Phosphoric acid concentration step

The principal disadvantage of the acid process is the higher capital cost involved mainly because of more processing steps and the corrosivity of hot, concentrated phosphoric acid which requires a reactor built from dense graphite. 

Solvent extraction—purification of wet-process phosphoric acid is based on preferential extraction of H PO by an organic solvent vs the cationic impurities present in the acid. Because selectivity of acid over anionic impurities is usually not sufficient, precipitation or evaporation steps are included in the purification process for removal. Cmde wet-process acid is typically concentrated and clarified prior to extraction to remove post-precipitated sludge and improve partition of the acid into the solvent. Concentration also partially eliminates fluoride by evaporation of HF and/or SiF. Chemical precipitation of sulfate (as Ba or Ca salts), fluorosiUcates (as Na salt), and arsenic (as sulfides) may also be used as a prepurification step preceding solvent extraction. 

Hydrolysis of diphenyl phosphorochloridate (DPPC) in 2.0 M aqueous sodium carbonate is also believed to be a two-phase process. DPPC is quite insoluble in water and forms an insoluble second phase at the concentration employed (i.e. 0.10 M). It seems highly significant that the hydrophobic silicon-substituted pyridine 1-oxides (4,6,7) are much more effective catalysts than hydrophilic 8 and 9. In fact, 4 is clearly the most effective catalyst we have examined for this reaction (ti/2 < 10 min). Since derivatives of phosphoric acids are known to undergo substitution reactions via nucleophilic addition-elimination sequences 1201 (Equation 5), we believe that the initial step in hydrolysis of DPPC occurs in the organic phase. Moreover, the... 

As long as the soda pop is carbonated, the carbonic acid is present along with the phosphoric acid, although at a much smaller concentration. Citric acid may also be present, but at a smaller concentration. The carbonic acid may be eliminated by degassing to remove the carbon dioxide. Your instructor may ask you to obtain titration curves (step 4 below) for both as received samples and... 

Figure 2.1.1 shows the most common derivatisation methods for anionic surfactants reported in the literature [1]. The first method of LAS determination by GC consisted of a microdesulfonation procedure in which LASs were desulfonated in boiling phosphoric acid at high temperature [2-4] and the corresponding alkylbenzenes analysed. The microdesulfonation method was further improved by introducing additional concentration and clean-up steps [5—11], which allowed the determination of LAS in influent, effluent and river water samples at low qg L-1 levels [7,8] and sediment and sludge samples [8] at pg g-1. In addition to the desulfonation procedure, several derivatisation techniques have been used to make LAS analysis amenable to GC. 

The phosphate concentration in the tailings is upgraded to a level adequate for commercial exploitation through removal of the nonphosphate sand particles by flotation [32], in which the silica solids are selectively coated with an amine and floated off following a slurry dewatering and sulfuric acid treatment step. The commercial quality, kiln-dried phosphate rock product is sold directly as fertilizer, processed to normal superphosphate or triple superphosphate, or burned in electric furnaces to produce elemental phosphorus or phosphoric acid, as described in Section 9.2. 

Consulting the table of the dissociation constants K s for phosphoric acid shows that the first dissociation is much greater than the second, about 100,000 times greater. This means nearly all the W(aq) in the solution comes from the first step of dissociation. The second and third steps add very little Y (aq) to the solution. So a solution of phosphoric acid will contain H3PO4 molecules in highest concentration with smaller, and nearly equal, concentrations of H and H2PO4. The HPO4 and PO4 ions are present in very small concentrations. 

As described in Figure 3.7, TRU separation is performed by implementing the DIDPA process on pretreated PUREX raffinates. A front-end denitration step by formic acid is thus required to reduce the nitric acid concentration of the feed down to 0.5 M to allow the TRU elements to be extracted by the cation exchanger di-fvo-dccyl-phosphoric acid (DIDPA). This preliminary step, however, induces the precipitation of Mo and Zr (and thus the potential carrying of Pu), which requires filtration steps. The TRU and Ln(III) elements are coextracted by a solvent composed of the dimerized DIDPA and TBP, dissolved at 0.5 and 0.1 M, respectively, in n-dodecane. The An(III) + Ln(III) fraction is back-extracted into a concentrated 4 M nitric acid solution, whereas Np and Pu are selectively stripped by oxalic acid. 

In the PhoSAI process of Scottish Agricultural Industries (Figure 12.1), ammonia reacts with phosphoric acid (minimum concentration 42 % P2O5) in a stirred-tank reactor to produce a slurry with an N/P ratio of 1.4 (the point of maximum solubility) under atmospheric pressure. The slurry flows to a pin mixer in which the N/P ratio is brought back to 1.0 by the addition of more concentrated phosphoric acid. During this step the solubility decreases and more water vaporizes due to the heats of reaction and crystallization. A solid product is formed that typically contains 6% to 8 % moisture. The product is screened, the oversize particles are ground and the product is sent to storage296. 

For almost all types of steel there is a similar problem in the dissolution step. Three elements, Al, Si, and W, behave differently in the analysis of the total content and require special methods. These methods are simple extensions of the technique, which in the case of the determination of acid soluble Al or Si, can simply be omitted. When, during the dissolution, an oxide residue remains, which in general consists of Si02 or A1203, this must be brought into solution with a fusion, and added to the rest of the sample. If the W concentration is higher than 0.5%, the dissolving acid solution should also include phosphoric acid. Thus, it is possible to produce a universal method for the elements that are contained in steel and which influence its properties. 

A mixture of the Step 1 product (1.0 g), 20 ml of deionized water, and 5% phosphoric acid was stirred for 3 hours at ambient temperature and then treated with sodium chloride (l.Og) and sufficient O.IM sodium hydroxide to obtain a pH of 6.8. The product was extracted three times with 20 ml of CH2CI2, dried with MgS04, concentrated, and 82 g of product were isolated. 

The Step 4 product was dissolved in an aqueous solution containing phosphoric acid at pH 1 and stirred for 2 hours at between 40° C and 5 0° C. After cooling the reaction mixture to ambient temperature, the pH was raised to 6 using 5% aqueous NaHCOa solution. Brine was then added, and the resulting mixture extracted twice with CH2CI2. The extract was dried over MgS04, filtered, and concentrated. Precipitation was induced by the addition of diethyl ether to the residue, and the product was isolated as a white powder. 

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