Systems inorganic precipitation

Ripening can change the particle size distribution of a precipitate over a period of time, even in an isothermal system, but the change can be accelerated by the use of controlled temperature fluctuations. This process, known as temperature cycling , has been utilized to alter the physical characteristics of organic and inorganic precipitates (Carless and Foster, 1966 Nyvlt, 1973 Brown, Marquering and Myerson, 1990). 

Fouling is typically associated with microfiltration and ultrafiltration due to the employment of porous membranes combined with the characteristics of the feed solution. In the case of e.g. reverse osmosis where low molecular solutes such as salts are retained the fouling tendency is low. But foulants such as organic and inorganic precipitates and suspended solids may be present as well. Since in these systems often hollow fiber and spiral wound configurations are applied fouling may occur in the feed channels since these configurations are very susceptible and measures have to be taken and this will be described in the next section. 

Using the aforementioned methods, retrievable nanoreactors (as shown in Fig. 15.1) can be prepared at relatively high concentrations (> 10 particles per mL), but due to the nature of ionic condensation of calcium and phosphate, the system is significantly diluted prior to coating in order to avoid end products with multiple perfluorocarbon cores fused together, or the formation of solid inorganic precipitates. 

A fourth mechanism is called sweep flocculation. It is used primarily in very low soflds systems such as raw water clarification. Addition of an inorganic salt produces a metal hydroxide precipitate which entrains fine particles of other suspended soflds as it settles. A variation of this mechanism is sometimes employed for suspensions that do not respond to polymeric flocculants. A soHd material such as clay is deUberately added to the suspension and then flocculated with a high molecular weight polymer. The original suspended matter is entrained in the clay floes formed by the bridging mechanism and is removed with the clay. 

Inorganic reactions in the soil interstitial waters also influence dissolved P concentrations. These reactions include the dissolution or precipitation of P-containing minerals or the adsorption and desorption of P onto and from mineral surfaces. As discussed above, the inorganic reactivity of phosphate is strongly dependent on pH. In alkaline systems, apatite solubility should limit groundwater phosphate whereas in acidic soils, aluminum phosphates should dominate. Adsorption of phosphate onto mineral surfaces, such as iron or aluminum oxyhydroxides and clays, is favored by low solution pH and may influence soil interstitial water concentrations. Phosphorus will be exchanged between organic materials, soil inter-... 

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