Abstract The present study investigated the dynamics of manganese adsorption onto bone char in a continuous fixed bed column using a mathematical model that incorporates: (i) the backmixing model to describe the fluid flow through the bed and (ii) the shrinking core model to describe the kinetic and mass transfer phenomena within spherical adsorbent particles. The proposed model consists of an ordinary differential equation system. Hydrodynamic, kinetic and diffusive parameters were determined by fitting the mathematical model to the experimental data obtained by Sicupira et al. (2015). For the operating conditions evaluated in this study, the intraparticle diffusion represented the controlling step of the adsorption process (Bim> 3.8). The increase in the feed rate of the column (3.0-7.5 mL min-1) and the decrease in the height of the bed (8-16 cm) resulted in a decrease in the time required for the saturation of the column bed. The model is flexible for a variety of flow conditions and adequately reproduced the behavior of the manganese adsorption process in the fixed bed column operation (R²> 0.99) with an average percentage error less than15%.

Abstract The present study investigated the solvent extraction of uranium from sulfate acid solutions using Alamine 336 as an extractant dissolved in commercial kerosene Exxsol D-100 and 5% v/v of tridecanol as a modifying agent at room temperature (25±2) ºC and an aqueous/organic volumetric ratio of unity. Experiments were carried out at typical concentration levels like those used at the uranium plant of INB (Indústrias Nucleares do Brasil), Brazil. Data fitting using the slope analysis method revealed that uranium is extracted by Alamine 336 as UO2SO4 and UO2(SO4)22- species, forming (R3NH+)2UO2(SO4)22- in the organic phase; the extraction of the species UO2(SO4)34- seems improbable for the operating conditions investigated. The extraction of uranium is significantly reduced when the concentrations of sulfate and chloride ions in the aqueous phase are increased.

Abstract The present study investigated the dynamics of batch adsorption of manganese onto bone char by using two distinct mathematical formulations: the diffusion model and the shrinking core model. Both models assumed spherical particles and adequately described the transient behavior of metal adsorption under changing operating conditions. Comparatively, the diffusion model described the manganese adsorption better at distinct particle sizes even when small particles were used (dp ≤ 0.147 mm); the shrinking core model proved to be more reliable when larger adsorbent particles were used (dp > 0.147 mm), and it described experimental data better at changing solid-liquid ratios. Manganese adsorption was favored when: (i) smaller adsorbing particles were used due to the increase in the contact area and easier access to reacting sites of the char; however, such an effect proved to be limited to dp ≤ 0.147 mm, and (ii) higher solid-liquid ratios were used due to the increase in the available reacting sites. External and intraparticle mass transfer dependences on particle size and solid-liquid ratio were also investigated, and results corroborated with prior investigations found in the literature.

AbstractIn the present study, continuous fixed bed column runs were carried out in an attempt to evaluate the feasibility of using bone char for the removal of manganese from acid mine drainage (AMD). Tests using a laboratory solution of pure manganese at typical concentration levels were also performed for comparison purposes. The following operating variables were evaluated: column height, flow rate, and initial pH. Significant variations in resistance to the mass transfer of manganese into the bone char were identified using the Thomas model. A significant effect of the bed height could only be observed in tests using the laboratory solution. No significant change in the breakthrough volume could be observed with different flow rates. By increasing the initial pH from 2.96 to 5.50, the breakthrough volume was also increased. The maximum manganese loading capacity in continuous tests using bone char for AMD effluents was 6.03 mg g-1, as compared to 26.74 mg g-1 when using the laboratory solution. The present study also performed desorption tests, using solutions of HCl, H2SO4, and water, aimed at the reuse of the adsorbent; however, no promising results were obtained due to low desorption levels associated with a relatively high mass loss. Despite the desorption results, the removal of manganese from AMD effluents using bone char as an adsorbent is technically feasible and attends to environmental legislation. It is interesting to note that the use of bone char for manganese removal may avoid the need for pH corrections of effluents after treatment. Moreover, bone char can also serve to remove fluoride ions and other metals, thus representing an interesting alternative material for the treatment of AMD effluents.

The present study investigated batch kinetics and the batch equilibrium of manganese removal from acid mine drainage (AMD) using bone char as an adsorbent. Equilibrium tests revealed that the Langmuir-based maximum manganese uptake capacity was 22 mg g-1 for AMD effluents and 20 mg g-1 for laboratory solutions at a pH ranging from 5.5 to 5.7. The pseudo-second order model best described the manganese kinetics within bone char. Manganese removal was mainly influenced by the operating variables of the solid/liquid ratio and the pH of the aqueous phase. In fact, metal uptake was favored at nearly neutral pH values. The effect of particle size and temperature proved to be insignificant for the investigated operating range. This work also evaluated the mechanism for manganese removal using bone char. Results showed that intraparticle diffusion is the main rate-limiting step; however, additional contributions from boundary layer diffusion may well affect this removal when particles of smaller sizes are used. The final concentration of fluoride and other metals present in the AMD effluent was in agreement with the concentration limit set forth by Brazilian legislation. The present study demonstrated that bone char is a suitable material to be used for the removal of manganese from AMD effluents.

A model is proposed in this paper to describe the generation of acid mine drainage (AMD) in leaching columns. The model considers: (i) Water flow through the column, which is calculated using the 1 - D analytic solution of the Richards' equation assuming the existence of a similarity relationship between the water retention function and the water content profiles at a given time; and (ii) Pyrite oxidation weighted by microbiological effects occurring in spherical particles according to the shrinking core model. Mass balances of oxygen and pyrite were derived in order to evaluate the intrinsic oxidation rate and the pyrite fraction reacted with time and column position. The model was used to simulate a six month operation of a leaching column, which comprised successive weekly cycles of dry and wet periods. Simulation results demonstrated that AMD generation is strongly affected by the presence of microorganisms. A relative deviation of 5% between simulation and experimental data was obtained.