Thickening mechanism under high compression stress based on double yield stress: Comparison between compression and compression-shear coupling

Abstract

Tailings thickening is the primary link and key technology of cemented paste backfill (CPB) systems. However, the thickened tailings solids concentration is often substandard because the thickening mechanism under high compression stress (up to 30 kPa) is poorly understood, and is therefore investigated based on the rheological properties of tailings. A self-developed high-compression stress experimental device was used to test the double yield stress (compressive and shear yield stresses) and concentration evolution under compression and compression-shear coupling, respectively. Furthermore, the evolution of floc structure and drainage channels was observed in both scenarios. The results indicate that concentration can be approximated by a power function of the double yield stress, and shear yield stress can be approximated by a linear function of the compressive yield stress. It is found that the linear fitting proportionality coefficients under compression are smaller than those under compression-shear coupling and that the proportionality coefficients in the low-compression stress range are smaller than in the high-compression stress range under compression, but the opposite result is obtained under compression-shear coupling. It turns out that the introduction of rake-shearing action (RSA) by compression-shear coupling mainly improves the thickening rate and the thickening effect in the low-compression stress range. Moreover, by introducing the RSA, the concentration growth ratio also confirms that the compression-shear coupling improves the thickening effect in the low-compression stress range, mainly because the shear action improves the floc arrangement, the drainage channels are more developed, and the drainage rate increases. This study reveals the thickening mechanism under high compression stress from the relationship between double yield stress. Also, it obtains the mechanism by which the RSA increases the dewatering rate in low compression stress.