Contact angle measurements of iron ore powders

The wettability of three iron ore powders from different sources were measu red by comparing the air pressures required to halt the capillary flow of w ater and cyclohexane up through packed beds of the powders. The calculated contact angles of the ores ranged from 30 to 70 degrees. The contact angles were compared to the chemical composition of the ores. The contact angle w as seen to increase as the ratio of oxide/oxy-hydroxide (haematite/goethite ) was increased. During these measurements, a previously unnoted problem wa s encountered. As liquid rises up the packed bed, air was forced down the w all of the column where the packing fraction is lower than in the bulk. Unl ess prevented, when this air reached the base of the column it rapidly expa nded 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 t he bed on a medium that can generate a higher capillary pressure than the p owder of interest. In this case, a thin precoat layer of fine material (dia tomaceous earth) was successfully used. (C) 2000 Elsevier Science B.V. All rights reserved.