Metal phosphates, insoluble

In the double-neutralization process, Na2SiFg is precipitated and removed by filtration at a pH of 3—4 (9). Upon raising the pH to 7—9, insoluble phosphates of Fe, Al, Ca, and Mg form and separate. Iron can be precipitated as hydrous ferric oxide, reducing the phosphate loss at the second filter cake. Both the fluorosihcate and metal phosphate filter residues tend to be voluminous cakes that shrink when dewatered recovery of soluble phosphates trapped within the cakes is difficult. 

Multilayers of Diphosphates. One way to find surface reactions that may lead to the formation of SAMs is to look for reactions that result in an insoluble salt. This is the case for phosphate monolayers, based on their highly insoluble salts with tetravalent transition metal ions. In these salts, the phosphates form layer stmctures, one OH group sticking to either side. Thus, replacing the OH with an alkyl chain to form the alkyl phosphonic acid was expected to result in a bilayer stmcture with alkyl chains extending from both sides of the metal phosphate sheet (335). When zirconium (TV) is used the distance between next neighbor alkyl chains is - 0.53 nm, which forces either chain disorder or chain tilt so that VDW attractive interactions can be reestablished. 

Lithium orthophosphates are unimportant and differ from the other alkali metal phosphates in being insoluble. At least 10 crystalline hydrated or anhydrous sodium orthophosphates are known and these can be grouped into three series ... 

Most trace metals may be precipitated with phosphate into insoluble metal phosphates (Table 7.5). Most metal phosphates have low solubility. High localization of phosphates reduces the bioavailability of Zn in arid soils. The banded application of P near the seeds depresses Zn uptake by com (Adriano and Murphy, 1970 Grant and Bailey, 1993), causing Zn deficiency. However, both N and P fertilizers increase Cd concentration in plants. Cadmium and Zn are antagonistic in root uptake and distribution within plants. 

Phosphate removal processes from wastewater have been studied by many workers, in order to protect stagnant water area, such as lakes and coastal region from eutrophication. Among conventional phosphate removal processes, the representative one was flocculation and sedimentation process, which was based on precipitation of insoluble metal phosphate or hydroxide. However, the main problem with this process, is to produce large amounts of sludge, which is difficult to dehydrate. 

In aqueous media lutetium occurs as tripositive Lu3+ ion. All its compounds are in +3 valence state. Aqueous solutions of all its salts are colorless, while in dry form they are white crystalline solids. The soluble salts such as chloride, bromide, iodide, nitrate, sulfate and acetate form hydrates upon crystallization. The oxide, hydroxide, fluoride, carbonate, phosphate, and oxalate of the metal are insoluble in water. The metal dissolves in acids forming the corresponding salts upon evaporation of the solution and crystallization. 

STABCAL was also used to construct pE-pH stability fields for chloropyromorphite, hinsdalite, plumbogummite, tricadmium diphosphate, tricopper diphosphate, and hopeite (Fig. 7). These diagrams allow for estimation of stability with respect to pH and to the presence of insoluble sulphides. The NBS thermodynamic database (Wagman et al. 1982) was used as a source of thermodynamic data. The total concentrations chosen for each metal were selected to produce a stability region for the metal phosphate solid. In some cases, this was a very low total concentration (e.g., CTPb =1 x 10 10 M for Pb). In other cases, the total metals concentration was high (e.g., C r.cd— 1 x 10 3 M for Cd). The modelling exercise used typical equilibrium concentrations for MSW bottom ash leachates as shown in Table 2. 

A further development in the 1980s/1990s was the introduction of some newer catalysts. Narrow range or peaked ethoxylates can be made using acid activated metal alkoxides, metal phosphates or activated metal oxides as catalyst. These catalysts are insoluble and therefore heterogeneous in nature and the major process difference is that catalyst slurry is added to the reactor after which the conditions are exactly as with normal alkaline catalysts. The reactions are slightly quicker and need less catalyst but it must be filtered out. Most producers [ 12-20 ] have patents on these systems, the advantages of which are seen in the finished products as ... 

Orthophosphates.—Solubility.—The tribasic phosphates of the alkali metals and ammonia are soluble, while those of the alkaline earth metals and the common metals are insoluble. They are usually prepared by double decomposition between disodium hydrogen phosphate and a salt of the required metal, thus... 

C. vulgatum occur in the digestive gland, where they are accumulated within intracellular phosphate granules and residual lyso-somes. The metals are unavailable to the animal in the sense that they are insoluble and within membrane-limited compartments at high concentration. When the digestive glands are consumed by the carnivore, the metals remain insoluble and unavailable in the gut, so that the detoxifica-... 

The Ciroup I earixmates and suUates are very soluble, but those of Group 2 arc mainly in the sparingly soluble insoluble classes apart from the quite soluble Be and Mg sulfales. The Group 2 haliilcs are till very soluble except for the lluorides their - 2 ions are leltiiively small and solubility is favoured by the throe larger halide ions. The phosphates of sodium and potassium arc quite soluble, but those of the Grotip 2 metals tire insoluble, as is aluminium phospliale. 

Group 4. Insoluble phosphates At this point the solution contains only metal ions from groups lA and 2A of the periodic table. Adding (NH4)2HP04 to a basic solution precipitates the group 2A elements Mg, Ca, Sr ", and Ba " because these metals form insoluble phosphates. 

Attack on the metal may in some cases involve the formation of acid-resistant films of insoluble metal phosphates (e.g. Fe, Zn, Mn) and perhaps metal oxides. 

Present processes are variously referred to as phosphating, phosphorising or phosphatising, and all involve the formation of relatively insoluble, electrically non-conducting thin films of metallic phosphates on the surface of the metal being treated. A very large and continually growing number of patents now exist in this field. 

Iron is readily attacked by orthophosphoric acid over a wide range of temperature and concentration. This attack involves the initial formation of sparingly soluble dihydrogen phosphate (12.32). As the pH rises in the vicinity of the metal snrface, insoluble monohydrogen phosphate is precipitated (12.33), and eventually tribasic iron phosphate may also form (12.34). 

Although phosphorus is the eleventh most abundant element in the Earth s crust, where it forms approximately 1120 mg kg , it is geochemically classed as a trace element [1,2]. In the lithosphere, it occurs as phosphates, and these may be leached by weathering processes into the hydrosphere. Phosphorus may then be precipitated as insoluble metal phosphates, which are incorporated into sediments and cycled on a geological timescale (millions of years), or it can participate in the rapid terrestrial and aquatic biological phosphorus cycles. 

An important distinction between phosphoric acid activation (to produce a carbon) and the chemical modification of wood by phosphoric acid (fire retardants) is that, in the former case (the commercial case), phosphoric acid is removed after reaction by leaching to recover the reagent and heat treatment is then continued. For this reason, the phosphorous content of the recovered carbons only indicates the amount of residual material that is present, either combined with the organic structure, in the form of insoluble metal phosphates, or physically entrapped. 

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