Sorption mechanism of copper ions on synthetic and natural dentine hydroxyapatites

Removal of copper ions from aqueous solutions on synthetic and dentine waste hydroxyapatites (HAP) was investigated in batch sorption experiments. Kinetics of sorption followed a pseudo-first order model. Steady-state data show agreement with the Sips isotherm compared with Freundlich and Langmuir models. The higher surface area and carbonated nature of synthetic hydroxyapatite were not sufficient to reach higher sorption capacity than natural one. Ion-exchange and precipitation contributed on  removal of Copper despite level ionization of hydroxyapatites. Proton and metal exchanges with copper ions contributed to process of sorption with prevalence of proton-exchange at low copper ion concentrations. High temperatures promoted the removal efficiency of Cu(II) onto the natural and synthesised hydroxyapatites. The thermodynamic parameters showed that sorption process was spontaneous, endothermic and associated entropy at the solid/solution interface increased at high temperatures

Modelling CO2 adsorption in a thin discrete packing

Local dynamics of CO2 adsorption in a discrete packing contained in a thin tube was assessed by 3D modelling. Thin tube packed bed adsorbers are currently used over tube structures in thermochemical energy storage systems and atmospheric revitalization of confined spaces. Driven by interplays between key factors such as the exothermicity and the fluid flow, the advective transport was found less effective than the diffusive one on the breakthrough trends of CO2 which displayed significant concentration gradients at both inter- and intra-particle scales. The lack of angular symmetry inside the particles by the reduction in resistance to mass transfer in area of solid particles exposed to high velocities led to greater convective transports from bulk of the gaseous phase to the pores. The result of the modelling agreed with the experimental data obtained at the exit of the adsorber, helping reduction in reliance on the empirical dispersion models used in the one-dimensional modelling

Modelling the reaction of uranium with carboxylic groups on surfaces through mono- and multi- dentate surface complexes on the basis of pH and redox potential

An analytical expression is proposed to simulate effects of pH and redox potential (E) on the sorption of uranium onto bioorganic model particles in saline or other aquatic environments. The elaborated expression is intended to avoid use of the classical approach of sorption which relies on experimental data and empirical models. The goal is to produce an expression that provides a distribution coefficient (Kd e.g. mL g-1) as function of pH, E and ligand concentration (through complex formation in solution) by applying a surface complexation model on one type of mono-dentate surface sites >(SuOH) as well as utilizing multi-dentate surface sites >(SuOH)c. The formulation of the worked out expression makes use of correlations between the surface complexation and hydrolysis constants for all species and sorption sites. The model was applied to the sorption of uranium onto bioorganic sites with and without carbonates in solution e.g. Log Kd: +2.75 at pH 8 for 2 sites per nm2. The calculated distribution coefficients were found very sensitive to the presence of carbonates, e.g. Log Kd: -7.0 at pH 8 for 2×10-3 M total carbonate. The potential reduction of uranium U(VI) and its complexes (carbonates) which are the primary stable species in surface waters, to U(IV) during sorption was simulated in association with a decrease in the redox potential and was found generally below the redox stability limits of water. The calculated distribution coefficient values were validated by the values reported in literature for the sorption of uranium onto specific adsorbents. The investigated simulations are also applicable to the sorption of other redox sensitive elements

Reaction of uranium with poly-hydroxy-aromatic groups on particles through mono- and multi-dentate surface complexes on the basis of pH and redox potential : A modelling approach

redox potential (E) on the sorption of uranium onto potentially redox active bioorganic model particles in saline or other aquatic environments. Specifically herein, it is applied to the mono- and poly-hydroxy-aromatic (polyphenolic) sites which account for approximately 30% of bioorganic site capacity. The derived expression is aimed to avoid use of the classical approach of sorption, which requires experimental data and empirical models. The expression provides a distribution coefficient (Kd e.g. mL g−1) as function of pH, E and soluble ligand concentration by considering a surface complexation model on mono- or multi-dentate complexation surface sites > Su(OH)c. The application of the model uses correlations between the surface complexation constants and hydrolysis constants, for all potential species and all form of sorption sites. The model was used to quantify the uranium sorption onto hydroxy-benzene, dihydroxy- enzene, and dihydroxy-naphthalene sites with or without carbonates in solution. The latter is the primary interfering reagent in waters that decreases Log Kd. The calculated distribution coefficients were found sensitive to both pH and E and very sensitive to the presence of carbonates. The reduction of uranium U(VI), and its carbonate complexes, to U(IV) during sorption was simulated by decreasing the redox potential. It was found that the transition phase between U(VI) and U(IV) was generally below the redox stability limits of water. However, the reduction of U(VI) to U(IV) was found to be potentially associated with their reaction with the polyphenols, decreasing the redox potential subsequently. The calculated sorption coefficient values were validated using the values reported in literature for the sorption of uranium onto specific adsorbents. The methodology of the simulation is also applicable to the sorption of other redox sensitive elements, and with the addition of a scaling factor, it would allow the predictions of co-complexation phenomena by employing relevant site formulations. The oxidation of mono-hydroxy- benzene in di-hydroxy-benzene enhances the sorption of uranium by a factor 106 which may be applied to its extraction from seawater

Photodegradation of phenol in rotating disk reactor and 3D CFD modelling

Phenol is a chemical that is associated with the regulations in place that control the release of contaminants to the water environment. The photocatalytic degradation as advanced oxidation process is seen among the promising routes for reduction of a wide range of organic pollutants. This work investigates the degradation of phenol in a rotating disc reactor (RDR) as process intensification approach and highlights the role of the process parameters and relevant impacts on both mass transfer effectiveness and reaction rate performance over the essential role of oxygen penetration in the liquid film, the surface reaction catalyzed by the intermediate hydroxyl radicals and the UV light activation. Ensuring a sufficient supply to the catalyst surface is achieved by the thin film subject to the dynamic operations of the rotating disk and the deep light penetration across the bulk liquid film. This work aims to assess via a laboratory work the impact of hydrodynamics generated by the rotational speed and flow dyn

A novel hybrid enhanced oil recovery technique to enhance oil production from oil-wet carbonate reservoirs by combining electrical heating with nanofluid flooding

Enhanced Oil Recovery provides a promising technique to maximise fossil fuel recovery from existing resources, and when used in conjunction with Carbon Capture and Storage/Utilisation provides a way to support a transition to alternative cleaner fuels. A hybrid Enhanced Oil Recovery method by a combination of electrical heating and nanofluid flooding was applied to oil-wet carbonate reservoirs and assessed in terms of the oil production, zeta potential, contact angle, pellet compaction, interfacial tension, and pH values. The hybrid technique consisted of a combination of direct current (up to 30 V) and iron oxide (Fe2O3) or magnesium oxide (MgO) nanofluids. Both nanofluids were injected into oil-wet Austin chalk – our laboratory model of an oil-wet carbonate reservoir – and then electrical heating was started, or vice versa. Introducing electrical heating first increased oil recovery by up to 27% in seawater compared to 16% in deionised water. When Fe2O3 nanofluid was injected, oil recovery further increased to 32% in seawater and 24% in deionised water. The contact angle and zeta potential decreased from 124° to 36° and from −24.4 to −23.7 mV, respectively, when nanofluid was injected in seawater, leading to better nanofluid stability and penetration into the carbonate rock as shown by increased pellet porosity from 6.6% to 14.8%. Moreover, it was found that the interfacial tension was reduced from 72 to 32.7 mN/m in the pre-magnetised samples with Fe2O3 NPs injection compared to 33.2 mN/m in the samples with MgO injection. It was found from our experiments that the effect of the generated electricity on the surface charge was of a temporary nature as the zeta potential of the rock returned to its original value as soon as the power was disconnected. The mechanism underlying the hybrid Enhanced Oil Recovery EOR technique from the laboratory findings was found to be based on electrowetting and nanofluid adsorption. Results indicate that the technique is promising for further improving oil recovery and securing energy supply during the transition to net zero

A Comparative Study of Diffusion Coefficients from Convective and IR Drying of Woodchip

Convective and infared (IR) Halogen Drying processes are used in the woodchip biomass industry to test the moisture content of woodchip. Woodchip drying, though energy intensive, is necessary to increase the calorific content of woodchip, in turn increasing combustibility. The bulk process within the production of woodchip uses convective drying with agitation. Analysis of the diffusion in wood can be used to estimate the time to dry lumber to a specified moisture content value. Relationships between the effect of temperature and moisture content allow more accurate predictions and operational evaluations of driers. The aim of this study was to investigate constant heat source convective and IR drying by comparing the drying curves when batch drying a sample of woodchip biomass whilst controlling the heat source temperature at 328K, 338K, 348K and 358K. This was achieved through comparison of pre-exponential diffusion coefficients and activation energy, determining the temperature dependency of these terms in convective and IR drying of wetted wood. Lower temperatures increased drying time for both convective and IR drying, with convective drying taking up to 5 times longer than IR. The pre-exponential diffusion coefficient and activation energy found for IR drying were m2.s-1 and J.mol-1. The convective drying pre-exponential diffusion coefficient and activation energy calculated was m2.s-1 and J.mol-1 respectively

Mathematical Model Analysis for Mass and Rates of Woodchip IR Drying

The production of woodchip biomass, by meansofdrying, is of importancewith respect to environmental concerns. This has been highlighted by reports of carbon production through utility usage of commercial sites, where drying is often among the most energy intensive operations within industrial processes. It is therefore crucial to dry wood in efficient way in order to derive high quality products and increase end use process efficiency. Akey component for dry fuel suppliers is the moisture content of the woodchip product. Halogen (infrared) drying is the foremost method used on site to measure moisture content ofwood fuel for supply,as this takes less time,asmaller sample size and less human interaction, in comparison with convective drying. This study investigated the drying behaviour of static woodchip fuel using an infrared source at temperatures rangingfrom 50 to 80°C and atmospheric pressure. With the longest drying time (time until a rate of 0.001g per 99 seconds is reached) of just over three hours and the shortest under an hour and a half. Mathematical models of the drying rates were determined through statistical analysis and the significance of the initial drying periods relevant to rates of falling and constant profiles were analysed for the different temperatures. Statistically the model with the best fit at the temperatures measured was a diffusion model with 6 exponential terms and coefficients with the SSE value 0.2424, R2of 0.9989 and RMSE of less than0.009. Models with 4 coefficients were also able to fit the data well with SSE values of below 0.03. Differentiating the resulting equations of fit at constant temperature resulted in models for the rate of mass lost over time

Tuning the wettability of wire mesh column:pore-scale flow analysis

The pore-scale behaviour of liquid flow over wire mesh stainless-steel packing of variable contact angle is relevant for mass and heat exchanges in multiphase chemical systems. This behaviour was investigated by imaging experiments and 3D volume-of-fluid modelling. The surface of the wire mesh ring was modified by alumina coating to reach both hydrophilic and hydrophobic characteristics. The cycle of capillary droplet flow over the uncoated ring exhibited penetration of the hydrophilic mesh openings, adherence to the surface of the ring and accumulation as drips at the bottom region of the rings. However, over the hydrophobic ring, the droplet exhibited low adherence to the ring surface, accumulation at the top surface of the ring, no penetration of the openings, slip by the gravitational forces over the vertical curvature and accumulation as drips at the bottom region. In agreement with the classical observations at the macroscale, the observations at the pore-scale confirmed the increase of the wetting efficiency, liquid holdup and effective surface area at increased liquid flowrate and reduced contact angle. The 3D model was in reasonable agreement with Stichlmair's model for the liquid holdup, particularly in the hydrophilic zone of the contact angle and low flow as well as in a reasonable agreement with Linek's model for effective area, particularly in the hydrophobic range of the contact angle

Deactivation of the preferential oxidation of CO in packed bed reactor by 3D modelling and near-infrared tomography

Scaling up the results on catalyst deactivation to industrial operations, where transport phenomena are of significance, is often not straightforward. The operations of industrial reactors are judiciously focused on the dynamics of the deactivation along the axial length of the reactors, which are generally known approximately. Processes of strong energy release or fast chemical kinetics, such as oxidation reactions, cracking, etc., are associated with a deactivation where the time characteristics of the flow and transports are of magnitudes of the deactivation time-on-stream. Local deactivation of the preferential oxidation of CO was investigated by three-dimensional modelling of flow, mass and heat transfers inside a packed-bed reactor and validated by near-infrared tomography. The profiles of deactivation were sensitive to the rates of deactivation, heat transfer by dispersion and intra-particle mass transfer. At pore scale of the packing, pronounced deactivation was revealed near the wall due to a preferential flow circulation. The deactivation progressed at the exteriors of the catalytic particles, particularly over the regions in contact with the convective flow. Unlike the mass dispersion, the heat dispersion promoted the deactivation by shifting the moving waves of deactivation upstream, leading to asymmetrical maps inside the catalytic particles