Water recovery improvement by shearing of gravity-thickened tailings for cemented paste backfill

Abstract

Abstract In mines present in water-scarce areas, the high-water recovery from paste and thickened tailings results in significant cost savings as compared to recovery from conventional tailings. However, it is difficult to dewater tailings with fine particles. In this study, a pilot-scale thickening test was conducted to improve the underflow concentration by rake shearing. The tailing bed was analysed with computed tomography. The porosity and connectivity were determined using a pore network model (PNM) to explain the dewatering enhancement due to shearing. The results show that the underflow concentration increases from 62.3 wt% to 68.6 wt% when the shear rate of the rake is 2 rpm. The porosity decreases from 47.26% to 40.19% due to shearing, representing a decrease by 14.96%. The connectivity of the pores decreases by 8.9% due to shearing. The pore spaces can be divided into ‘balls’, representing the water storage, and ‘stick’ throats, representing the pore connection in the PNM. The numbers of balls and sticks after shearing decrease by 16.59% and 24.01%, respectively. The concept of the ball-to-stick ratio (BSR) was proposed for a pore structure characterisation. The BSR increases by 20.76% after shearing, which indicates that the drainage occurs in the stick spaces rather than the ball spaces. A case study was conducted in Jiashi Copper Mine in the Taklimakan Desert, which is one of China’s most arid areas. The underflow concentration reached 70–72 wt% by improving the picket quantity and height. Based on the thickened tailing system, 14 mio t of water can be saved per year and a water recovery of 57% can be obtained. Therefore, paste and thickened tailing technology can be used for the disposal of tailings in arid areas.