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This study investigates factors affecting the Blaine number, including type, shape, and size distribution of the grains, d80 effect, and retention time of materials in the mill. Samples were taken from different locations in production lines of the Golgohar and Chadormalu plants in Iran. For iron minerals, Davis tube tests were performed in four stages to assess the functionality of the magnetic separator to ensure matching conditions between the plant and laboratory. The Blaine air permeability system was used to analyze the Blain number. Results indicated that the samples with the same d80 but different grain size distributions had different Blaine numbers. More specifically, increasing the percentage of grains finer than 45 microns resulted in higher Blaine numbers. Moreover, in the Golgohar Hematite and desulfurization plant, the grain size distribution was relatively fixed, and minor variations in the percentages of grains finer than 45 microns led to a change in the Blaine number, and this was consistent between different days. During the concentrate production processes, higher grades of iron concentrate and lower grades of non-iron minerals were associated with lower Blaine numbers, which could be explained by the removal of iron-free minerals finer than 45 microns, including clay. Moreover, a 1% reduction in the clay minerals led to a 400-unit reduction in the Blaine number. Several samples of hematite concentrate and clay minerals with the same grain size distribution were analyzed to investigate the influence of density and the shape of grains on the Blaine number of magnetite concentrate. Here, compared to magnetite and hematite with irregular shapes, plate-shaped clay minerals showed higher Blaine numbers. Moreover, when the feed of the magnetic separator was grinded, the reduction in the grain size increased the Blaine number. In the Chadormalu plant, a retention time of 4.5 minutes in the mill was associated with the highest Blaine number as well as the least recovery of phosphorous minerals.

The determination of grain size distribution in alluvial channels plays a crucial role in understanding fluvial dynamics and processes (e.g., hydraulic resistance, sediment transport and erosion, and habitat suitability). However, to determine an accurate distribution, tremendous field efforts are often required. Traditionally, the grain size distribution of channel beds have been obtained by manually counting a set of randomly selected stones (the “pebble count”). Based on this elementary principle, many authors have proposed different adaptations to overcome weaknesses and problems with the original method; with the development of digital technology, photographic methods have been developed in order to significantly reduce the time spent in the field. Two of these “image-assisted” methods include Automated Grain Sizing, AGS, and Manual Photo Sieving, MPS. In this study, AGS and MPS were applied under ideal laboratory conditions, to be used as reference, and in two field conditions with different degrees of difficulty in terms of visual determination of the grain size distribution; these included an artificial unlined channel and two natural mountainous streams. The results were compared with those obtained with the pebble-count method. In general, strong agreement between the methods was found when they were applied under favorable conditions (”the laboratory”), and the differences between the image-assisted and pebble count methods were similar to those found in previous studies. Despite being more time consuming, MPS was deemed preferable to AGS when conditions are not optimal; in these cases, the time spent on image elaboration significantly increased in the AGS method (approximately three-fold), but the estimation error of the median grain size decreased by approximately 37%. The use of image-assisted analysis has proven to be robust for characterizing sediment in watercourse beds and reducing fieldwork time, but because field conditions can significantly affect the accuracy of results, the method choice must be carefully considered. [ABSTRACT FROM AUTHOR]