Image Analysis of Alum Coagulated Mineral Suspensions

Abstract Four different mineral suspensions were coagulated in order to determine whether the geometric characteristics of flocs formed would vary with the composition of aggregating particles. Minerals chosen for the experiment were materials commonly found in Lake Ontario bottom sediments. The settling velocities along with the sizes of the coagulated flocs were measured in a quiescent water column by a multiexposure photography technique. The computerized image analysis system BIOQUANT IV was applied for the determination of the following physical characteristics of aluminium coagulation flocs: cross-sectional area, longest dimension, perimeter, shape factor, equivalent circular diameter and settling velocity. The settling rates of the four types of studied flocs varied significantly. Temperature and pH variations may have had a significant effect on sizes of formed flocs. Fractal dimensions were different for the four sets of flocs, and the differences could not be explained by the various surface charge (stickiness) of aggregating particles. The properties of aggregating particles could be considered as one of the factors influencing some physical characteristics of aggregates formed in water. Keywords: water coagulationalum flocsimage analysissettling velocitiesmineral suspensions