Agglomeration binding mechanisms

Binders are frequently used to assist in the agglomeration process. They make a difference in the performance of the end product. Gantner (2003) pointed out that there are six types of binding mechanisms ... 

Agglomeration of only one component of a mixture controlled by, for example, binding mechanism, binder, particle size see also Oil agglomeration). 

See Binding mechanism (Section 2.2). Technique involving induration of green agglomerate by heat. Generally, bonding at a temperature below the melting point of the main constituent by application of heat. 

The binding mechanisms of size enlargement by agglomeration were first defined and classified by Rumpf. According to Table 3 they are divided into five major groups, I to V, and several subgroups. 

An important group of binding mechanisms of agglomeration is characterized by the formation of binder bridges at the coordination points between the... 

In addition to these four typical binding mechanisms (Figure 14a to d), whereby bonding occurs at the coordination points, three other models exist. Form-closed bonds (e) are only possible if the particulate matter is shaped such that, somehow, it can interlock and capillary forces (f) can only become effective in a disperse system which is filled with a liquid that forms concave menisci at the pore ends. In the third case, particles forming the agglomerate are embedded in a matrix of binder the model can also be depicted by Figure 14(f) where the dark areas represent the binder matrix. 

Figure 15. Classification of the phenomena of binding mechanisms of agglomeration...

Because of the field character of this binding mechanism, the tensile strength is independent of the particle size. Also, the strength due to excess charges is very small and the charges tend to equalize with time. Therefore, this mechanism is most often only significant for the initial formation of agglomerates. 

Particle shape is of the greatest importance for agglomeration. Typical characteristics are particle roundness or the general overall shape and surface roughness. For some binding mechanisms and/or agglomeration methods, the particle shape is the most decisive particle characteristic. 

In some cases, for example, toxic characteristics of the material may prohibit shipment of test quantities to vendors laboratories and/or contamination of laboratory buildings and equipment may be irreversible. In other cases, particularly in hot agglomeration, the material must be tested in statu nascendi because cooling and reheating a sample after shipment does not recreate the original material characteristics and the actual binding mechanisms. In those cases, construction of a pilot plant on the project site or other suitable location must be considered which may be equipped with purchased or rented machinery. If this solution is selected, the above remarks on scale-up must still be kept in mind. 

The binding mechanisms between powder particles are applied to build agglomerates with specific product characteristics. The two most widely used agglomeration processes are tumble and pressure agglomeration. The latter also includes pelleting . In this book, all other agglomeration techniques will be covered under other processes . 

The major growth mechanisms in suspended solids agglomerators are layering and coalescence after collision of wetted particles with each other or of particulate solids with binder droplets. At the same time drying or cooling takes place to activate the permanent binding mechanism (solid bridges). Intensive contact of... 

In pressure agglomeration a more or less stationary bed of particles is consolidated by pressure, bringing about various binding mechanisms. 

Therefore, the basis for all agglomeration methods can be found in the availability and/or selection of binding mechanisms. The technique or equipment used is only the vehicle to obtain the agglomerated product of desired shape, size, strength, density, etc. Consequently, agglomeration methods that can be considered special still employ similar effects and mechanisms, as mentioned before in the two main groups tumble (Section 4.2.1) and pressure (Section 4.2.2)... 

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