Enhancement of flocculant-aided filtration performance of coal tailings under alternating low and high shear rates

Abstract

Although flocculation has been widely applied to improve filtration performance before filtered dry stack tailings storage, it is still a challenge to create flocculated aggregates having desired characteristics which are both conducive to improving the filtration rate and reducing the filter cake moisture content. In this paper, the alternate shear conditions were investigated to enhance flocculant-aided filtration performance of coal tailings. The focused beam reflectance measurement (FBRM) was used as an in-situ monitor to measure the floc size under different shear conditions in the presence of anionic polyacrylamide. Compared with single shear conditions, sequenced flocculation produced stronger flocs. It was also found that the flocs formed under two cycles of high (1192.8 s−1) and low (637.6 s−1) shear rates were the strongest and contained fewer particles and small flocs. The particle vision measurement (PVM) was used to analyze the effects of alternate shear conditions on floc morphological characteristics. It was observed that the floc structure became more compact with the number of cycles. Lastly, the filtration experiments were conducted to determine the filtration performance of coal tailings. The results showed that the coal tailings had the best comprehensive filtration performance under the sequenced flocculation with two cycles of high and low shear rates, the filtration time was 12.17 min, which was very close to the fastest 12.03 min of single low shear rate, and 21.2% of cake moisture content was about the same as the minimum 21.1%. The filtration outcomes were consistent with that given by FBRM and PVM.