Precipitation of solids

Although lubricant base stocks have been subjected to dewaxing processes, they still contain large amounts of paraffins that result in a high pour point for the oil. In the paragraph on the cold behavior of diesel fuels, additives were mentioned that modify the paraffin crystalline system and oppose the precipitation of solids. 

Occasionally precipitation of solid salt (FeCl2.iH20)... 

In particular, if we raise the temperature, there will occur some change which will give rise to absorption of heat. If a saturated solution of potassium nitrate is in equilibrium with crystals of solid salt at a particular temperature, and if we now raise the temperature, a change must occur which absorbs heat and so tends to cool the system. This is the dissolution of more solid, because the heat of solution is positive, that is, heat is absorbed when salt goes into solution. But if we have a saturated solution of calcium sulphate, there will occur a precipitation of solid on warming, because the heat of solution is negative, and heat is absorbed when salt comes out of solution. 

Three processes that take place in living organisms - respiration in animals and plants, photosynthesis only in plants, and the precipitation of solids by some aquatic animals - have altered the primeval composition of the outer solid, liquid, and gaseous layers of the earth. Respiration consumes oxygen from the atmosphere and creates carbon dioxide. Photosynthesis, which does the opposite (consumes carbon dioxide and releases oxygen), has... 

The aluminium is white and shiny before applying the potential. A critical potential exists below which no electro-oxidation will commence. At more extreme potentials, the surface atoms of the aluminium oxidize to form Al3+ ions, which combine with oxide ions from the water to form AI2O3. This electro-precipitation of solid aluminium oxide is so rapid that molecules of dye get trapped within it, and hence its coloured aspect. 

It is important that sufficient time be allowed for proper partitioning between the phases. The heating tape maintains the temperature in the desired range, preventing the precipitation of solids and allowing for better separation. The phases should be allowed to separate for at least 15 min. If a small amount of solids is observed, this should not interfere with the separation and the solids may be discarded with the aqueous phase. 

It is necessary to consider a number of equilibrium reactions in an analysis of a hydrometallurgical process. These include complexing reactions that occur in solution as well as solubility reactions that define equilibria for the dissolution and precipitation of solid phases. As an example, in analyzing the precipitation of iron compounds from sulfuric acid leach solutions, McAndrew, et al. (11) consider up to 32 hydroxyl and sulfate complexing reactions and 13 precipitation reactions. Within a restricted pH range only a few of these equilibria are relevant and need to be considered. Nevertheless, equilibrium constants for the relevant reactions must be known. Furthermore, since most processes operate at elevated temperatures, it is essential that these parameters be known over a range of temperatures. The availability of this information is discussed below. 

We will now look at the relative amounts of ions in solution at the very end of the titration, i.e. after the end point has been reached and surpassed, and note that all of the chloride ion will have been consumed by the precipitation of solid AgCl, and that the addition offurther AgNO3 solution to the reaction solution merely dilutes it. At the end of the titration, we see that [C/ ] [Ag+]. 

Triturating the mixture with hexanes and storing overnight at 0°C induces the precipitation of solid (R)-Tol-BINAP, which is then removed by filtration. 

Centrifuging is employed for washing and separating jelly-like precipitates (hydroxides, sulphides). The precipitation of solid phase particles is accelerated under the effect of the centrifugal force developed in the rapid rotation of a centrifuge. 

The dashed lines in (7.90) illustrate an expected cooling path for a liquid chosen to be of initial concentration v = xB — 0.1. As cooling proceeds (1), the first precipitate of solid a appears when the cooling path meets the a-liquidus curve. Thereafter, as solid a proceeds to freeze out of solution, the melt is successively depleted of component A and moves down the a-liquidus curve (2) toward the eutectic point. At this point, the remaining liquid freezes to a mix of solid a and /3 (in proportion to eutectic composition), and the mix of solids... 

Precipitation of solids with dense gases Z. Knez", E. Weidner6... 

Sulfide. Sulfide appears in the water column of Lake Greifen only at the end of stagnation time and in the deepest water layers. This distribution indicated the biological reduction of sulfate in sediments. The reactions involved in the sulfur cycle are described in ref. 65. The occurrence of sulfide indicates a very low pe (p < 0) sulfide is an efficient reductant for many elements, including Fe(III), Mn(IV), As(V), and Cr(VI). The occurrence of sulfide also implies the possible precipitation of solid sulfide phases of various elements and the formation of dissolved complexes (21-23). 

When drops of hydrochloric acid fall into an aqueous solution of silver nitrate, a precipitate of solid silver chloride forms immediately. However, close inspection of the solid and the solution would show that there is a continuing interchange between the silver and chloride ions in the solid and the solution. 

The sea water was obtained from La Jolla and was concentrated to half its original weight before dilution. Just enough sulfuric acid was added to prevent the precipitation of solids during the concentration. This procedure may alter the salt composition somewhat, but it is representative of most evaporation processes. 

Addition of a solution of sodium chloride to a solution of silver nitrate yields a white precipitate of solid silver chloride. 

A compound of formula XC13 reacts with aqueous AgN03 to yield a precipitate of solid AgCl according to the following equation ... 

Another way to measure Ksp for CaF2 is to approach the equilibrium from the opposite direction—that is, by mixing sources of Ca2+ and F ions to give a precipitate of solid CaF2 and a saturated solution of CaF2. Suppose, for example, that we mix solutions of CaCl2 and NaF, allow time for equilibrium to be reached, and then measure [Ca2+] = 1.5 X lCT4Mand [F ] = 1.0 X 10 3 M. These ion concentrations yield the same value of Ksp ... 

The following pictures represent solutions of Ag2CrC>4, which also may contain ions other than Ag+ and Cr042- that are not shown. Solution (1) is in equilibrium with solid Ag2Cr04. Will a precipitate of solid Ag2Cr04 form in solutions (2)—(4) Explain. 

Aerosol Solvent Extraction System (ASES) Here, the solution is sprayed through atomization nozzle into a chamber L lied with SCF. Expansion of solution occurs within the Lne droplets of solvent being sprayed, thus creating supersaturation and precipitation of solids as Lne particles. 

Z. Knez, E. Weidner, Precipitation of solid with dense gases, in A. Bertucco, G. Vetter (Eds.), High Pressure Process Technology Fundamentals and Applications, Elsevier, 2001, pp. 587-611. 

Table 3.2 summarizes the chemistries that lead to the precipitation of solid phases. The actual parameters for these equilibria are in Appendix B. The range of temperatures used in model parameterizations or validation and the maximum molal concentrations are both fundamentally important in properly applying the model. Extrapolations outside these tempera-ture/compositional ranges require careful scrutiny of model calculations. 

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