Creating Soil-like Materials For Plant Growth Using Tailings Sand And Fine Tails
Authors: Li X. , Fung M.Y.P. 
Published: March 2010

A major challenge in the reclamation of oil sands processing residues is the re-establishment of self-sustaining ecosystems. The primary task is to develop a technology using these residues to create soil-like materials capable of supporting stable plant and microbial communities. Aggregates (stable agglomerates of mineral particles and organic matter between 0.1 – 10 mm in diameter) can enhance the physical environment of the resulting soil to facilitate the establishment of these communities, and to expedite the process of natural soil structure development.

A procedure was developed to artificially create aggregates using oil sands processing residues, namely tailings sand (TS), mature fine tails (MFT), and composite tails (CT). The clay and water contents played critical roles in the success of the aggregation process. The resulting aggregates had a loam texture, met the size distribution criteria, and were relatively stable. These properties would make them suitable for use as a plant growth medium.

Introduction

Surface mining and water-based extraction of the oil sands in northeastern Alberta have generated large volumes of tailings sand and fine tails. Tailings slurry from the extraction plants contains significant quantities of water, residual bitumen, and coarsegrained and fine-grained materials, all of which are pumped into large settling ponds. The coarse-grained tailings sand quickly settles out to form the dykes and beaches. Much of the fine-grained materials (silts and clays) and residual bitumen precipitate to form an accreting layer which consolidates very slowly. When consolidation reaches 30% solids by weight (one - two years), the resulting deposit is known as "mature fine tails." Currently some 350 million cubic metres of fine tails have been produced and are being stored in large tailings ponds. It is possible that mature fine tails accumulating in the ponds will exceed a billion cubic metres in the ponds by the year 2025.

Recent research to accelerate the consolidation process of mature fine tails has resulted in the development of a treatment method which involves the addition of gypsum (calcium sulphate) to a fine-enriched tailings slurry. The calcium in the gypsum replaces the sodium in the clays of the mature fine tails, resulting in a very rapid release of water (approximately 25% of the volume of the mature fine tails within a few days). The consolidated dense material, now with a solid content of approximately 80% by weight, is termed "composite tails."

One of the major challenges in the reclamation of these residues is the establishment of self-sustaining ecosystems. The primary task is to develop a technology using the oil sands processing residues to artificially create soil-like materials capable of supporting a stable plant community. The desirable characteristics for such materials include:ability to supply sufficient water and nutrients within the root zone for plant growth;providing a physically stable medium for plant growth and be resistant to soil erosion; anda chemically and biologically active medium to buffer the effects of changing environment on plants and soil micro-organisms(1).