8. Zeta Potential and Particle Size Characteristics of Red Mud Waste

Neutralization is essential for high alkaline wastes like red mud for its effective utilization. As such, the process of neutralization involves treating the red mud with either chemicals or other waste materials. Among several factors that affect the efficiency of the treatment, surface charge characteristics and particle diameter parameters predominantly influence the performance of the neutralization. The present study focuses on examining the surface charge properties which include flocculation and dispersion and determining the particle size characteristics which include mean particle diameter under variable pH conditions. Surface charge properties are interpreted from zeta potential, ζ, measurements made on suspensions prepared with red mud waste at different pH values. The average particle diameter is obtained from the grain size analysis established on the same suspensions using the zeta potential analyser. Results indicate that the zeta potential increases with pH up to a certain pH value of 4 and then begin to fall with the further increase in pH. The zeta potential turned into negative (up to a maximum value of −48 mV) at pH value of 6.6, which denotes the point of zero charge for the red mud, from the initial positive (from a maximum of +41.8 mV) value. However, the value becomes stabilized when the pH is 10 and above. An average particle diameter of (a) 65–150 nm at pH of 3.96 and above 9.00, indicating a complete dispersed state of the grains, and (b) 1660 nm, 2176 nm and 1080 nm at pH of 1.15, PZC (i.e. pH of 6.6) and pH of 7.48, respectively, indicating likely agglomeration of the grains, was recorded with the change in pH of the suspension. The study finds that the waste possesses surface charge characteristics, which appear to be greatly influenced by the pH.