Influence of shear force on floc properties and residual aluminum in humic acid treatment by nano-Al_(13)

摘要

The impacts of various shear forces on floc sizes and structures in humic acid coagulations by polyalu-minum chloride (PACI) and nano-Al_(13) were comparatively studied in this paper. The dynamic floc size was monitored by use of a laser diffraction particle sizing device. The floc structure was evaluated in terms of fractal dimension, analyzed by small-angle laser light scattering (SALIS). The effect of increased shear rate on residual Al of the coagulation effluents was then analyzed on the basis of different floc characteristics generated under various shear conditions. The results showed that floc size decreased with the increasing shear rate for both Al_(13) and PACI. Besides, floc strength and re-formation ability were also weakened by the enhanced shear force. Al_(13) resulted in small, strong and better recoverable flocs than PACI and moreover, in the shear range of 100-300 revolution per minute (rpm) (G=40.7-178.3 s~(-1)), the characteristics of HA-Al_(13) flocs displayed smaller scale changes than those of HA-PACI flocs. The results of residual Al measurements proved that with shear increased, the residual Al increased continuously but Al_(13) presented less sensitivity to the varying shear forces. PACI contributed higher residual Al than Al_(13) under the same shear condition.