Abstract

Probably the greatest limitation of the Hot Water Extraction Process (H.W.E.P.) is that it results in the unavoidable formation of huge sludge ponds. Despite many attempts, no technology for "dry" tailings production has been commercialized. Several experimental methods of dewatering oilsands sludge have been patented or reported in the literature, but they are uneconomic and/or contribute to serious reclamation problems.

The first step in developing a solution to the sludge disposal problem is to identify the parameters which are significant to the behaviour of clay particles in water and to their separation from it. Several of the most critical properties of oilsands clay sludge particles are identified and discussed.

A knowledge of these properties illustrates why many of the schemes which have been tried have failed or are very expensive. The same properties also point the way to several methods of alleviating the problem by chemically modifying the clay properties and improving the separation efficiency by using the sand to offset the separation problems of the clay fines.

Parallels from solutions developed for other worldwide mining waste slimes and sludge disposal situations are examined for suggestions on how oil sands tailings can be handled.

The basic clay and sand properties and the parallels from other sludge disposal operations have suggested to the author that the best approach for tailings treatment is to treat whole oil sands tailings with lime which is expected to give high water separation efficiency and reasonablv good soil properties.

The progress of the ongoing laboratory research program is presented. and discussed, along with disposal system design implications as we understand them so far.

Introduction

Most people at all familiar with oil sands mining are aware of the magnitude of the tailings disposal problem. However, not everyone realizes that this disposal problem is comparable to other mining operations which produce "slimes" and contain them in large dykes. Oil sands plants are distinctive only because the ponds are larger than elsewhere r because they are often partially c:'overed with bitumen which causes problems for migrating water fowl and because the water is so toxic to fish it cannot be released to nearby water streams. The slimes or sluCl.ge "problem" has been overcome for a number of these operations (1. Martin et al, 1971).

Previous Research on Sludge Disposal Alternatives

Many schemes to improve the settling rate and reduce the compacted volume or water content of oil sands sludge have been proposed and tested since before the first oil sands plant began operating in 1967. An exhaustive review of all the techniques which have been attempted is beyond the scope of this paper. It is probably safe to say that very few stones have been left unturned in an effort to find a technically viable way to reclaim and revegetate sludge; Economically, if possible.

Several schemes have been tested which are capable of inproving the settling and compaction of oil sands sludge (2. Ritter, 1981, 3. Joshi et al, 1982).

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