Flotation of soot particles from a sandy soil sludge

In this study the froth flotation technique was applied to clean a sandy soil sludge contaminated with soot particles containing a large amount of polynuclear aromatic hydrocarbons (PAHs). To obtain insight into the flotation process, contact angles on soot pellets and silica plates were determined in both the absence and presence of several collectors and the results were compared with the flotation recovery of soot (90–200 μm) and silica (90–200 μm) from suspensions of the pure materials using a modified Hallimond tube. Aerophine, dodecylpyridinium chloride and three different oils were used as collectors. Adding a collector increased the contact angles on soot particles from 89° to at least 100° and increased the flotation recovery from 56% to 100%. However, the contact angle and the flotation recovery of silica are also enhanced under optimal conditions for soot flotation. A semi-continuous dissolved air flotation apparatus was used for the practical flotation experiments. The contaminated sludge fraction contained silica particles of 20 to 125 μm and soot particles of 20 to 500 μm. The best flotation results were obtained when a combination of emulsified diesel oil as collector and emulsified Montanol (a mixture of higher alcohols) as frother was used. Under optimal conditions 95% of the PAHs were removed and concentrated in only 2.5% of the total mass of the sludge