Hydrolysis precipitation

Chemical reactions can also affect the k and k terms and thereby influence or control coUoidal stabUity (21,121). Pertinent examples are dissolution, precipitation, hydrolysis, precipitation, and chemical complexing. The last reaction may involve either simple species, eg. 

Dousma, J. de Bruyn, P.L. (1976) Hydrolysis-precipitation studies of iron solutions. I. Model for hydrolysis and precipitation from Fe(III) nitrate solutions. J. Colloid Interface Sci. 56 527-539... 

Upon dilution, ferric sulphate solutions readily undergo hydrolysis, precipitates being obtained which, however, have no well-defined composition.7... 

Reactions such as dissolution, hydrolysis, precipitation, photolysis, adsorption/desorption, oxidation-reduction, ion exchange, complexation, biodegradation, polymerization, and others taking place in the environment, may affect the solubility of pollutants and therefore their mobility, specia-tion, and toxicity. This, in turn, can define to a great extent the dispersion, bioavailability, and risk associated with them. 

Then the chalcogenide ions will combine with the metal ions released from the thiosulfate/selenosulfate complexes, and upon hydrolysis precipitating the corresponding chalcogenides. Due to the differences in the stabihty of the metal-chalcogenide complexes initially formed, the optimal concentrations, pH, and temperatures may vary from one chalcogenide to another. Optimal experimental conditions must be estabhshed for each system. 

Chemical reactions that occur within the crevice are extremely important to the initiation and stabilization of crevice corrosion, as well as in the determination of its penetration rate. The three major types of chemical reactions that influence the chemical environment within an occluded region are hydrolysis, precipitation, and chemical dissolution. 

They therefore took advantage of the iron hydrolysis - precipitation and acid regeneration process that occurs con-currently with leaching at elevated temperatures in pressure acid leaching (PAL). It was noted that PAL residues contained significant quantities of sulfate, consistent with precipitation of hydronium alunite, H30.Al3(S04)2(0H)6. 

Fe(N03)3 solutions. Precipitates formed from 6.25 x I0 and 6.25 x lO M Fe(N03)3 solutions at 24 and 55 C showed the characteristic pattern of a-FeOOH, whereas in 6.25 x lO M, Fe(N03)3 solution at 24°C an amorphous precipitate was formed. a-Fe203 precipitated at 90 °C. The same authors proposed (Fig. 23.2) the mechanism of hydrolysis-precipitation from Fe(N03)3 solutions, consisting of the hydrolysis to monomers (A) and dimers (B), reversible, rapid growth of small polymers (C), the formation of slowly reacting large polymers (D), and polymerization and oxolation with the formation of a solid phase (E). XRD, FT-IR, and Mbssbauer spectroscopies were used to characterize hydrolytical solid products obtained by the hydrolysis of O.l M Fe(N03)3 aqueous solutions at 90°C in the presence of hexamethylenetetramine (HMTA) [24,25]. HMTA generates OH ions at an elevated temperature in accordance with the chemical reactions... 

Proposed scheme of hydrolysis/ precipitation from an aqueous Fe(N03)3 solution. 

Iodide, added in small portions to Au (with H30 from hydrolysis) precipitates yellow AuI when equivalent quantities are combined. The precipitate is insoluble in H2O but soluble in excess reagent ... 

This reaction provides a test applicable to sihcic acid, silica or a silicate. One treats a sample with HF (or CaF2 as above, warmed). Some of the released SiF4 is absorbed in a drop of H2O suspended over the reaction mixture. Hydrolysis precipitates silicic acid, visible in the drop, e.g. ... 

The hydrolysis of PVA-QA was measured in the presence of four metals, Co(II), Zn(II), Cu(II), and Ni(II). The first order rate constants (kobs) observed in the presence of a 5 1 or greater excess of each metal are listed in Table I. The rate of hydrolysis at pH 7.5 in the absence of metals was not measurable. The kinetics of hydrolysis in the presence of a 4 1 ratio of Cu(II) was biphasic, consisting of two simultaneous first order processes. The contribution of the faster component diminished as the Cu(II) PVA-QA ratio was decreased to 1 1. A single first order process was observed in the presence of Ni(II), Co(II), and Zn(II). A double reciprocal plot of k obs vs. [M]- for Ni(II) exhibited the expected linearity. Utilizing Equation 6, the value of k3 derived from the intercept of this plot was 0.013 min". Similar but less reproducible results were obtained for Co(II)-promoted hydrolysis. Precipitation of Zn(0H)2 prevented the use of this metal above a concentration of 1.7 X 10 M, and a maximum zinc(II) chelator ratio of 7 1. 

Reaction results in a mixture of the three types of c. The largest amount, P-c., is separated from the others by crystallization after inactivating the enzyme, removing unreacted starch by hydrolysis, precipitation of the c. by acetone, and purification. 

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