Flotation of soot particles from a sandy soil sludge

In this study the froth flotation technique was applied to clean a sandy so il sludge contaminated with soot particles containing a large amount of pol ynuclear 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 mu m) and silica (90- 200 mu m) 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 degrees to at least 100 degrees and increased the flotat ion recovery from 56% to 100%. However, the contact angle and the flotation recovery of silica are also enhanced under optimal conditions for soot flo tation. A semi-continuous dissolved air flotation apparatus was used for the practi cal flotation experiments. The contaminated sludge fraction contained silic a particles of 20 to 125 mu m and soot particles of 20 to 500 mu m. The bes t flotation results were obtained when a combination of emulsified diesel o il as collector and emulsified Montanol (a mixture of higher alcohols) as f rother was used. Under optimal conditions 95% of the PAHs were removed and concentrated in only 2.5% of the total mass of the sludge. (C) 1999 Elsevie r Science B.V. All rights reserved.