Coated particles hydrous oxide

Adsorption of Metal Ions and Ligands. The sohd—solution interface is of greatest importance in regulating the concentration of aquatic solutes and pollutants. Suspended inorganic and organic particles and biomass, sediments, soils, and minerals, eg, in aquifers and infiltration systems, act as adsorbents. The reactions occurring at interfaces can be described with the help of surface-chemical theories (surface complex formation) (25). The adsorption of polar substances, eg, metal cations, M, anions. A, and weak acids, HA, on hydrous oxide, clay, or organically coated surfaces may be described in terms of surface-coordination reactions ... 

If a surface precipitate of metal hydroxy-polymer has formed on an adsorbent, the -pH relationship for the coated adsorbent should resemble closely that observed for particles consisting purely of the hydroxy-polymer or the hydrous oxide of the metal (15). This kind of evidence for Co(ll), La(lII), and Th(lV) precipitation on silica colloids was cited by James and Healy (15). It should be noted, however, that the increase in C toward a maximum value often occurs at pH values well below that required thermodynamically to induce bulk-solution homogeneous precipitation of a metal hydrous oxide (15, 16). If surface precipitation is in the incipient stage under these conditions, it must be a nucleation phenomenon. James and Healy (15) argue that the microscopic electric field at the surface of a charged adsorbent is sufficiently strong to lower the vicinal water activity and induce precipitation at pH values below that required for bulk-solution precipitation of a metal hydrous oxide. 

Gardner, W.K. Parbery, D.G. Barber, D.A. (1982) The acquisition of phosphorus by Lu-pinus albus L. I. Some characteristics of the soil/root interface. Plant Soil 68 19-32 Garg, A. Matijevic, E. (1988) Preparation and properties of uniform coated colloidal particles. II. Chromium hydrous oxide on hematite. Langmuir 4 38-44 Garg, A. Matijevic, E. (1988) Preparation and properties of uniform coated colloidal parti-... 

Figure 1.1.20 shows the differential thermal analysis (DTA) data for the cores, of chromium hydrous oxides particles prepared in the absence of hematite, and of coated particles. It is obvious that the latter behave as the coating material, when alone. This example clearly indicates the possibility of having the surface site characteristics of chromium hydrous oxide induced onto ellipsoidal iron oxide particles. The latter morphology cannot be achieved by diiecl precipitation of the same chromium compound. 

Analogously, hematite particles could be coated with zirconium hydrous oxide by aging zirconium sulfate solutions in the presence of cores, which required the... 

Fig. 1.1.19 (A) TEM of ellipsoidal hematite (a-Fci03) particles and (B) of the same particles coated by chromium hydrous oxide obtained by aging at 85°C for 6 h 40 cm3 of a dispersion containing 30 mg dm-3 of the cores in the presence of 5.0 X 10-4 mol dm-3 chrome alum. (From Ref. 144.)...

Fig. 1.1.20 Differential thermal analysis data for chromium hydrous oxide, hematite, and hematite particles coated with chromium hydrous oxide. Data refer to dispersions as illustrated in Fig. 1.1.19.

Finally, rod-like particles of indium hydrous oxide, dispersed in solutions of HfOCl2 and Na2S04, were coated with hafnium hydrous oxide by simply aging the entire system for 24 h at room temperature (149). 

Hydrous Oxides. This term is generally taken to include the oxides, hydroxides, and oxyhydroxides of aluminium, iron and manganese, which form in soil when these elements are released from primary minerals by weathering. They exist mainly as small particles in the claysized fraction of a soil (<2 pm), and also as coatings on other soil minerals or as components of larger aggregates. 

Finally, finely divided hydrous oxides of iron, aluminum, manganese, and silicon are the dominant sorbents in nature because they are common in soils and rivers, where they tend to coat other particles. This is the reason why numerous laboratory researchers have been studying the uptake of trace elements by adsorption on hydrous oxides (Dzomback and Morel, 1990). Partition coefficients (concentration in solid/concentration in the solution) for a number of trace elements and a great variety of surfaces have been determined. The comparison of these experimental with natural values should give information on the nature of the material on which trace elements adsorb in namral systems and allow quantitative modeling. 

Garg, A. and Matijevic, E. (1988) Preparation and properties of coated uniform colloidal particles. II. Chromium hydrous oxide on hematite. Langmuir 4 38-44. 

Dobrikova, A.G. et al.. Protein-coated p icrric hydrous oxide particles. An electrokinetic and electrooptic study, Colloids Surf. B. 56, 114, 2007. 

Over the decades that have passed since La Mer s work numerous examples of monodispersed particles of various composition, morphologies and properties, as well as methods for their preparation (not limited to condensational formation), were described in the literature. Extensive studies in this area were carried out by E. Matijevic and T. Sugimoto. Examples of monodisperse systems formed by precipitation from homogeneous solutions include dispersions of uniform particles of simple composition having different morphologies, such as metal halides, sulfides, phosphates, (hydrous) oxides, etc, various composite particles, including particles of internally mixed composition and coated particles. Both crystalline and amorphous materials can be obtained. Electron micrographs of some characteristic examples of monodispersed colloids are shown in Fig. IV-14. 

Garg A, Matijevic E (1988) Preparation and properties of uniformly coated inorganic colloidal particles, 3. Zirconium hydrous oxide on hematite. J Colloid Interface Sci 126 243-250... 

Kratohvil S, Matijevic E (1987) Prepration and properties of coated, uniform, inorganic colloidal particles, 1. Aluminum (hydrous) oxide on hematite, chromia and titania. Adv Ceram Mater 2 798-803... 

Polymeric coatings of soil particles by humus, by hydrous iron(III) oxides and hydroxo-AI(III) compounds... 

Adsorption of mercury. All chemicals used were Merck or Baker analytical quality reagents, unless stated otherwise. From the commercially available adsorbents the following were used silica gel 60 A porosity, 0.063-0.200 mm particle size (Merck) charcoal 0.3-0.5 mm particle size, gas-chromatographic quality (Merck) alumina R Woelm hydrous zirconium oxide HZ0-1, 100-200 mesh, (Bio-Rad). Except for zirconium phosphate, which was prepared according to Amphlett ( ), all other sorbents were prepared by coating (precipitation) on acid-purified silica gel, as described in (1 ). The Si0 -NH was prepared according to Leyden et al (11). L... 

Sorption of arsenic to hydrous metal oxide phases (usually found as coatings on other mineral phases, or as clay-to-colloidal-sized particles) is an... 

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