Granular ferric hydroxide (GFH) is often used for fixed bed adsorbent (FBA) columns in groundwater purification units around the world to remove arsenate contaminations. Groundwater can contain also other toxic (e.g., antimonite and vanadate) and non-toxic oxo-anions (phosphate and silicic acid) that are known to affect FBA lifetimes. Therefore, understanding the breakthrough of toxic compounds intended for removal by FBA is essential to their design, and is important to predict accurately breakthrough curves (BTCs) for FBAs in waterworks to plan future operating costs. Rapid small-scale column tests (RSCCT) and pilot-scale FBA were used to simulate vanadate BTCs for complex groundwater chemistries. The BTCs were simulated successfully using a homogeneous surface diffusion model (HSDM) combining equilibrium chemical adsorption and kinetic mass transfer. Adsorption parameters for various groundwater compositions were predicted using the CD-MUSIC surface complexation model, which was set up for the first time for akaganéite-based granular ferric hydroxide with a competitive multi-solute system. The results indicated that V(V) is less prone to competitive adsorption effects, and use of the homogeneous surface diffusion model to predict the BTCs requires then the kinetic mass transfer Biot number to be used as the only fitting parameter. On the other hand, a concentration overshoot could be observed for the two weaker absorbed oxo-anions arsenate and phosphate because of displacement by the vanadate. Results of pilot scale test column BTCs of vanadate for three waterworks with different groundwater compositions could be favorably extrapolated with a unique Freundlich constant k F of 3.2 derived on basis of the multi-solute CD-MUSIC model, and a unique Biot number of 37 fixed for all three different test sites.
Highly porous, fired ceramic concretes, which are heterogeneous, polyfractionated compositions based on coarse porous refractory fillers and dispersed ceramic bond (cement) [i], are of interest in developing refractory, heat-insulating materials (in particular, in the production of large articles for lining furnaces). The authors of [2] present certain data on the production of specimens of zircon ceramic conc=ete with a total porosity of up to 70%. However, in contrast to dense ceramic concretes, the production method and properties of which have been studied in detail [i, 3, 4], special studies into the highly porous ceramic concretes have not been carried out, although data exist on the effective use of such materials [5].High porous ceramic concretes, compared with other highly porous materials (for example, foamed ceramics [2,6,7]), have some technical advantages (much lower water requirements for the molding system, and a reduction in shrinkage at the drying and firing stages), as well as improved exploitation properties, for example, thermal-shock resistance and volume stabi-This article, using ceramic concretes made of zirconia as an example, examines some general problems in obtaining highly porous ceramic concretes, and studies the effect of some technological factors on the material's properties.The original material consisted of highly dispersed (80% particles measuring not more than 5 ~m, maximum size i0 ~m) zirconia, stabilized with yttrium oxide and obtained by chemical precipitation from salt solutions [8]. The suspension (bond for ceramic concrete) was obtained by suspension in HCl-acidified water with a suspension pH of 2.0-2.5. The suspensions were subjected to mechanical mixing to deflocculate them, the effect of which for Zr02 was established previously [9]. This resulted in the removal of entrapped air. In view of the increased dispersion of the particles of solid phase, and the relatively low value of the ionic potential, determining the hydration capacity [ID], the Zr0= bond, after completion of the structure formation, possesses an enhanced (up to 3-4%) shrinkage during drying which, according to [i], complicates the technology for ceramic concretes in view of the creation of shrinkage tensions in the system. The highly porous (80-85%) filler was obtained by crushing briquets [Ii] sintered at 1580~ made of zircon foamed ceramics. In this case, the crushing product yielded both coarse (3-15 mm) and fine (0.06-0.63 mm) fractions of filler. It should be mentioned that with a reduction in the filler particle size, its actual porosity compared with that of the briquet was reduced as a result of the reduction in volume concentration in the grains of the coarse (0.1-0.4 mm) spherical pores. Moreover, while for grains measuring 5-10 mm (optimum size of coarse fraction) the porosity was about 80%, then for grains measuring 0.1-0.4 mm (optimum size of fine fraction) it was reduced to 30-35%. In accordance with this the porosity of the ceramic concrete to a large degree is determined by the volume ...
A. A. Dabizha and S. Yuo Pliner UDC 666~762.5o001~5Realizing the advantages of ceramics compared with metal alloys at high temperatures and in corrosive media is difficult because of their brittleness, which is due to defects in the microstructure, the ionic-covalent nature of the chemical bond, and the low mobility of the dislocations [1-3], The destruction of ceramic materials takes place in the region of low elastic deformations as a result of the catastrophic distribution of cracks already in existence, when the mechanical and thermal stresses exceed a certain critical magnitude [4]~ Numerous researchers have established that at the present time the most promising materials to obtain a high resistance to failure are those containing finely dispersed particles of ZrOa in the ceramic matrix [5]. To explain the effect of increasing the impact strength and other strengths of such materials two mechanisms are suggested: the first is based on the mechanism of the absorption of energy during the phase inversion of tetragonal particles of ZrO2 around a sharply developing crack [6,7]; the second is linked with the development and distribution of microcracks in the matrix, which is a result of a phase inversion of particles of ZrO2 during cooling of the fired specimens and the absorption of energy during the spreading of the bifurcating cracks [5,8]. Apparently, it is most probable that these two mechanisms operate simultaneously.
It was established that the relative length (size) of the zone of columnar grains can be used as a qualitative criterion for eva]uatJng the degree of chemical segregation along the cross section of the ingots obtained by continuous induction melting.Consequently, it was possible to find wider application of induction melting.The applications include the possibility of studying the composition vs property diagrams of the high-temperature engineering systems.Based on the theory of directional solidification and zone refining as applied to the technology of continuous IMCC process, we obtained the numerical values of the diffusion coefficient of the aluminum and chromium oxides and the impurities in molten magnesium oxide.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.