The mining and processing industry is committed to a zero waste approach, which includes minimizing particulate emissions. One challenge involves the shipping and handling of bulk commodities, ranging from coal and iron ore to limestone and bentonite. These types of bulk granular materials can break down and abrade during handling and discharge, producing particle fragments of a wide range of sizes. Certain particle sizes can be airborne and are undesirable for a variety of reasons. Commercial iron ore pellets are also susceptible to cracking and abrasion during shipping and handling, resulting in the formation of undesirable fines and dust. Manufacturers characterize the attrition resistance of their pellets using an abrasion index (AI) to indicate whether their products will produce acceptable or unacceptable levels of fines. Structurally weak pellets tend to produce a significant amount of fines from both impact and attrition. In pelletizing, the abrasion index is used to indicate the resistance of pellets to attrition. The abrasion index is defined according to ISO 3271 as the amount of material smaller than 0.5mm produced by the rotation of the pellets in a rotating drum. Historically, AI has been one of the main quality indicators for pellets and should therefore be as low as possible. The maximum limit for AI depends on the pellet user, but it is generally desirable that it does not exceed 5% when tested in a drum according to ISO 3271. Factors influencing pellet dustiness can range from the starting materials to agglomeration; to the solidification or heat hardening conditions; depending on the type and degree of processing – all of these can interact to some extent, influencing the final structure and properties of the granules and, ultimately, dust formation (figure).

    The use of binding additives and an increase in the specific surface area of the concentrate reduce the abrasion index. However, the use of organic binders leads to higher abrasion indices compared to pellets on a bentonite binder. Pellets obtained on conveyor firing machines have a higher abrasion index due to uneven firing along the height of the pellet layer. Granules from the lower layer have many fragile pellets, leading to an increase in the abrasion index compared to pellets of the middle and upper layers fired at higher temperatures with a longer time interval. 

       For example, when the firing temperature was reduced from 1280 C in the upper part of the layer to 1200 C at the layer-bed boundary, the abrasion index increased from 3.7% to 11.9%. Insufficient firing is the main reason for the formation of fine particles and dust. Each type of batch has its own critical firing temperature required to achieve good solidification of the granules. The quality of pellets is very sensitive to temperatures below the critical temperature. The lower the firing temperature, the longer the time interval required for pellet processing. It has been found that larger pellets in the lower layer are insufficiently fired, and increasing pellet diameter requires longer firing times for complete solidification. Consequently, pellets produced in SG have a higher proportion of insufficiently fired pellets, resulting in a higher level of fines. In GK, all pellets are fired at high temperatures, so the pellets are sintered to a more uniform level. Granules are formed from powder material and easily disintegrate into individual particles and weakly bonded fragments if the solidification process and the phenomena associated with it (oxidation and recrystallization, melt formation, reduction in pore size and porosity, and grain growth) are not complete. The physical principles for the formation of the abrasion resistance index are based on two factors: shape (degree of surface roughness) and the degree of sintering of the particles located in the surface layer of the pellet. The surface condition ultimately determines the formation of fines during mutual contact of pellets. Pellets of class +5-8mm have the greatest abrasion due to a larger contact surface with each other and a greater friction force. Pellets in the class range of 11.0-12.5mm have the minimum abrasion. With an increase in the basicity modulus of granules and the addition of solid fuel to the charge, the abrasion index increases due to an increase in pellet porosity and a change in the pellet microstructure.                  Pellets are decomposed as a result of impacts and abrasion during their production and handling. Depending on the type (impact or abrasion) and degree of destruction, different amounts of finely dispersed material are formed. When destroyed by impact (when falling from different heights at handling units, loading and warehousing), the destroyed  granules are distributed in the range of particle size class from 0.5mm to 16mm, when destroyed by abrasion (during transportation due to friction of granules between themselves), the resulting material is distributed in the range of size class 0-0.5mm and is the main source of dusting and material losses, including emissions into the environment.