?Mining using backfill methods has been utilized by many mines around the world. Tailings thickening, one of the ways to prepare backfill materials, has been studied worldwide and components of the process such as the thickening mechanism of the tailings tank and principles of selecting flocculants have already been worked out. The studies of hindered settling properties of tailings during this process have lagged which can restrict the precise control of tailings thickening and affect the backfill result. Using in-situ tailings from a mine, hindered and polydisperse settling experiments of tailing slurries with different concentrations and different particle size distributions have been launched to study and analyze the hindered settling features of tailing particles. The experimental results show that the R-square figure of the hindered settling rates of classified tailings between calculated values based on Richardson-Zaki model and experimental ones is over 0.87 proving the Richardson-Zaki model can be used to calculate and predict the hindered settling rates of classified tailings. Moreover, Selims theory can capture the main properties of the polydisperse settling process of the mix of sieved and silica tailings. The self-flocculation of fine particles in silica tailings has increased the hindering effect among particles, the experimental settling rates of silica tailings are less than those theoretical values calculated by Selim theory.
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To better understand the inline flocculation technique for enhanced water recovery from fine-particle suspensions, this paper studied the impacts of two typical salts, NaCl and CaCl2 on the geotechnical, hydrological, hydromechanical, and chemical behaviour of polymertreated synthetic tailings slurry using a low-shear mixer for continuous flocculation under controlled conditions. The results are discussed in light of the contribution of the polymer treatment to improved rehabilitation outcomes and the role geotechnical, hydromechanical, hydrological and chemical properties play to achieve this goal.
Improving the dewatering characteristics of high solids tailings streams, by the addition of high molecular weight anionic polyacrylamides is known to be operationally challenging. This is particularly true in applications where a secondary flocculation occurs after primary treatment and thickening of a tailings stream for example, underflow from a thickener or the dredging and re-treatment of unconsolidated material from a tailings dam. Previous experience has shown that high dosages of polymer are often required to increase the initial water release from the tailings on deposition and improve the longer-term consolidation of the deposit. This paper investigates the effect of preconditioning high solids tailings through the use of shear prior to flocculation with the aim of both reducing the overall polymer dose and improving the dewatering performance of the deposit. Data presented includes the effect of preconditioning on slurry rheology and initial water release of the polymer treated material. The work showed that in some circumstances, improvements may be achieved by applying an optimised level of pre-shear, but this is dependent upon the type and properties of the tailings. This study was undertaken on tailings slurries, from different mineral types, that have varying levels of clay and overall solids content.
This paper presents a numerical and experimental investigation of an innovation in thickener feedwell technology. A feedwell plays a leading role in the robust operation of a thickener. Its multifunctional duties include slurry feed momentum dissipation, solids and liquor mass fraction preparation, flocculation, and symmetrical aggregate delivery to the tank. The testing of new concepts in the pursuit of developing a next generation feedwell presented an opportunity to create an improvement in process performance. An alternative method of using a feedwell trough, populated by a multitude of vertically directed nozzles, is adopted. These deliver slurry into a flocculation chamber before dispersing through an exit gap into the thickener tank. The trough most innovatively ensures flash mixing, and highly uniform solids dispersion inside the aggregate growth chamber. Initial examination adopted a multiphase Eulerian mathematical model to explore geometric configurations under various process scenarios. Numerical modelling indicated that when quantitatively compared to an equivalently sized diluting Vane Feedwell TM the design provides a large improvement in solids hold-up, mixing, exit distribution, and more. Modelling advanced to onsite testing of a non-diluting small 2 m diameter prototype in an industrial mineral processing plant. The retrofitted feed system improved thickener performance when compared to the preexisting feedwell and at a newly higher throughput duty. The first occurrence of a networked bed was observed, underflow densities improved by 6.5% w/w, flocculant consumption reduced by 5%, and overflow clarity largely improved. Underpinned by this positive result, modelling has shown even greater benefits may be found in application of the new technology to self-diluting feedwells.