Phosphate stabilization principles

Phosphate stabilization of municipal solid waste combustion residues geochemical principles... 

Fig. 1. Schematic of chemical stabilization principle. Soluble phases are converted to insoluble phosphate minerals.

The principles of the above reactions form the basis of a series of important metabolic interconversions involving the coenzyme pyridoxal phosphate (structure 2.41). This condenses with amino acids to form a Schiff base (structure 2.42). The pyridine ring in the Schiff base acts as an electron sink which very effectively stabilizes a negative charge. 

The various reactions of pyridoxal phosphate in amino acid metabolism shown in Table 9.1 all depend on the same chemical principle - the ability to stabilize amino acid carbanions and to labilize bonds about the a-carbon, by... 

Continuous-monitoring methods for assay of TR-ACP activity are based on the principle introduced by Hillmann in which a-naphthoi released from its phosphate ester forms a colored product with the stabilized diazonium salt of 2-amino-5-chlorotoluene-1,5-naphthalene disulfonate (Fast Red TR). The introduction of alcohols, such as 1,5-pen-tanediol, accelerates the reaction and increases sensitivity by acting as phosphate acceptors in transfer reactions. The addition of sodium tartrate inhibits the sensitive isoenzymes (i.e., prostatic and lysosomal ACPs) if they are present in the sample. 

Substantial numbers of important agrochemicals contain the carbonyl groups noted earlier, so that abiotic hydrolysis may be the primary reaction in their transformation the example of carbaryl has already been cited (Wolfe et al. 1978a). The same general principles may be extended to phosphate and thiophosphate esters, although in these cases, it is important to bear in mind the stability to hydrolysis of primary and secondary phosphate esters under neutral or alkaline conditions that prevail in most natural ecosystems. On the... 

Figure 1 Schematic drawing of the various ways in which metal ions can, in principle, facilitate hydrolysis of a phosphate ester by providing a coordinated nucleophile, activating the substrate and stabilizing the transition state, and stabilizing the laving group. Similar factors are operative for hydrolysis of amide bonds.

The most successful method developed for the production of a general-purpose synthetic rubber was the emulsion copolymerization of butadiene and styrene (SBR), which still represents the main process in use today [54,64-69]. The general principles of copolymerization will be discussed in a later section, but it is instructive at this point to examine the other main features of this system. The types of recipes used are seen in Table V [67]. The recipes shown are to be considered only as typical, as they are subject to many variations. It should be noted that the initiator in the SO C recipe (hot rubber) is the persulfate, whereas in the recipe (cold rubber) the initiator consists of a redox system comprising the hydroperoxide-iron(II)-sulfoxylate-EDTA. In the latter case, the initiating radicals are formed by the reaction of the hydroperoxide with the ferrous iron, whose concentration is controlled by the EDTA complexing agent the sulfoxylate is needed to convert the oxidized ferric(III) back to ferrous iron. The phosphate salt serves as a stabilizing electrolyte for the latex. 

These techniques are bas not only on the principle that lead-containing phosphates with the apatite structure are highly insoluble, but also that rapid reactions occur with apatite and lead ions at the sohd/aqueous solution interface [12, 13, 15, 20, 29, 48, 53, 56]. Removal of lead from aqueous solutions using synthetic hydroxyapatite gives aqueous lead concentrations below the maximum contamination level after Ih [12, 53]. Other workers [9] observed the formation of calcium-lead apatite solid-solutions after 3 mins contact between synthetic hydroxyapatite and aqueous solutions containing lead, and no lead was detected in the aqueous solution after 24 h contact. However, the efficiency of lead removal depends on the characteristics of the phosphate rock employed [15]. It has been shown that the composition and crystallinity of the phosphate influence the speed of the surface reactions [4, 44]. More highly crystalline solids have lower solubilities and dissolution rates, making the apatite less reactive [4]. The presence of fluoride in the hydroxyapatite structure decreases its solubility and dissolution rate, while the presence of carbonate decreases structural stability, and increases solubility and the dissolution rate [4, 35]. 

---