Influence of anticaking agents on the caking of sodium chloride at the powder and two-crystal scale

•Caking strength of NaCl crystals is measured at powder and two-crystal scales.•Ferrocyanide and ferricyanide are excellent anticaking agents at both scales.•Iron(III) meso-tartrate works only at the powder scale as an anticaking agent.•Higher dosages of anticaking agents are needed at the two-crystal scale.•Caking strength is determined by the number of contact points between crystals.

The effectivity of the anticaking agents ferrocyanide, ferricyanide and iron(III) meso-tartrate on the caking of sodium chloride was studied at the powder scale and on a two-crystal scale. Using the integrated stirring energy as a measure of caking strength of the powders gives results that agree well with industrial experience with these anticaking agents. For two single crystals, the required separation force was used as a measure for the caking strength. In this case, higher dosages of anticaking agents are required to prevent caking. This is caused by an increase in the number of contact points between the crystals, as was concluded from the surface morphology of the sodium chloride crystals, which we studied using atomic force microscopy. This change of the surface morphology is in turn caused by the applied anticaking agents. This shows that it is not only the surface area, but also the number of contact points, and thus the particle size distribution, which are critical in determining the optimal dosage of anticaking agents on caking powders.

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