The sequestral capture of fluoride,nitrate and phosphate by metal-doped and surfactant-modified hybrid clay materials

Toxic anions removal for increased access to potable water remains a problem that has not been adequately addressed. This study, reports the successful preparation and modification of kaolinite-papaya seed based adsorbents under vacuum (VHYCA) for the removal of Nitrate (NO₃ ^?), Fluoride (F^?) and Phosphate (PO₄ ^3?). Modified adsorbents via metal-doping using Zinc were more efficient in removing these anions from aqueous solution compared with surfactant-modified adsorbents. However, both type of adsorbents showed a higher preference for NO₃ ^? removal with Zn-VHYCA and Fe-VHYCA adsorbents having 98 and 85% removal of the anion from aqueous solution, respectively. The removal of F^? and PO₄ ^3? was best achieved by Ortho-phenylenediamine (OP) and N,N,N′,N′-Tetramethyl-1,4-phenyldiaminedihydrochloride (TPD) modified VHYCA, respectively. However, Zn-VHYCA adsorbent showed comparable results with TPD-VHYCA in the removal of PO₄ ^3? from aqueous solution. Overall, the metal-doped hybrid clay adsorbents showed better efficiency for the removal of anions than the surfactant-modified hybrid clay adsorbents.     

Galerkin finite element simulation of convection driven by rotation and gravitation

The performance of the Galerkin finite element method when applied to time-dependent convection involving rotation, self-gravitation and the normal gravity field in a horizontal cylinder is discussed in this paper. The governing equations, the parameters of the problem and our implementation of the numerical schemes are presented. The accuracy, spatial scale of resolution, flexibility and robustness of the resulting code show the element method as a valuable tool for research in this area or in related problems in astrophysical fluid dynamics. The numerical difficulties in large-amplitude flows are associated with an error-control scheme for time integration and the ‘short-time’ wiggles in transient Dirichlet problems. Coarse grids give the correct qualitative picture in most simulations, but the type of solution at short time (and hence grid refinement) presumably resolves the degeneracy in the azimuthal orientation of convection cells in flows driven by self-gravitation and (perhaps) centrifugal buoyancy. The final state in transient flows is a motionless isothermal fluid. However, residual motions can be nullified only in the limit of zero grid size in flows driven by centrifugal buoyancy (self-gravitation), while a fairly coarse grid is sufficient for this purpose in normal gravity-driven flows.     

Calculation of Reynolds stresses in turbulent supersonic flows

The baseline numerical procedure of interest in this study combines flux vector splitting, flux difference splitting and an explicit treatment of the diffusion terms of the flow equations. The viscous terms are treated explicitly to preserve the wave propagation properties of the Euler fluxes and permit splitting. The experience with this scheme has been limited to laminar or, at best, ‘eddy viscosity’ flows. In this paper the applicability of the scheme is extended to include the calculation of turbulent Reynolds stresses in supersonic flows. The schemes and our implementation are discussed. Both laminar and turbulence subsets of the Reynolds/Favre-averaged equations are tested, with a discussion of relative performance. The test problem for turbulence consists of a zero-pressure-gradient supersonic boundary layer as well as a supersonic boundary layer experiencing the combined effects of adverse pressure gradient, bulk compression and a concave streamline curvature. Excellent agreement with experimental measurements is observed for most of the quantities compared, which suggests that the numerical procedures presented in this paper are potentially very useful.