Recovery of Fillers from Paper Mill High Ash Sludge by Froth Flotation

The purpose of this project was to recover filler materials (most of which are clay) from the paper mill primary clarifier high and sludge utilizing froth flotation. Initial attempts to determine the dosage of a water soluble cationic surfactant EHDA-Br did not prove successful. It was discarded, an a partially water soluble cationic surfactant was taken up next. With a dosage of 0.75% (based on suspended solids) and an air flow rate of 1.5 - 1.75 1/min. it was possible to increase the ash content over 68% (minimum 66.5%, maximum 69.5%) in the foam fraction after single stage flotation, compared to 51.67% in the original sludge. A maximum filler recovery of 92.8% was also achieved. To achieve these results trails were made over all the pH values from 2 to 12. The ash content (curve) of the sludge was found to be (practically) insensitive to pH variation. When the sludge was treated in a ball mill, with ion exchange resin and sodium hexametaphosphate it was found to be sensitive to pH variation. Only ball milling increased the ash content to 71.6% (filler recovery 91.22%) at pH 3. The treated sludge was of course floated at three pH values 3, 6.5 and 9, and not over all pH values