Contact angle measurements of iron ore powders

The wettability of three iron ore powders from different sources were measured by comparing the air pressures required to halt the capillary flow of water and cyclohexane up through packed beds of the powders. The calculated contact angles of the ores ranged from 30 to 70°. The contact angles were compared to the chemical composition of the ores. The contact angle was seen to increase as the ratio of oxide/oxy-hydroxide (haematite/goethite) was increased. During these measurements, a previously unnoted problem was encountered. As liquid rises up the packed bed, air was forced down the wall of the column where the packing fraction is lower than in the bulk. Unless prevented, when this air reached the base of the column it rapidly expanded and flowed into the capillary through which liquid was supplied. This cut off liquid flow into the powder bed, making it impossible to determine the contact angle. A simple method to overcome this problem is to support the bed on a medium that can generate a higher capillary pressure than the powder of interest. In this case, a thin precoat layer of fine material (diatomaceous earth) was successfully used. (C) 2000 Elsevier Science B.V.