Phosphate arsenate

Thousands of compounds of the actinide elements have been prepared, and the properties of some of the important binary compounds are summarized in Table 8 (13,17,18,22). The binary compounds with carbon, boron, nitrogen, siUcon, and sulfur are not included these are of interest, however, because of their stabiUty at high temperatures. A large number of ternary compounds, including numerous oxyhaUdes, and more compHcated compounds have been synthesized and characterized. These include many intermediate (nonstoichiometric) oxides, and besides the nitrates, sulfates, peroxides, and carbonates, compounds such as phosphates, arsenates, cyanides, cyanates, thiocyanates, selenocyanates, sulfites, selenates, selenites, teUurates, tellurites, selenides, and teUurides. 

Fluoride < chloride < bromide = iodide = acetate < molybdate < phosphate < arsenate < nitrate < tartrate < citrate < chromate < sulfate < hydroxide. 

Heating with the following solids, their fusions, or vapours (a) oxides, peroxides, hydroxides, nitrates, nitrites, sulphides, cyanides, hexacyano-ferrate(III), and hexacyanoferrate(II) of the alkali and alkaline-earth metals (except oxides and hydroxides of calcium and strontium) (b) molten lead, silver, copper, zinc, bismuth, tin, or gold, or mixtures which form these metals upon reduction (c) phosphorus, arsenic, antimony, or silicon, or mixtures which form these elements upon reduction, particularly phosphates, arsenates,... 

The method may be applied to those anions (e.g. chloride, bromide, and iodide) which are completely precipitated by silver and are sparingly soluble in dilute nitric acid. Excess of standard silver nitrate solution is added to the solution containing free nitric acid, and the residual silver nitrate solution is titrated with standard thiocyanate solution. This is sometimes termed the residual process. Anions whose silver salts are slightly soluble in water, but which are soluble in nitric acid, such as phosphate, arsenate, chromate, sulphide, and oxalate, may be precipitated in neutral solution with an excess of standard silver nitrate solution. The precipitate is filtered off, thoroughly washed, dissolved in dilute nitric acid, and the silver titrated with thiocyanate solution. Alternatively, the residual silver nitrate in the filtrate from the precipitation may be determined with thiocyanate solution after acidification with dilute nitric acid. 

Phosphate, arsenate, and vanadate interfere. Borate, fluoride, and large amounts of aluminium, calcium, magnesium, and the alkali metals have no effect in the determination, but large amounts of iron (> 5 per cent) appear to produce slightly low results. 

Sulphuric acid is not recommended, because sulphate ions have a certain tendency to form complexes with iron(III) ions. Silver, copper, nickel, cobalt, titanium, uranium, molybdenum, mercury (>lgL-1), zinc, cadmium, and bismuth interfere. Mercury(I) and tin(II) salts, if present, should be converted into the mercury(II) and tin(IV) salts, otherwise the colour is destroyed. Phosphates, arsenates, fluorides, oxalates, and tartrates interfere, since they form fairly stable complexes with iron(III) ions the influence of phosphates and arsenates is reduced by the presence of a comparatively high concentration of acid. 

B) Inorganic mixture containing Cd, Zn, Cu, Mg, phosphate, arsenate, borate... 

O Reilly et al. (2001) studied the effect of sorption residence time on arsenate desorption by phosphate (phosphate/arsenate molar ratio of 3) from goethite at different pH values. Initially, desorption was very fast (35% arsenate desorbed at pH 6.0 within 24 hrs) and then slowed down. Total desorption increased with time reaching about 65% total desorption after 5 months. These authors found no measurable effect of aging on desorption of arsenate in the presence of phosphate. Furthermore, desorption results at pH 4.0 were similar to the desorption behaviour at pH 6.0. On the contrary, Arai and Sparks (2002) demonstrated that the longer the residence time (3 days-1 year), the greater was the decrease in arsenate desorption by phosphate from a bayerite. 

The desorption of arsenate previously sorbed onto Fe- or Al-oxides or onto an Andisol containing 42% of allophanic materials (Vacca et al. 2002) by phosphate has been demonstrated to be affected by time of reaction, residence time of arsenate onto the surfaces and the pH of the system (Pigna et al. 2006 Pigna et al. 2007, unpublished data). Figure 9 shows the desorption of arsenate at pH 6.0 (phosphate/arsenate molar ratio of 4) when phosphate was added onto the soil (Andisol) sample 1, 5 or 15 days after arsenate (surface coverage of arsenate about 60%). After 60 days of reaction, 55% of arsenate was desorbed by phosphate when the residence time of arsenate onto the surfaces of the Andisol was 1 day, but 35 and 20% of arsenate was desorbed by phosphate with increase in the residence time up to 5 and 15 days. Further, it was also observed that by keeping the... 

Fig. 9. Desorption of arsenate (As04) from Andisol at pH 6.0 (phosphate/arsenate molar ratio of 4) when phosphate (P04) was added 1, 5 or 15 days after arsenate. Surface coverage of arsenate was about 60% (authors unpublished data, 2007).

Spectrophotometric Methods, Phosphate, Arsenate, Arsenite, and Sulfide... 

Johnson and Pilson [229] have described a spectrophotometric molybdenum blue method for the determination of phosphate, arsenate, and arsenite in estuary water and sea water. A reducing reagent is used to lower the oxidation state of any arsenic present to +3, which eliminates any absorbance caused by molybdoarsenate, since arsenite will not form the molybdenum complex. This results in an absorbance value for phosphate only. 

The oxalate method also provides information about the capacity of soils to adsorb certain compounds such as phosphate, arsenate etc. and to supply Fe to the plant root because both are influenced by their ferrihydrite content. In fact, a negative correlation was found between Fe, and the severity of chlorosis of sorghum in calcareous soils of Texas (Loeppert Hallmark, 1985) and FCo has been used for the sandy soils of the Netherlands to predict their capacity to adsorb phosphate and prevent P... 

As in pure systems, the adsorption of anions and cations on iron oxides is strongly pH dependent. This has to be kept in mind when an optimum pH is to be obtained with liming. The adsorption of phosphate, arsenate etc. increases as the pH falls below 7, whereas the adsorption of heavy metal cations rises as pH goes up (see eq. 11.18 11.19). Therefore, as soils become more acidic, heavy metals will be released into the soil solution. Conversely, liming soils has the opposite effect. 

Under acid conditions, molybdate reacts with orthophosphate, P04 to form a blue heteropoly acid, molybdophosphoric acid. A similar reaction occurs with arsenate ion, As04. In the presence of vanadium, the product is yellow vanadomolybdophosphoric acid. These reactions are used for colorimetric analyses of phosphate, arsenate, and many other substances. Colloidal molybdenum blue has limited apphcations such as dyeing silk. It readily absorbs onto surface-active materials. 

Phosphates, Arsenates, and Heavy Metals.— The tests me. to be carried out as detailed under Magnesium Chloride. 

A repressible acid phosphatase of Saccharomyces mellis develops when the organism is grown in a medium free of phosphate. Only traces of enzymic activity are found when media containing inorganic phosphate are used. The enzyme is inhibited by phosphate, arsenate, molybdate, and borate (117). 

Lactate, glycolate, succinate, chloride, malate, sulphate, tartrate, maleate, fluoride, a-hydroxybutyrate, hydroxy valerate, formate, valerate, pyruvate, monochloroacetate, bromate, galaconurate, nitrite, gluconurate, dichloroacetate, trifluoroacetate, hypophosphite, selenite, bromide, nitrate, oxalate, selenate, a-ketoglutarote, fumarate, phthalate, oxalacetate, phosphate, arsenate, chromate, citrate, isocitrate, cis aconitate and transaconitrate... 

Phosphates, arsenates, and vanadates contain a simple molecule of oxygen combined with phosphorous, arsenic, or vanadium. Compounds of P04 are most common. Although this is the largest group of non-silicate minerals, only a few of them are found in museums outside of mineral collections. The most notable exception is turquoise, a phosphate of copper. Variscite is a blue-green phosphate sometimes used as an imitation of turquoise. Callais is variscite from Spain and France that was used in the Early Neolithic as a pigment and to make trade beads. 

A blue colour is also given by phosphates, arsenates, silicates, or borates. 

This chargeless molecule can be extracted by ether or amyl alcohol. In addition to this a set of complex ions, such as [Fe(SCN)]2+, [Fe(SCN)2]+, [Fe(SCN)4]-, [Fe(SCN)5]2-, and [Fe(SCN)6]3 are also formed. The composition of the product in aqueous solution depends mainly on the relative amounts of iron and thiocyanate present. Phosphates, arsenates, borates, iodates, sulphates, acetates, oxalates, tartrates, citrates, and the corresponding free acid interfere due to the formation of stable complexes with iron(III) ions. 

Blue residue. 2. Green residue. 3. Pink residue. A1203, phosphates, arsenates, silicates, borates. ZnO. MgO. ... 

Phosphates, arsenates, and arsenites are generally insoluble those of Na, K, and NH4 are soluble. 

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