Lime is a derivative of the thermal decomposition of limestone and is calcium oxide CaO or quicklime. It has a dual purpose in pellet production – it introduces CaO into the batch and simultaneously acts as a binder component of the batch. When in contact with water, quicklime is converted into slaked lime Ca(OH)2. Lime slaking is accompanied by significant heat release. The use of slaked lime as a binder component of the batch is most attractive in the production of fluxed pellets, which require the addition of several percent of CaO and/or MgO to the pellets. In traditional fluxed pellets, flux is added in the form of limestone (CaCO3) or dolomite CaMg(CO3)2, neither of which has noticeable binding properties. However, if any of these flux components are calcined to CaO or (CaO+MgO) and then hydrated and added to the granules, they can be very effective binders.

     Only slaked lime should be used for pelletizing, since adding quicklime to the batch causes it to interact with the concentrate moisture and the moisture supplied to the process to form raw pellets. The lime slaking process starts directly in the pelletizer, which completely destabilizes the process of obtaining raw pellets of the required quality and grain size. Pelletizers work with a constant batch, the presence of many small fractions and huge rolled balls with a diameter of 50mm to 200mm, it is not possible to achieve a constant grain size in the 8-16mm class. With slaked lime, the situation is somewhat different: during slaking, it disintegrates into a very fine powder and is evenly distributed throughout the mixture. Such distribution of very fine particles over the surface of the concentrate grains during moistening helps to improve the cohesive ability of the particles and the formation of raw pellets.

     The experiments confirm that slaked lime allows partial replacement of bentonite in the pelletizing batch. However, compared to the use of bentonite, the use of slaked lime in pelletizing leads to a decrease in the homogeneity of the granulometry composition and the strength characteristics of raw and, as a consequence, fired pellets. The main reason for the decrease in strength is the formation of cracks in raw and dry pellets due to the loss of plasticity. This is especially pronounced with a significant addition of slaked lime. Slaked lime used for pelletizing should be carefully averaged in the volume of the batch, the degree of lime hydration should be 100% or close to this value in order to exclude the slaking process directly in the pelletizer. Addition of calcium hydroxide reduces the effectiveness of bentonite as a binding additive due to the replacement of the more effective sodium ion (Na) with the calcium ion (Ca ) in the bentonite structure, turning it into a more calcium and less effective component of the batch, which leads to deterioration of the pellet properties. In addition, complete or partial replacement of bentonite with slaked lime additionally reduces the shock temperature when heating pellets in the firing machine. This forces the temperature regimes in the furnace of the firing machine to be rebuilt to more gentle ones, which leads to a decrease in the plant productivity by 8-10%. If we consider the binding capacity of bentonite and slaked lime, then in order for raw pellets using slaked lime as a binder to have similar strength when falling and compressing, as well as resistance to thermal shock, the dosage of slaked lime should significantly exceed the consumption of bentonite (for example, an addition of 0.5% of bentonite to the batch should correspond to a 2.0% addition of slaked lime). For these reasons, pelletizing plants do not have lime production units, its slaking and introduction into the batch, and imported lime significantly increases the costs of pelletizing. Moreover, the increased requirements for the quality characteristics of pellets by consumers make its use increasingly problematic and ineffective.