Status and prospects of researches on rheology of paste backfill using unclassified-tailings (Part 1): concepts, characteristics and models

The cemented paste backfill (CPB) technology provides a safe, green and efficient access to deep underground mining and sustainable exploitation of mineral resources, and it has become one of the research focuses and development trends in the mining field. The CPB technology mainly includes four key processes, namely, the thickening of unclassified tailings, homogeneous mixing of multi-scale materials, pipeline transportation of fresh CPB, and its consolidation in the mined-out underground stopes. As a relatively new material that is comprised of various constituents, typically the tailings, cement, and water, as well as a high solid concentration, CPB tends to show complicated behaviors under the effects of surroundings. Therefore, understanding CPB behaviors is of practical significance for the development of the technology, since knowledge of CPB behavior is essential in the preliminary backfill system design and operation. It has been pointed out that the use of solid-liquid two-phase flows shows some limitations for the paste. In comparison, the rheology which targets on the flow and deformation of the paste under the influence of external shearing can provide a theoretical basis for the whole processes of paste backfill technology and deeply affect its development. Based on the characteristics of the paste materials, the necessity, particularity and complexity of the research on paste rheology were systematically discussed. Typical rheological properties of paste and the latest achievements were analyzed with the summarized results from rheological experiments. The commonly used rheological models of yielding non-Newtonian fluids were reviewed, and the applicability of corresponding constitutive equations to paste slurry was discussed with reasonable suggestions provided for its practical application. Meanwhile, the key influence factors of paste rheological properties were summarized. According to the research status, the priorities and difficulties of research on paste rheology were summarized and proposed, with emphases on test standards, constitutive equations, microscopic mechanisms and engineering applications.