Reduction of the width of particle size distribution to improve pressure filtration properties of slurries

Abstract

The filtration properties of mineral slurries depend for instance on the properties of the solid particles and on the way how these particles arrange themselves when the filter cake is formed. In cake filtration applications, the focus is often on particle size instead of the shape of particle size distribution (PSD). The aim of this experimental study is to demonstrate the influence of the width of PSD on the properties of the filter cake in the pressure filtration of Ni-Cu mine tailings. Modification of PSD is performed by using a stirred media mill at various operational conditions. The results show that not only particle size should be considered when the filtration properties are evaluated: a significant reduction of the average specific cake resistance (>60%) and increase of the average porosity (almost 30%) can be achieved by stirred media grinding at optimal conditions, in spite of reducing the median particle size. On the other hand, the selection of unfavorable grinding conditions may cause substantial increase in cake resistance. Above all, the results imply that the size of particles in the coarse end of PSD should be reduced while avoiding grinding of the finest particles. This seems to be obtainable by paying special attention to the size of the grinding medium. The main outcomes of this study will help in reducing the energy consumption of dewatering of tailings to be disposed of, and recovering valuable elements from tailings deposited in ponds, requiring the use of optimized grinding circuits and solid-liquid separation operations. However, the benefits obtained in the filtration stage should overcome the increased costs caused by the installation and energy consumption of the grinding systems. This means that the demonstrated grinding method may be profitably utilized in industrial scale only when the material is easy to grind and the filtration properties can be significantly improved, or when the filtration plant is the main bottleneck of the process.