Statistical modeling of polymer-aided dewatering for tailings thickening

Thickening is the first step in the design of sustainable (cost effective, environmentally friendly, and socially viable) tailings management solutions for surface deposition, mine backfilling, and sub-aqueous discharge. Slurries are converted to materials with superior geotechnical properties by adding polymers. Given the tailings composition, a high settling rate alongside high solids content is achieved by optimizing the various polymers parameters: ionic type, charge density, molecular weight, and dosage. This paper developed a statistical model to understand the dewatering behavior of polyacrylamide-modified tailings by fitting laboratory test data using the method of least squares. A newly devised polymer characteristic coefficient (Cp) that combined the various PAA parameters correlated well with the observed behavior as the R-2 equaled 0.99 for void ratio and 0.98 for hydraulic conductivity. Tailings dewatering widely varied (e = 7.5 to e = 34 and k = 10 cm/sec to k = 10(-4) cm/sec) at low sigma' = 0.001 kPa that corresponded to sedimentation of the feed slurry. The compressibility was found to converge to e = 2.8 +/- 0.2 at sigma' = 100 kPa pertaining to a thickened slurry and to e = 2 +/- 0.1 at sigma' = 1000 corresponding to consolidated tailings. The hydraulic conductivity did not converge and was found to be 10(-5) cm/sec at e = 3 and 10(-6) cm/sec at e = 2. The liquid limit (sigma' = 2 kPa) can be used to differentiate between sedimentation and consolidation. The slurry behaves like a liquid (dominated by the microstructure and seepage through inter-floc voids) for sigma' < 2 kPa and as a solidifying material (affected by pore pressure dissipation through intra-floc voids) at sigma' > 2 kPa. The constitutive equations describing the thickening process were found to be power laws of the form e = a sigma' b and k = 10((c + e d)), respectively, where a, b, c, and d are functions of the polymer parameters.