after chemical modification. Moreover, the decolorization efficiency of the dyes onto Z@SB was investigated through analyzing the impact of initial pH, adsorbent dose, and contact time of the process. The Langmuir isotherm analysis revealed the maximum adsorption capacity (Qmax) of MG and MO dyes were 318.47 and 225.73 mg/g, respectively. The adsorption kinetics data of both dyes was well described by the pseudo-second-order model. Furthermore, Boyd's film diffusion model was employed to assess the diffusion mechanism and determine the rate-limiting step using the kinetic data obtained from batch adsorption experiment. Possible mechanisms for the removal of dyes onto Z@SB included hydrogen bonding, π-π bonding, and electrostatic interactions. The superior regeneration and reusability properties observed in Z@SB make it a highly promising adsorbent for effective utilization in real-field wastewater treatment applications.

Characterization of the micro-interfacial interactions of heterogeneous particulate matter (fine-grained sediment and microplastics) with copper ions

Particulate matter, such as sediment and microplastics (MPs), in aqueous environments has comparable micro-interfacial characteristics. However, the micro-interfacial characteristics of heterogeneous particulate matter are complex and are not fully understood. In this study, micro-interfacial kinetics and the interactions governing copper (Cu) ion adsorption to PP–sediment were investigated using micro-interfacial characterization experiments and kinetic experiments for Cu ion absorption to sediment, polypropylene (PP), and PP–sediment particles. The results show that (1) a pseudo-second-order model can be used to accurately describe the micro-interfacial kinetics of Cu ion adsorption to PP–sediment, indicating that chemical adsorption dominates the process. For Cu, the adsorption capacity, qe, of PP–sediment is approximately 0.4808 mg/g, between that of sediment and PP. (2) Film diffusion is the rate-controlling process in the early adsorption stage. Intraparticle diffusion gradually becomes the controlling process as the film diffusion constant (kfd) decreases and the film diffusion model becomes less applicable, but intraparticle diffusion is weaker in the PP–sediment system than in the sediment-only system. (3) The applicability of the intraparticle diffusion model for Cu ion adsorption to PP–sediment in the later stage of adsorption is between that of the sediment and PP systems. Furthermore, the heterogeneous aggregation of sediment and PP affects the micro-interfacial interactions of both types of particulate matter. The current study contributes to a better understanding of the micro-interfacial interactions of heterogeneous particulate matter (such as fine-grained sediment and MPs) with heavy metal ions in aqueous environments.

α-Zirconium(IV) Phosphate: Static Study of 225Ac Sorption in an Acidic Environment and Its Kinetic Sorption Study Using natEu as a Model System for 225Ac.

Zirconium phosphate (ZrP), especially its alpha allotropic modification, appears to be a very promising sorbent material for the sorption and separation of various radionuclides due to its properties such as an extremely high ion exchange capacity and good radiation stability. Actinium-225 and its daughter nuclide 213Bi are alpha emitting radioisotopes of high interest for application in targeted alpha therapy of cancer. Thus, the main aim of this paper is to study the sorption of 225Ac on the α-ZrP surface and its kinetics, while the kinetics of the sorption is studied using natEu as a non-radioactive homologue of 225Ac. The sorption properties of α-ZrP were tested in an acidic environment (hydrochloric and nitric acid) using batch sorption experiments and characterized using equilibrium weight distribution coefficients Dw (mL/g). The modeling of the experimental data shows that the kinetics of 225Ac sorption on the surface of α-ZrP can be described using a film diffusion model (FD). The equilibrium weight distribution coefficient Dw for 225Ac in both hydrochloric and nitric acid reached the highest values in the concentration range 5.0-7.5 mM (14,303 ± 153 and 65,272 ± 612 mL/g, respectively). Considering the results obtained in radioactive static sorption experiments with 225Ac and in non-radioactive kinetic experiments with natEu, α-ZrP seems to be a very promising material for further construction of a 225Ac/213Bi generator.

Isotherm and kinetic investigations of sawdust-based biochar modified by ammonia to remove methylene blue from water

Chemical industry effluent may pose significant environmental risks to both human health and the economy if it is not properly managed. As a result, scientists and decision-makers are paying increasing attention to developing a sustainable, low-cost wastewater treatment technique. This work aims to investigate the adsorption of Methylene Blue (MB) dye present in water using biochar derived from sawdust modified by boiling in an ammonia solution (SDBA). The properties of SDBA were characterized by BET, SEM, XRD, BJH, FT-IR, DTA, EDX and TGA analyses. The presence of –OH and –NH groups in SDBA was confirmed by FTIR, which proved that the NH4OH treatment of biochar successfully added nitrogen groups on its surface. The influence of pH (2 to 12), MB dye initial concentration (20 to 120 mg/L), adsorbent dosage (0.5 to 4.0 g/L) and contact time (0 to 180 min) on the adsorption process has been investigated. The adsorption of MB dye is more favorable at basic pH, with optimum adsorption at pH 8. Using a starting concentration of 20 mg/L of MB dye and a 4.0 g/L SDBA dose, the maximum percent clearance of MB dye was 99.94%. Experimental results were fitted to the Freundlich (FIM), Tempkin (TIM) and Langmuir (LIM) isotherm models (IMs). The FIM fitted the equilibrium data well, with a 643.74 mg/g Qm. Various error function models were used to test the data obtained from IMs. According to Error Function results, experimental data showed that it fits better for LIM and FIM. Kinetic studies indicated that the MB dye adsorption procedure followed pseudo-second-order (PSOM) kinetics based on film diffusion (FDM), pseudo-first-order (PFOM) and intra-particle diffusion models (IPDM). MB dye sorption on the SDBA involved electrostatic interaction, surface participation, hydrogen bond and π–π interactions. The adsorption mechanism of MB dye by SDBA was proposed as physical adsorption via the electrostatic attraction process. SDBA is an effective adsorbent in removing MB dye from water. Six adsorption–desorption cycles of the MB dye were run through the regeneration of SDBA with only a minimal amount of adsorption capacity loss, demonstrating the reusability of manufactured SDBA.