Reclamation of Phosphatic Clay Waste Ponds by Capping. Volume 2: Centrifugal Modeling of the Consolidation Behavior of Phosphatic Clay Mixed with Lime or Gypsum

摘要

The research investigated the use of lime and gypsum as additives which might enhance the consolidation of the waste clays. The results reveal that the pH test provides a rapid method for determining the minimum lime content required for strength producing clay-lime reactions. Lime percentages of approximately 12% were required to achieve the pH level for the clays tested. Miniature vane shear tests showed 28-day strength gains of 3 to 5 times that of untreated clay when 12% lime was added while relatively small strength increases occurred for lower lime contents. In the case of gypsum, the pH test was unsuitable for determining the target gypsum content. Gypsum/clay ratios as high as 12:1 produced practically no strength improvement. Centrifugal model tests revealed that addition of lime hindered the consolidation magnitude of the clays. In the case of gypsum addition, the consolidation magnitude was enhanced. Consolidation occurred more quickly, and final effective clay solids contents approached those of untreated clay. The behavior of clay/gypsum mixtures is similar to that for sand/clay mixes.