Tailings pond sludges comprising water, clay, and bitumen mixtures have been treated thermally and with varying levels of electrolytes, acids, oxidizing and reducing agents, and organic flocculating agents to determine optimum conditions for both settling rate and ultimate cake percent solids. Hydrochloric acid and sulphur dioxide were among the most efficient agents and their action could be further enhanced by combining with one of the other methods. Thermal sludge treatment, or treatment with electrolytes or oxidizing agents, less dramatically improved settling rates while carbon monoxide or hydro-treating actually reduced the rate of settling.