Chromium hydroxides

Chromium Hydroxide Green. This color additive is principally hydrated chromic sesquioxide [12182-82-0], -xHpD (Cl Pigment... 

Chromium hydroxide green is a more bluish and brilliant green than chromium oxide greens. It is quite transparent, and has good strength and excellent stabiUty. It is used in eye makeup and soap. 

Chromoxyd, n. chromium oxide, specif, chromic oxide, chromium(III) oxide. -farbe, /. chrome oxide color, -hydrat, n. chromium hydroxide, specif, chromic hydroxide, chro-mium(III) hydroxide, -natron, n. sodium chromite. -salz, n. chromic salt, chro-mium(III) oxide-... 

Another reason chemists find the above complex ion picture of aqueous solutions useful is that it is easily extended to explain amphoteric behavior. Take the case of chromium hydroxide, Cr(OH)3, a good example of an amphoteric hydroxide. It dissolves very little in water, but is quite soluble both in acid and in base. Presumably it can react with either. How can this behavior be explained in terms of the complex ion picture ... 

The following equations summarize the steps believed to occur when NaOH is slowly added to a solution of chromic ion. Step (4c) corresponds to formation of solid hydrated chromium hydroxide step (4d) corresponds to its dissolving in excess NaOH. 

When acid is added to a solution such as in equation (4d), the above set of reactions is progressively reversed, first causing precipitation of chromium hydroxide by the reverse of reaction (4d) and then its subsequent dissolving by the reverse of reaction (4c). 

The chromium oxides were prepared according to the following procedure [6-8]. Chromium oxide resulted from the dehydration of chromium hydroxide obtained by the addition of an ammonia solution (5M) to a solution of chromium nitrate (0.5M) The final pH was equal to 7.5 and the hydroxide formed was kept constantly stired and heated at 80°C for 1 h so as to obtain complete precipitation. This solid was filtered and washed three times with hot distilled water and dried for 16 h in an oven at 90°C. It was then submitted to a dynamic thermal treatment under nitrogen at 380°C for 8 h. The chromium oxide formed was cooled down under the same vector gas. 

Chromium hydroxide is an amphoteric compound and exhibits minimum solubility in the pH range of 7.5 to 10.0. Effluents from chromium reduction processes should be neutralized to the range of zero solubility (pH 8.5 to 9.0) to minimize the amount of soluble chromium remaining in solution. 

Another innovative flotation-filtration wastewater treatment system adopts the innovative use of the chemical ferrous sulfide (FeS), which reduces the hexavalent chromium and allows separation of chromium hydroxide, nickel hydroxide, and ferric hydroxide in one single step at pH 8.5. Figure 6.7 illustrates the entire system. Again, a DAF-filtration clarifier plays the most important role in this wastewater treatment system. 

In addition to the heavy metals stated in Table 22.10, ferro- and ferricyanide are also part of the pollutants in the wastewater generated in a chrome pigment plant. These wastes are generally combined and treated through reduction, precipitation, equalization, and neutralization to be followed by clarification and filtration processes. Most of the heavy metals are precipitated using lime or caustic soda at specific pH. Chromium is reduced by S02 to a trivalent form, wherein it is precipitated as chromium hydroxide at specific pH. Sodium bisulfide is also employed to precipitate some of the metals at a low pH. The treated water is recycled for plant use while the sludge is sent to landfills (Figure 22.7). 

None of the Cr(III) products from Equations 6 or 7 are effective crosslinkers since a chromic aqua ion must be hydrolyzed first to form olated Cr to become reactive. Colloidal and solid chromium hydroxides react very slowly with ligands. In many gelation studies, this critical condition was not controlled. Therefore, both slow gelation times and low Cr(VI) Cr(III) conversion at high chromate and reductant concentrations were reported (9,10). 

If the metallisable dye is insoluble in water, a miscible solvent such as ethanol or ethylene glycol may be added. Polar solvents such as formamide or molten urea have sometimes been preferred. It is likely that such solvents will preferentially displace water molecules and coordinate with the chromium (III) ion as the first step in the reaction. If colourless organic chelates of chromium, such as those derived from oxalic or tartaric acid, are used instead of or in addition to hydrated chromium (III) salts, the difficulty of replacing the strongly coordinated water molecules in the first stage of the reaction is eliminated. In this way the initial reaction can be carried out at high pH without contamination by the precipitation of chromium hydroxide. Use of the complex ammonium chromisalicylate (5.12) in this connection should also be noted (section 5.4-1). 

The chromium and nickel are identified as chromium hydroxide and nickel (HI) oxide, respectively. 

Change in Composition of Surface Film with Treatment. Since trivalent chromium hydroxide can be generally expressed as Cr203 nH20, the composition of the outermost surface layer is assumed to be expressed by "Equation 2" and the hydration degree n and covering rate a of chromium... 

The covering rate a and hydration degree n of chromium hydroxide and the polar group ratio [C ](>o / ]total shown in Fig. 8. It is found... 

During prebaking for the internal coating, dehydration of chromium hydroxide (decrease in n-value) has occurred. If surface oil is oxidized at the same time, the adhesion loss of UVC lacquer due to the dehydration is made up for by the oxidation of the oil. 

The adhesion of UVC lacquer is likely to deteriorate in wicket-contact portions where the dehydration of chromium hydroxide occurs but only limited oxidation and vaporization of oil take place. 

Johnson, J.E. Matijevic, E. (1992) Interactions of proteins with uniform colloidal hematite and chromium hydroxide particles. II. Stability and mobility. Colloid Polymer Sd. 270 364-369... 

Chromium(III) chloride hexahydrate may be prepared by treating chromium hydroxide with hydrochloric acid ... 

The compound may be prepared by the reaction of chromium hydroxide with hydrofluoric acid ... 

Chromate, dichromate, permanganate, chlorate and hypochlorite and other oxidants are readily reduced hy hydrazine for example, removal of chromate from wastewater may he achieved fuUy hy converting water-soluhle chromate to insoluble precipitate of chromium hydroxide, Cr(OH)3 ... 

The formation of rnonodisperse amorphous, spherical particles of chromium hydroxide is offered here as an example. These dispersions are readily obtained by simply heating chrome alum solutions (35). It was established experimentally that the sulfate ion was essential in order to obtain uniform dispersions thus, when chromium nitrate solutions were aged, monodispersed particles were produced only if a sulfate salt was introduced into the reaction. 

Fig. 1.1.7 Complex solutes present in solutions of chrome alum, which on aging yield monodispersed amphorous spherical chromium hydroxide panicles. A labeled solution initially 4.0 X 10 4 mol dm-3 in chrome alum was heated at 75°C for 9 days. After cooling and filtering off the particles, the filtrate was subjected to paper electrophoresis. The corresponding solutes are (A) Cr1+, (B) Cr,(0H)2S042+. (C) Cr(OH)2, (D) Cr(0H)S04 and Cr(OH).,. (From Ref. 36.)...

It is noteworthy that reversing the charge on such particles from positive to negative by increasing the pH with a base does not affect the size distribution of the particles, as documented in the example of chromium hydroxide (51). 

Figure 1.1.19 illustrates such hematite particles coated with chromium hydroxide in which the latter was produced by the hydrolysis of a chrome alum solution in the presence of a-Fe203 cores on aging the dispersion at 85°C. For greater efficiency the chromium salt solution was either preheated or preheated with KOH (but avoiding precipitation of chromium hydroxide) (144). 

Preparation and Properties of Chromium(III) Hydroxide. Prepare chromium hydroxide and see how it reacts with dilute solutions of acids and alkalies. Write the equations of the reactions. What type of hydroxides does chromium hydroxide relate to What is the structure of the hydroxochromate(III) ion ... 

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