(99e) Predicting Segregation When Materials Are Sensitive to More Than One Segregation Mechanism

Bulk materials segregate due to a variety of mechanisms. Any difference in particle scale properties can cause segregation in materials as they are subjected to flow and transport. Fines may sift down through a matrix of coarser particles, depositing below the process charge point. Angle of repose differences may cause components within the mixture to separate as they flow down a pile. Fines may also be carried by air currents, depositing where these air currents decrease. Segregation can be represented by the convection dispersion equation, provided the applicable region of convection and dispersion can be identified for each specific segregation mechanism, and the relative magnitude of segregation fluxes can be estimated for combinations of components in the mixture. This paper presents a methodology to estimate segregation fluxes, and applies this methodology to binary and tertiary mixtures. The effect of single segregation mechanisms, as well as combined mechanisms, will be examined. In addition, the effect of cohesion on each mechanism will be examined. The use of cohesion to mitigate segregation is common. However, the amount of cohesion required to mitigate segregation depends on the cause of segregation. In some cases, the addition of cohesion can induce more segregation by shifting segregation mechanisms. In other cases, the addition of cohesion helps to mitigate all segregation mechanisms. This paper examines the influence of particle scale properties on individual segregation mechanisms and on combined mechanisms. It also looks at the relationship between key bulk scale properties such as unconfined yield strength, bulk density, and internal friction on segregation potential.