In this work an ultrasound-based measurement method is used for monitoring suspension velocity and build-up of magnetic material inside a wet low-intensity magnetic separator, a process used e.g. in beneficiation of magnetite ores. Today the only available option is to monitor material transport between unit operations; i.e. flow rate, solids concentration, and particle size distribution of suspension flow in pipes are measured online using standard equipment. An acoustic backscatter system is fitted to the tank of a separator, and used to monitor the internal flow. A method called ultrasonic velocity profiling is used to capture internal velocity profiles. Simultaneously, the backscatter signal intensity is used to get indications about local solids concentration of the flow, and build-up of magnetic material. The methods are evaluated in realistic conditions, where the effect of varying factors relevant to machine performance is investigated. The included factors are; the slurry feed rate, the slurry solids concentration, the magnet assembly angle, and the drum rotational speed. The presented method gives useful information about the internal material flow inside the separator. The velocity measurements capture the, sometimes complex, internal flow patterns, for example the presence and velocity of a recirculating flow in the dewatering zone. Additionally, keeping a balanced material loading in the concentrate dewatering zone is important to separator performance. Using the signal backscatter intensity it is possible to qualitatively monitor this material loading. Generally these direct measurements can aid in improvements to machine design, process optimization, and process control. (C) 2015 Elsevier Ltd. All rights reserved.