One of the conditions for obtaining conditioned raw and fired pellets with specified physical and chemical characteristics is the organization of high-quality averaging of raw materials and obtaining a homogeneous composition of the charge. As a result of the mixing process in the mixing unit, there is a mutual movement of particles of various components, which are separate before mixing. In an ideal state after mixing, in any selected sample in the volume of the mixture, the ratio of the components must correspond to the specified ratio of the components. For example, if three components of the charge are mixed, the masses of which are related as integers a:b:c, then in any selected sample taken at an arbitrary point, the masses after ideal mixing must correspond to the values a:b:c. However, the presence of numerous factors affecting the movement and averaging of particles does not allow achieving an ideal distribution of each component in the volume of the charge. Three types of main factors affecting the quality of mixing of components can be distinguished:
         a. mixing methods (spraying, pouring, fluidized bed, layering of elements);
         b. design features of the mixer (design of the mixing device, degree of filling, speed, nature of circulation);
         c. physicochemical properties of materials (granulometric composition, ratio of components, bulk density, coefficient of                  internal friction);​​​
         For simplicity of assessing the quality of mixing materials and assessing one random variable, the mixture is conventionally considered two-component. For this purpose, one component is isolated from the mixture, which is the key one, and the remaining components are combined into the second conventional component. The quality of the resulting mixture is judged by the degree of distribution of the key component in the mass of the second conventional component.

     To calculate the degree of mixing I based on the analysis of the samples taken. various formulas are used. The most commonly used formula is:

 

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n – number of samples taken, pieces;
X1, X2 – relative concentrations of the samples taken calculated using the formula,

 

 

 

Fi, Fi0 – volume fractions of the analyzed component in the 1st sample and in the entire apparatus, respectively;

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​       Samples from the material flow at the outlet of the continuous mixer should be taken at equal and relatively short intervals. The minimum number of samples taken should be at least 20pieces, the weight of one sample taken is at least 100grams. The main method of analyzing samples of a mixture of bulk materials for the content of a key component in them is the chemical method.

      The more components of the batch are used, the more they differ in volumetric content by weight in the batch volume and the differences in their physical and chemical properties, and the better the mixing operation of all components of the batch should be organized before feeding to pelletizing for the production of green pellets in order to compensate for the chemical composition, grain size distribution, moisture, specific surface area, grain shape in the entire pellet volume. This is especially important when using organic binders or other additives that are introduced into the batch in small quantities of 50-500grams per ton of pellets in dry or liquid form. The dosage of materials before mixing must be done in the following sequence – concentrate, limestone, bentonite, additives or organic binder.

      Mixing of the charge is carried out in drum, rotary, screw, vortex or intensive mixers. If necessary, the coefficient of the degree of mixing of the charge is determined. In production conditions, this is done extremely rarely, since each installed type of mixing equipment in the process flow chart corresponds to a certain value of the coefficient of the degree of mixing of the charge (table). As can be seen from the table, the greatest homogeneity of the charge of more than 95% is provided by intensive mixers of the charge, having in their design a rotating tank for the charge and several rotating tools of swirls located in this tank. Definitely, if drum or rotary mixers are installed in the chain, they require replacement. The latest designs of mixers provide elements that allow for direct feeding of organic or other additives into them, as well as water, to regulate the humidity of the charge. High-quality mixing of materials, all other factors being equal, allows for reducing the consumption of bentonite, increasing the strength characteristics of raw pellets and reducing the yield of substandard classes for small and large fractions.