Linear, spatio-temporally resolved ultrasound measurement of the liquid fraction distribution in froth

Froth flotation is an important process for separating metal particles from gangue. A single flotation circuit for copper uses approx. 44 billion litres water a year. In situ process monitoring of the foam’s parameters and closed-loop control can reduce the resource use. However, no measurement technique is broadly employed that yields the liquid fraction distribution in the froth. Optical measurement are prevented by the bulk foam’s opacity. Though, ultrasound in the low frequency range is able to penetrate froth. In this paper we investigate the application of ultrasound to measure the local liquid content of aqueous foam in the axis of the ultrasound beam. Assuming a dependency of the reflection coefficient 𝑟 on the foam’s liquid fraction 𝜑, we developed a model to calculate 𝑟 from the reflected signal. Local reflection coefficients 𝑟_𝑛 can be determined for timegated windows and show a monotonic dependency on the foam’s liquid fraction 𝜑 (for 𝜑< 0.8 %). The uncertainty of the liquid fraction determined by means of a electrical reference measurement is 𝜎_𝜑= 0.079%. We demonstrated the capability of spatio-temporally resolved measurements with a frame rate of 3 s and an axial resolution of 0.79 mm in an experiment with a time-varying, inhomogeneous liquid fraction. This research work is contributing to a determination of in situ information of the foam’s parameter in a flotation process.