Dyestuff adsorption

To correlate experiments on dyestuff adsorption and exchange on the surface of a lead chromate precipitate. 

A number of papers have appeared on the removal of heavy metals in the effluents of dyestuff and textile mill plants. The methods used were coagulation (320—324), polymeric adsorption (325), ultrafiltration (326,327), carbon adsorption (328,329), electrochemical (330), and incineration and landfiU (331). Of interest is the removal of these heavy metals, especiaUy copper by chelation using trimercaptotria2ine (332) and reactive dyed jute or sawdust (333). 

A disadvantage of adsorption indicators is that silver halides are sensitised to the action of light by a layer of adsorbed dyestuff. For this reason, titrations should be carried out with a minimum exposure to sunlight. When using adsorption indicators, only 2 x 10-4 to 3 x 10 3 mol of dye per mol of silver halide is added this small concentration is used so that an appreciable fraction of the added indicator is actually adsorbed on the precipitate. 

Other dyestuffs have been recommended as adsorption indicators for the titration of halides and other ions. Thus cyanide ion may be titrated with standard silver nitrate solution using diphenylcarbazide as adsorption indicator (see Section 10.44) the precipitate is pale violet at the end point. A selection of adsorption indicators, their properties and uses, is given in Table 10.8. 

Pagga U, Taeger K (1994) Development of a method for adsorption of dyestuffs on activated sludge. Wat Res 28 1051-1057... 

The practical characteristic of a dyestuff is that when a textile is immersed in a solution containing a dye. the dye preferentially adsorbs onto and diffuses into the texiile. The thermodynamic equations defining this process have been reviewed in detail. The driving force for this adsorption process is the difference in chemical potential between the dye In the solution phase and the dye in the fiber phase. In practice it is only necessary to consider changes in chemical potential and to understand that the driving force is the reduction in free energy associated with the dye molecule moving from one phase to the other, as the molecule always moves to the siate of lowest chemical potential. 

There is often considerable specificity in adsorption, one of two fairly closely related dyestuffs being adsorbed, the other not. This is to be expected on the theory that a close correspondence of atomic spacings is required. The specificity is of interest as providing a rather simple parallel to the specific adsorptions on complex biological surfaces such as bacterial cell walls or enzymes (see 17).1... 

Gibby and Argument,1 continuing measurements of the adsorption of dyestuffs at liquid interfaces, by a method similar to that used first by Donnan (see p. 113), find that very often the adsorption is considerable at very low concentrations, but decreases at somewhat higher, though still fairly low, concentrations. The experimentally measured adsorption does not usually decrease nearly so much as that calculated from the... 

Preceding measurements by Swidersky on the same dyes were carried out with the static method [7, 8, 9, 14]. The differences between the measurements result from an incomplete purification of the same sample during preceding investigations. Recent experiments on purer dyes using the same static method agree very well with the measurements according to the dynamic method [15]. An adsorption effect of the stationary phase that has been used to precipitate the dyestuff on its surface is not found within the experimental accuracy. 

In the presence of anions which are precipitated by calcium chloride solution, proceed as follows. Precipitate the acetic acid test solution with calcium chloride solution, and collect the precipitate on a filter or in a centrifuge tube. Remove the water from the precipitate either by drying or by washing with alcohol and ether. Mix a small amount of the precipitate with diphenylamine in a dry micro test-tube, add a little concentrated phosphoric acid, and heat gently over a free flame. Calcium phosphate and free oxalic acid are formed, and the latter condenses with the diphenylamine to aniline blue and colours the hot phosphoric acid blue. The colour disappears on cooling. Dissolve the melt in alcohol, when a blue colouration appears. Pour the alcoholic solution into water thus precipitating the excess of diphenylamine, which is coloured light blue by the adsorption of the dyestuff. The dye may be extracted from aqueous solution by ether. 

Adsorption of Several Days on Starches of Various Origins796 Amount of Dyestuff Adsorbed, %... 

Ozoh, P. T. E. (1997). Adsorption of cotton fabric dyestuff waste water on Nigeria agricultural semi-activated carbon. Environ. Monitoring Assessment. 46, 3, 255-265. 

B. Chem, C. W. Hui and G. Mckay, Film-pore diffusion modeling and contact time optimization for the adsorption of dyestuffs on pith, Chem. Eng. J., 84, 77-94,2001. 

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