Agglomeration density

Bulk density is easily measured from the volume occupied by the bulk solid and is a strong func tion of sample preparation. True density is measured by standard techniques using liquid or gas picnometry Apparent (agglomerate) density is difficult to measure directly. Hink-ley et al. [Int. ]. Min. Proc., 41, 53-69 (1994)] describe a method for measuring the apparent density of wet granules by kerosene displacement. Agglomerate density may also be inferred from direcl measurement of true density and porosity using Eq. (20-42). 

Mean particle size Hard agglomerates Density Voids... 

The addition of fines to a powder system allows a larger top size of particle to be agglomerated due to the attendant increase in cohesive forces caused by a decrease in surface mean particle diameter and increase in agglomerate density. Thus, although eqn. (1) indicates a top size of about 150 pm for monosized particles with aqueous binders, the top size of feed for industrial disc pelletizers is usually higher at 30 to 50 mesh (300 to 600 /zm) with the provision that at least 25% should be finer than 200 mesh (75 /zm) [7]. Other liquids with surface tensions lower than that of water, or liquid/ solid systems in which the particle surface is imperfectly wetted, require finer particle sizes to make successful balling possible. 

By Eq. 2 and D = 2.5 from DLA we estimate the apparent density of the aggregate to be 700 g 1 . This is the density found experimentally, when powdered fumed silica is pressed to a solid disc. > = 2.1 from RLCA then gives an agglomerate density of about 20 g 1 - close to the bulk density of the freshly produced fluffy product. 

Porosity and Density There are three important densities of granular or agglomeratecf materials bulk density pt (related to the volume occupied by the bulk solid), the apparent or agglomerate density pg (related to the volume occupied by the a lomerate including internal porosity), and the true or skeletal soli% density pj. These densities are related to one another and the interagglomerate voidage ej, and the intraagglomerate porosity Eg [Eq. (21-96)]. 

Lubricants may be either liquid or solid additives (Tab. 5.3). They reduce the coefficient of friction between the particles of a bulk mass and, therefore, result in a somewhat higher agglomerate density or lower porosity, s. According to the relationship k s = K (see Section 5.2.1) additional adhesion sites (characterized by the coordination number, k) are activated by which increased agglomerate strength is expected. 

The example shows that the various suspension properties specifically reflect the degree of destabilisation. The settling velocity, which directly reflects the increase of particle size during aggregation, is not necessarily the most appropriate parameter for the detection of aggregation because it is affected by other properties as well (e.g. by the effective agglomerate density). Parameters that are sensitive to particle interaction, like sediment porosity, may serve as a useful alternative or supplement. 

D J Bell, K H Brunner. A method for the evaluation of floe break-up in centrifuges. Filtration+Separation, july/August 1983 R C Klimpel, C Dirican, R Hogg. Measurement of agglomerate density in flocculated fine particle suspensions. Particulate Sci Technol 4 (1986) 45-59 R C Klimpel, R Hogg. Evaluation of floe structures. Colloids and Surfaces 55 (1991) 279-88... 

To investigate dispersive mixing, 2 mm spheres of fluffy carbon black were moulded into model agglomerates , densities 0.3 and 0.4 gJcrcE and a device ( 2) with 10 mm cavities in both rotor and stator compared with device 1 (deep cavities). Neither were dispersed in 1 (deep cavities), nor was 0.4 in 2 (shallow cavities). However, the 0.3 density agglomerate was dispersed in 2 by tail formation and erosion as described in Chapter 14. 

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