The effect of preconditioning of tailings prior to inline flocculation and deposition

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.