Solubility various phosphates

Pyrite is not only one of the key compounds in Wachtershauser s theory, but could also have fulfilled an important function for phosphate chemistry in prebiotic syntheses. A group in Rio de Janeiro studied the conditions for phosphate sorption and desorption under conditions which may have been present in the primeval ocean. In particular, the question arises as to the enrichment of free, soluble inorganic phosphate (Pi), which was probably present in low concentrations similar to those of today (10 7-10 8M) (Miller and Keffe, 1995). Experiments show that acid conditions favour sorption at FeS2, while a weakly alkaline milieu works in an opposite manner. Sorption of Pi can be favoured by various factors, such as hydrophobic coating of pyrite with molecules such as acetate, which could have been formed in the vicinity of hydrothermal systems, or the neutralisation of mineral surface charges by Na+ and K+. 

Phosphatic fertilizers usually contain a mixture of phosphates exhibiting varying degrees of solubility, which also depend on the nature of the soil. It is therefore necessary to analyse for these various phosphate types. A list of various phosphate compounds, their molecular formulae and solubilities, where known, is given in Table 6.1. 

The stabilizing effect of buffers that have multiple charged species in solution should also be investigated to determine the potential reaction between excipients and API. For example, buffers that use carbonates, citrate, tartrate, and various phosphate salts may precipitate with calcium ions by forming sparingly soluble salts. However, this precipitation is dependent upon the solution pH. Because phosphate can exist in mono-, di-, and tribasic forms, each calcium salt has its own solubility product, and precipitation will only occur when one of the solubility product is exceeded. Calcium ions may also interact or chelate with various amino acids, and other excipients, which may also lower the effective concentration of calcium that is capable of interacting with phosphate ions. Finally, the activity of phosphate ions may be lowered due to interactions with other solution components. 

Freezing milk causes crystallization of pure water and the unfrozen liquid becomes more saturated with respect to various salts. Some soluble calcium phosphate precipitates as Ca,(POj2, with the release of H+ and a decrease in pH (e.g. to 5.8 at — 20°C). 

To evaluate the leaching performance of the waste streams, we assume that soluble and sparsely soluble compounds will leach out and fail the TCLP and, hence, should be target contaminants for stabilization. These soluble or sparsely soluble components may directly be treated with phosphates and converted to their insoluble, nonleachable forms. The literature is full of studies on stabilization of such divalent hazardous metal contaminants (Pb, Cd, and Zn, in particular), where treatment with various phosphates has been elfective. These studies are summarized in Section 16.3. 

Example 8.17. Phosphate Binding in Soils The availability of phosphate for plants depends in various ways on the pe above all, the interactions of phosphates with Fe(II) and Fe(III) are of importance. The surfaces of Fe(III)(hydr)oxides can adsorb phosphate this adsorption is pH dependent. Here we consider the pe-dependent solubility of phosphate as strengite, FeP04 2 H20(s), and vivianite, Fe3(P04)2 8 H20(s). The following equilibria are given ... 

In sequestration (chelation) the hardness ions are bound to the builder in the form of soluble complexes. Phosphates, citrates, and nitrilotriacetic acid (NTA) are examples of this class of builder compound. Table 8.3 lists the calcium binding capacities of various builders. Other strongly chelating compounds exist, such as phosphonates and EDTA, but they are generally not extensively used in HDLDs. The most efficient builder is sodium tripolyphosphate (STPP). Unfortunately, tripolyphosphate has been identified as a possible cause of eutrophication in lakes and rivers. It is severely controlled and even banned in several countries. As a result, most countries in North America and Europe have converted to nonphosphate formulations. Other regions are also gradually imposing restrictions on the use of phosphates. 

Readily available phosphorus This form is present in soil pore water and the exchangeable pool. Phosphorus in this pool is continuously replenished from other stable pools at various rates, depending on the solubility of phosphate minerals and the physicochemical properties of soils. Inorganic phosphorus is extracted with neutral salts such as NaCl, KCl, NH4CI, and NaHCOj. 

Various phosphates are produced from phosphoric acid which is made either by adding sulphuric acid to phosphate rock (wet process) or by burning phosphorus in air to give phosphorus pentoxide, which is then hydrated. Major uses of phosphoric acid are the production of phosphate and compound fertilizers, formation of sodium tripolyphosphate (which is used as a builder in detergents where it forms stable water-soluble complexes with calcium and magnesium ions) and the production of organic derivatives like triphenyl and tricresyl phosphate. These are used as plasticizers for synthetic polymers and plastics. 

Relatively small amounts of pure DAP and MAP are made by crystallization processes using phosphoric acid made by the electric-furnace process or using wet-process acid purified by any of various processes. The pure, fully soluble ammonium phosphates are used mainly for specialty liquid fertilizers. 

The ability of the polyphosphates to form water-soluble complexes with calcium has been known for a long time. The phenomenon of binding alkaline earth ions in soluble complexes, and thus preventing the formation of undesirable precipitates, is generally called sequestration. This was the subject of earlier patent literature. The role of these calcium-polyphosphate complexes in softening of water was described in Chapter 23 of the book edited by Bailar. The complexing of a number of metal ions with the various phosphates was reviewed in detail in 1958. ... 

Fig. 6.20A-F. Changes in various phosphate components in the roots (a), shoots (x) and non-axial parts —NAP ( ) of germinated oat seedlings. (A) Fresh weight, (B) Total phosphate, (C) Acid soluble phosphate. In the NAP this is comprised mainly of phytic acid, and in the shoot and root of inorganic phosphate and some acid soluble organic phosphate (but no phytic acid), (D) Nucleic acid phosphate, (E) Lipid phosphate, (F) Protein phosphate. Based on Hall and Hodges, 1966 [58]...

Before enterii the livii world, the phosphoric add in inorganic compounds must first be mobilized. This is brought about by the liberation of various strong adds into the soil by numerous aerobic and anaerobic micro-organisms. The COj liberated by the roots of plants and by bacteria also plays a part. Once rendered soluble the phosphates may be repredpitated or assimilated by plants and then passed to animals in organic or inorganic combination. The excreta of animals and the dead bodies of plants and animals return to the soil the phosphates which have been removed. In this way a local accumulation of phosphate may be obtained and used as fertilizer. 

Sulfide collectors ia geaeral show Htfle affinity for nonsulfide minerals, thus separation of one sulfide from another becomes the main issue. The nonsulfide collectors are in general less selective and this is accentuated by the large similarities in surface properties between the various nonsulfide minerals (42). Some examples of sulfide flotation are copper sulfides flotation from siUceous gangue sequential flotation of sulfides of copper, lead, and zinc from complex and massive sulfide ores and flotation recovery of extremely small (a few ppm) amounts of precious metals. Examples of nonsulfide flotation include separation of sylvite, KCl, from haUte, NaCl, which are two soluble minerals having similar properties selective flocculation—flotation separation of iron oxides from siUca separation of feldspar from siUca, siUcates, and oxides phosphate rock separation from siUca and carbonates and coal flotation. 

Because monocalcium phosphate is incongmently soluble, it is typically contaminated with various amounts (6—10%) of dicalcium phosphate and free phosphoric acid resulting from in-process disproportionation of the monocalcium salt. Free phosphoric acid may render the product hygroscopic, and absorbed water plus acid catalyzes further decomposition to additional free acid and dicalcium phosphate. For this reason, industrial monocalcium phosphate may contain some dicalcium phosphate resulting from excess lime addition and then aged to ensure the removal of residual free phosphoric acid. 

The characteristics of soluble sihcates relevant to various uses include the pH behavior of solutions, the rate of water loss from films, and dried film strength. The pH values of sihcate solutions are a function of composition and concentration. These solutions are alkaline, being composed of a salt of a strong base and a weak acid. The solutions exhibit up to twice the buffering action of other alkaline chemicals, eg, phosphate. An approximately linear empirical relationship exists between the modulus of sodium sihcate and the maximum solution pH for ratios of 2.0 to 4.0. 

Molybdenum blue method. When arsenic, as arsenate, is treated with ammonium molybdate solution and the resulting heteropolymolybdoarsenate (arseno-molybdate) is reduced with hydrazinium sulphate or with tin(II) chloride, a blue soluble complex molybdenum blue is formed. The constitution is uncertain, but it is evident that the molybdenum is present in a lower oxidation state. The stable blue colour has a maximum absorption at about 840 nm and shows no appreciable change in 24 hours. Various techniques for carrying out the determination are available, but only one can be given here. Phosphate reacts in the same manner as arsenate (and with about the same sensitivity) and must be absent. 

The chosen coordinates defining minimum/maximum pH levels and minimum/maximum phosphate (as ppm P04) led to the production of various coordinated phosphate program control charts for different pressure ratings (maximum phosphate solubility is a function of pressure). The area within the coordinates providies a simple control box for BW testing purposes. 

The most critical decision to be made is the choice of the best solvent to facilitate extraction of the drug residue while minimizing interference. A review of available solubility, logP, and pK /pKb data for the marker residue can become an important first step in the selection of the best extraction solvents to try. A selected list of solvents from the literature methods include individual solvents (n-hexane, " dichloromethane, ethyl acetate, acetone, acetonitrile, methanol, and water ) mixtures of solvents (dichloromethane-methanol-acetic acid, isooctane-ethyl acetate, methanol-water, and acetonitrile-water ), and aqueous buffer solutions (phosphate and sodium sulfate ). Hexane is a very nonpolar solvent and could be chosen as an extraction solvent if the analyte is also very nonpolar. For example, Serrano et al used n-hexane to extract the very nonpolar polychlorinated biphenyls (PCBs) from fat, liver, and kidney of whale. One advantage of using n-hexane as an extraction solvent for fat tissue is that the fat itself will be completely dissolved, but this will necessitate an additional cleanup step to remove the substantial fat matrix. The choice of chlorinated hydrocarbons such as methylene chloride, chloroform, and carbon tetrachloride should be avoided owing to safety and environmental concerns with these solvents. Diethyl ether and ethyl acetate are other relatively nonpolar solvents that are appropriate for extraction of nonpolar analytes. Diethyl ether or ethyl acetate may also be combined with hexane (or other hydrocarbon solvent) to create an extraction solvent that has a polarity intermediate between the two solvents. For example, Gerhardt et a/. used a combination of isooctane and ethyl acetate for the extraction of several ionophores from various animal tissues. 

Alkoxylated polysiloxanes are a relatively new class of dyebath lubricants. They have practically no substantivity for the substrate, yet combine adequate lubrication with water solubility and easy rinsability. If the silicones contain primary hydroxy groups, these can be modified by esterification, phosphation, phosphonation, sulphation, sulphonation or carboxylation. These anionic substituents confer substantivity for various substrates without losing rinsability. Anionic organic sulphates and sulphonates probably offer the best overall properties for dyebath lubricants, whilst other types can be more suitable for selected applications [464]. 

Most primary and secondary minerals found in soil systems are barely soluble in the soil solution. The amount of mass from the bulk phase to hydrated ions in soil solution is negligible compared to the total mass of the solid phase. In arid and semi-arid soils, concentrations of most trace metals in soil solution may be controlled by their carbonates and to some extent by their hydroxides. Other than carbonates, trace elements in arid and semi-arid soils may also occur as sulfate, phosphate or siliceous compounds, or as a minor component adsorbed on the surface of various solid phase components. The solubility of carbonates, sulfates and other common minerals of trace elements in arid and semi-arid soils will be discussed in Chapter 5. Badawy et al. (2002) reported that in near neutral and alkaline soils representative of alluvial, desertic and calcareous soils of Egypt, the measured Pb2+ activities were undersaturated with regard to the solubility of... 

---