Flocculation of the Syncrude fine tailings Part I. Effect of pH, polymer dosage and Mg2+ and Ca2+ cations

In a new process of fine tailings disposal, after extraction of bitumen fro m Athabasca oil sands, the slurry, which contains clays, sand and a small a mount of bitumen, is flocculated and thickened into a paste, The effects of pH, polymer dosage and presence of divalent cations on the flocculation of the Syncrude tailings have been studied. The tests were carried out using a high molecular weight polyacrylamide flocculant (Percol 727) over a pH ra nge from 3 to 11. The effect of Mg2+ and Ca2+ ions was also tested. These f actors were analyzed by fitting the experimental data to a polynomial model , which plots flocculation response in the form of contour maps. The maps i dentify the conditions for obtaining high initial settling rates (isr) and/ or low solids content (sc) in the supernatant. At low pH, in which clays te nd to coagulate, the domains of a high initial settling rate (isr) and low solids content (sc) coincide. In alkaline pH, in which clays form stable su spensions, the addition of the flocculant leads to the development of bimod al size distributions consisting of flocs and dispersed fine particles. Flo cculation is much more efficient in the presence of divalent cations over t his pH range. (C) 2000 Elsevier Science B.V. All rights reserved.