Agglomeration techniques

A most useful feature of the agglomeration technique is its ability to work with extreme fines. Even particles of less than nanometer size (ca 10 ° m) can be treated, if appropriate, so that ultrafine grinding can be appHed to materials with extreme impurity dissernination to allow recovery of agglomerates of higher purity. A number of appHcations of Hquid-phase agglomeration have reached either the commercial or semicommercial pilot scale of operation. 

The partial agglomeration technique has been described in detail elsewhere (15). The colloidal stability of the dispersed polymer particles is not destroyed in the partial agglomeration process. The agglomeration step involves treatment of the dispersed rubber particles at a stage where they have no outer protective layer of non-rubbery, i.e., rigid polymer to prevent the massive or complete coalescence of the rubber particles (13). 

Figure 12.14. Common shapes and sizes of pellets made by some agglomeration techniques, (a) Sizes and shapes of briquets made on roll-type machines, (b) Catalyst pellets made primarily by extrusion and cutting (Imperial Chemical Industries), (c) Some of the shapes made with tabletting machines.

Physical cleaning of various coals by oil agglomeration reduced levels of As, Cr, Pb, Mn, Mo, Ni, and V by 50-80%, while levels of some other trace elements were reduced by lesser amounts (20). Oil agglomeration appeared to be more effective at removing trace elements than the wet concentrating table or float/sink density separations. This may be related to an increase in the liberation of mineral matter associated with grinding to produce the relatively fine particle sizes required in the oil agglomeration technique. 

In the second group of mixer agglomeration techniques, powders are moistened to a much lesser extent than the wet capillary state. Relatively weak powder clusters are formed. An example is the moistening, equilibration, drying and cooling sequence used to produce instantized food products. 

In these agglomeration techniques, many operating parameters are used to improve the quality of the process a non-exhaustive list reads like ... 

Pietsch, W.B. Agglomeration Techniques for the Manufacturing of Granular Materials with Specific Product Charac- 29. 

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 . 

In spite of the inherent limitations of all growth agglomeration techniques, which are also valid for discs, the latter piece of equipment has attracted considerable interest during the short time since it was first introduced. Reasons for this are the unusually good and easy control of the performance of the apparatus and the uniform product size and shape that can be obtained. To further improve these conditions a number of modified disc configurations have been proposed and some are being used to achieve special effects. 

These variations are present in products from all pressure agglomeration techniques and lead to a weakening of the compact. If a sintering step follows, distortion is possible due to differences in the amount of contraction occurring at the positions of different density (see also sections 4.2.2.3.5 and 4.2.2.5). 

To render materials suitable for pelleting or extrusion, they must have inherent binding characteristics or contain binders and feature a certain lubricity. Therefore, most medium pressure agglomeration techniques use moist mixtures which are prepared in a mixing step prior to pelleting. 

In the early 1950s another pressure agglomeration technique emerged as an alternative to the already conventional tumble agglomeration methods in mixers, drums, pans, and suspended solids granulators. This technology uses roller presses which can be easily adapted to a wide range of capacities and materials. 

In the context of this subject three major agglomeration techniques, each with a variety of equipment choices, can be distinguished ... 

At about the same time, another agglomeration technique was in its first development stages in North America pelletizing of fine iron ore concentrates. Within two decades this technology became a multimillion ton per year industry on a worldwide scale (see Section 5.4.2). 

Therefore, it was the author s intent to cover—for the first time in a textbook on agglomeration—the fundamentals in considerable detail and to introduce the multitude of agglomeration techniques as well as applications that have been developed during the past 100 years and, more specifically, during the most recent four to five decades. In Chapter 4 (Industrial Size Enlargement Equipment and Processes) as well as Chapter 5 ([Some Selected] Industrial Applications of Agglomeration) pressure agglomeration and, explicitly, roller presses have been covered in particular detail because of the author s past and present involvement as an expert in this area. 

Majid, A., and Argue, S. (2001). Remediation of heavy metal contaminated solid wastes using agglomeration techniques. Miner. Eng. 14(11), 1513-1525. 

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