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The vertical position of the pulp-froth interface in a flotation cell is an important parameter in froth flotation processes which needs to be controlled in situ. For this purpose, we introduce the ultrasound transit time technique (UTTT), a non-invasive technique for detecting and measuring the position of this interface. Based on lab-scale experiments, the method is evaluated for a pulp-air and a pulp-froth interface. The technique was found to be well applicable in pulp with up to 21% particle mass fraction. In a container with 80 mm height the accuracy is found to equal 1mm.

The vertical position of the pulp-froth interface in a flotation cell is an important parameter in froth flotation processes which needs to be controlled in situ. For this purpose, we introduce the ultrasound transit time technique (UTTT), a non-invasive technique for detecting and measuring the position of this interface. Based on lab-scale experiments, the method is evaluated for a pulp-air and a pulp-froth interface. The technique was found to be well applicable in pulp with up to 21% particle mass fraction. In a container with 80 mm height the accuracy is found to equal 1mm.

In a flotation cell, turbulence influences the motion of solid particles relative to the bubble surface, and, thus, affects the recovery rate. But, the impact of turbulence on the probability of a bubble-particle aggregation is still difficult to measure, especially in a dense flow. Therefore, the focus of this work was to apply PEPT as a method to investigate the effect of turbulence on the particle movement and bubble-particle interaction in an opaque flow. Single air bubbles (db=2.5 mm) were generated on a needle in a water flow channel. Upstream, a grid produced an isotropic turbulent flow with 5% to 15% turbulence intensity and a Kolmogorov microscale of 20µm. Depending on the distance to the grid, the flow near the captive bubble (Reb~450) was characterized by eddies of different length scales and magnitude with tomographic PIV. The solid suspension contained up to 0.3% PMMA particles (dp=200-400µm) and up to six radiolabelled particles (dp=300-400µm) coated with PMMA. The trajectories of the labelled particles were used to determine the average particle distribution in the turbulent field and describe the bubble-particle interactions. These results provide valuable information on the applicability of PEPT in turbulent and dense flow fields as well as on particle trajectories close to bubbles, enhancing our understanding of key flotation phenomena.

In a flotation cell, turbulence influences the motion of solid particles relative to the bubble surface, and, thus, affects the recovery rate. But, the impact of turbulence on the probability of a bubble-particle aggregation is still difficult to measure, especially in a dense flow. Therefore, the focus of this work was to apply PEPT as a method to investigate the effect of turbulence on the particle movement and bubble-particle interaction in an opaque flow. Single air bubbles (db=2.5 mm) were generated on a needle in a water flow channel. Upstream, a grid produced an isotropic turbulent flow with 5% to 15% turbulence intensity and a Kolmogorov microscale of 20µm. Depending on the distance to the grid, the flow near the captive bubble (Reb~450) was characterized by eddies of different length scales and magnitude with tomographic PIV. The solid suspension contained up to 0.3% PMMA particles (dp=200-400µm) and up to six radiolabelled particles (dp=300-400µm) coated with PMMA. The trajectories of the labelled particles were used to determine the average particle distribution in the turbulent field and describe the bubble-particle interactions. These results provide valuable information on the applicability of PEPT in turbulent and dense flow fields as well as on particle trajectories close to bubbles, enhancing our understanding of key flotation phenomena.

The position of the pulp-froth interface in a flotation cell is an important parameter in froth flotation processes which needs to be controlled in situ. For this purpose, we employ a non-invasive technique, the so called ultrasound transit time technique (UTTT). In UTTT, a transducer sends Ultrasound pulses of several MHz through the pulp. The pulses are reflected at the pulp-froth interface. The echoes are recorded by the emitting transducer and the time-of-flight is computed. The vertical position of this interface is calculated by multiplying the time-of-flight with the speed of sound of the pulp. The latter is determined simultaneously by a second transducer, using a target plate which is placed at a known height in the pulp, simultaneously. Based on detailed measurements, the capabilities of the method are evaluated for a pulp-air and a pulp-froth interface in a lab-scale setup. The accuracy is found to be equal to better than 3%.

In a flotation cell, turbulence significantly affects the recovery rate. Microturbulence influences the motion of solid particles and thus, the probability of bubble-particle aggregation. We investigated the effect of microturbulence on bubble-particle interactions with positron emission particle tracking (PEPT). Single air bubbles (db=2.5mm) were captured generated on a needle in a water flow channel. Upstream, a mesh produced an isotropic turbulent flow with 5-15% turbulence intensity. Depending on the distance to the grid, the incident flow near the captive bubble (Re=600) was characterized by eddies of different length scales and magnitude. The liquid contained up to 0.3% PMMA particles (dp=200-400µm) and up to six radiolabelled particles coated with PMMA (dp=300-400µm). The trajectories of the labelled particles were recorded, allowing us to determine the average particle distribution in the turbulent field and describe the bubble-particle interactions. These results provide valuable information to enhance our understanding of key flotation phenomena.

In a flotation cell, turbulence significantly affects the recovery rate. Microturbulence influences the motion of solid particles and thus, the probability of bubble-particle aggregation. We investigated the effect of microturbulence on bubble-particle interactions with positron emission particle tracking (PEPT). Single air bubbles (db=2.5mm) were captured generated on a needle in a water flow channel. Upstream, a mesh produced an isotropic turbulent flow with 5-15% turbulence intensity. Depending on the distance to the grid, the incident flow near the captive bubble (Re=600) was characterized by eddies of different length scales and magnitude. The liquid contained up to 0.3% PMMA particles (dp=200-400µm) and up to six radiolabelled particles coated with PMMA (dp=300-400µm). The trajectories of the labelled particles were recorded, allowing us to determine the average particle distribution in the turbulent field and describe the bubble-particle interactions. These results provide valuable information to enhance our understanding of key flotation phenomena.

The position of the pulp-froth interface in a flotation cell is an important parameter in froth flotation processes which needs to be controlled in situ. For this purpose, we employ a non-invasive technique, the so called ultrasound transit time technique (UTTT). In UTTT, a transducer sends Ultrasound pulses of several MHz through the pulp. The pulses are reflected at the pulp-froth interface. The echoes are recorded by the emitting transducer and the time-of-flight is computed. The vertical position of this interface is calculated by multiplying the time-of-flight with the speed of sound of the pulp. The latter is determined simultaneously by a second transducer, using a target plate which is placed at a known height in the pulp, simultaneously. Based on detailed measurements, the capabilities of the method are evaluated for a pulp-air and a pulp-froth interface in a lab-scale setup. The accuracy is found to be equal to better than 3%.