Mixing precipitation

Grams of mixed precipitate 1 = grams CaCOa -I- grams MgCOa... 

The amount of iron and manganese in an alloy can be determined by precipitating the metals with 8-hydroxyquinoline, C9H7NO. After weighing the mixed precipitate, the precipitate is dissolved and the amount of 8-hydroxyquinoline determined by another method. In a typical analysis, a 127.3-mg sample of an alloy containing iron, manganese, and other metals was dissolved in acid and... 

Baldyga, J., Podgorska, W. and Pohorecki, R., 1995. Mixing-precipitation model with application to double feed semibatch precipitation. Chemical Engineering Science, 50, 1281-1300. 

The calculations were made based on the uniformly mixed precipitation kinetics model (Fig. 1.52) for one component and one dimensional system represented by Eq. (1-20). 

Precipitation may be significant for heavy metals and other inorganic constituents in injected wastes. For example, sulfide ions have a strong affinity for metal ions, precipitating as metal sulfides. The dissolved constituents in injected wastes and reservoir fluids would not be in equilibrium with the in situ brines because of the fluids different temperature, pH, and Eh. When the fluids are mixed, precipitation reactions can lead to injection-well plugging. 

Verbeeck (66) found that the solubility behavior could be explained by assuming ideality his value for the logarithm of the solubility product of pure strontiumhydroxyapatite was -52.3. Hence, the value of D is 18 in favour of Ca incorporation and against Sr incorporation in mixed precipitates. This seems to be in agreement with discrimination against strontium in the bones and teeth of living organisms. 

Even though many ionic compounds dissolve in water, many others do not. If the attraction of the oppositely charged ions in the solid for each other is greater than the attraction of the polar water molecules for the ions, then the salt will not dissolve to an appreciable amount. If solutions containing ions such as these are mixed, precipitation will occur, because the strong attraction of the ions for each other overcomes the weaker attraction for the water molecules. 

Thus rate laws for precipitation reactions tend to be complicated, even in pure solutions. Mixed precipitates can be inhomogeneous solids with one component restricted to a thin outer layer because of slow diffusion. New solid phases can precipitate homogeneously onto the surfaces of existing solid phases. Weathering solids may provide host surfaces onto which more stable phases may precipitate. 

Nickel removed by coprecipitation can be remobilized by microbial action under anaerobic conditions (Francis and Dodge 1990). Remobilization results Ifom enzymatic reductive dissolution of iron with subsequent release of coprecipitated metals. A lowering of pH as a result of enzymatic reactions may indirectly enhance the dissolution of nickel. Experiments using mixed precipitates with goethite... 

Complex oxides of ceria were formed by pyrolysis of mixed precipitation from aqueous solution. Table I shows the XRD results of Ce La and Ce Zr mixed oxides calcined at 1,000°C (Matsumoto et al., 1991). These results... 

Zinc and Cadmium Sulfides and Sulfoselenides. The raw materials for the production of these sulfide phosphors are high-purity zinc and cadmium sulfides, which are precipitated from purified salt solutions by hydrogen sulfide or ammonium sulfide [5.291], [5.296], [5.307], [5.310], The concentration of contaminants such as Fe, Co, or Ni must be below 1 % of the activator concentration. The Zn, Cd S can be produced by mixing precipitated zinc sulfide and cadmium sulfide. However, coprecipitation from mixed zinc-cadmium salt solutions is preferred because of the better homogeneity. 

Zirconium can be removed from the mixed precipitated acids by fusing them with potassium carbonate and extracting the melt with cold water. The niobium and tantalum pass into solution as niobate and tantalate of potassium respectively, while the zirconium remains undissolved as the dioxide, Zr02.4 The method is more suited for the removal of zirconium from niobates than from tantalates.3... 

Lead acetate Potassium dichromate and concentrated sulfuric acid Sodium nitrite Copper sulfate Mercury (II) chloride Yellow precipitate of lead iodide soluble in excess hot water Liberation of iodine Liberation of iodine Brown mixed precipitate Scarlet precipitate of mercury (II) iodide... 

Scrap zinc or concentrated zinc ores are dissolved in sulfuric acid, the solution is purified, and the two solutions are reacted. A heavy mixed precipitate results that is 28 to 30% zinc sulfide and 72 to 70% barium sulfate. 

An alloy containing only cadmium and zinc is claimed by the manufacturer to contain 63-percent cadmium by weight. A 356-mg sample of the alloy is dissolved in nitric acid, the solution buffered, and both ZnS and CdS are precipitated by treatment with H2S. The mixed precipitate is dissolved in a solution containing 5 millimoles of ferric sulfate, precipitating sulfur. The filtrate is acidified and the divalent iron is titrated with standard KMn04, 1.60 millimoles of the latter being consumed. How nearly correct is the manufacturer s estimate ... 

It should be noted that, for higher values of Cr %, equilibria for polymeric species should be included and that Cr(OH)3 may precipitate. In the presence of iron, the mixed precipitate FexCri x(OH)3 may be formed. 

Besida and O Donnell [53] showed that addition of NaF-HF to the yellow-orange solutions of Ti2+ in SbF5-HF produced mixed precipitates of blue TiF3, white TiF4 and black metallic Ti and the supernatant solution was colorless. A complex pattern of disproportionation of Ti(II) to the element and to both Ti(III) and Ti(IV) simultaneously had occurred because of the insolubility of TiF3 in near-neutral HF. 

The mixed precipitate appears gray. This is an oxidation-reduction reaction, in which one mercury(I) ion in Hg2Cl2 is oxidized to Hg2+ in HgNH2Cl and the other mercury(I) ion is reduced to Hg, or elemental mercury. 

Experiment 193. — Mix 5 cc. each of lead nitrate and silver nitrate solutions, and add dilute hydrochloric acid drop by drop, until precipitation ceases. Allow the mixed precipitates of lead chloride and silver chloride to settle, decant the supernatant liquid down a glass rod, add a little water to the precipitate, and boil. Filter. Test portions of the filtrate for lead (see Exp. 177 (d ) and (e)). Test the precipitate for silver by (a) fusing a portion in the blowpipe flame, or (d) determining the solubility in ammonium hydroxide, or (c) exposing it to the sunlight (a change to purple indicates silver chloride). 

Experiment 194. — Mix 5 cc. each of lead nitrate, silver nitrate, and mercurous nitrate solutions, and add dilute hydrochloric acid drop by drop, until precipitation ceases. Separate and test the lead as in Exp. 193. Pierce a hole in the point of the filter paper with a glass rod, and wash the mixed precipitates of silver and mercurous chlorides into a test tube with dilute ammonium hydroxide. Warm gently and shake. Filter, and test the filtrate for silver as in Exp. 193. The black residue (see Exp. 166 (<2)).is a sufficient test for mercury. Its presence may be confirmed thus Dissolve the black precipitate in a very little aqua regia, dilute with water, and add a clean copper wire remove the wire in a few minutes, wipe gently, and mercury will be seen on the wire as a bright silvery coating. 

If the temperature falls below d, the solution solidifies it gives a mixed precipitate, formed of particles of the substance a and of h, whose average composition is well determined this composition is that of the solution of concentration 2. ... 

Mixed precipitation methods, i.e., PEG-assisted second antibody precipitation, are sometimes used for fraction separation, combining the specificity and low level of unspecific binding of the second-antibody method with the speed of PEG-based precipitation [127]. 

The mixed precipitate of double salt and ferrous ferricyanide is filtered out, washed to remove sulphates and sulphocyanides and decomposed by boiling with sodium carbonate, forming the sodium ferrocyanide and setting free the ammonia which is distilled off and collected. The sodium ferrocyanide solution is filtered off from the iron-lime precipitate, concentrated and crystallized as already described on page 404. Unfortunately the double salt precipitate is very difficult to wash, with the result that frequently considerable amounts of sulphates pass into the finished liquor as sodium sulphate. The first crop of crystals is normally a pure, high-grade sodium ferrocyanide. The first mother liquor is concentrated to proper density and crystallized in like manner. 

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