Accurate, fully automated determination of the initial settling rate of flocculated suspensions

Abstract

Abstract Thickening as the most widely applied dewatering technique in the coal and mineral processing industry involves the rapid settling of flocculated suspensions of fine tailings particles to produce a compact phase of solid at the bottom and a clear phase of liquid on the top. The mudline separating the two phases can be monitored and used to optimise the critical step of flocculation and design the thickeners. Its initial speed known as the initial settling rate (ISR) of flocculated suspensions has been used in the optimisation, yet the experimental determination of the speed is currently unreliable. Here, we have proposed and developed a novel method that can automatically detect the mudline formation and determine ISR accurately. Specifically, the settling of flocculated suspensions is filmed using a normal digital camera. The movie is digitised and analysed image by image using an in-house MATLAB code to detect the mudline and its relative position versus time. The relative position as a mathematical function of time is then approximately described by an exponential dependence and regression analysis. ISR is determined by the first derivative of the function with respect to time calculated at the mudline formation. This newly developed technique was experimentally applied to establish the optimal conditions of flocculating fine clay suspensions and clay-rich fine coal tailings from a coal washing plant. Our novel technique is fully automated and provides accurate data needed for optimising the thickening process that are free from potential errors caused by the experimentalist in laboratories.