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

Abstract

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 measurements 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 backscattering coefficient b on the foam’s liquid fraction ϕ, we developed a model to calculate b from the echo signal. Local backscattering coefficients b n {b_{n}} can be determined for time gated windows and show a trend in the dependency on the foam’s liquid fraction ϕ (for ϕ < 0.8 \phi <0.8 %). The absolute uncertainty of the liquid fraction determined by means of an electrical reference measurement is σ ϕ = 0.079 {\sigma _{\phi }}=0.079 %. We demonstrated the capability of spatio-temporally resolved measurements with a frame rate of 0.33 Hz and an axial resolution of 7.9 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.

Minimal‐Invasive Method for the Evaluation of Liquid Fractions in Foams with a Point Level Sensor

“…Leon Knu ¨pfer 3 Sascha Heitkam Recently, a method based on ultrasound was proposed [15]. But its applicability still has to be assessed in industrial processes.…”

“…Therefore, the wall material and the immersion depth (ImD) had to be kept constant to ImD = 20 mm during different experiments. Electrical conductivity measurements were achieved using a pair of wall-mounted electrodes and a custom-made measurement setup [15]. The liquid fraction j was then determined by using the well-established Eq.…”