FLOCCULATION OF PARTICLES BY FLUID SHEAR IN BUFFERED SUSPENSIONS

Authors
Citation
Ch. Tsai et Jq. Hu, FLOCCULATION OF PARTICLES BY FLUID SHEAR IN BUFFERED SUSPENSIONS, Water, air and soil pollution, 99(1-4), 1997, pp. 55-62
Citations number
14
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Environmental Sciences","Water Resources
ISSN journal
0049-6979
Volume
99
Issue
1-4
Year of publication
1997
Pages
55 - 62
Database
ISI
SICI code
0049-6979(1997)99:1-4<55:FOPBFS>2.0.ZU;2-M
Abstract
Flocculation experiments were carried out by using a Couette type of v iscometer for applying uniform fluid shears to freshwater suspensions of estuarine fine-grained particles. The suspensions were buffered by a maleic acid/ammonium hydroxide system. The objectives of the study a re to investigate the relationship between the steady-state sizes of f locculated particles and applied shear at various pH values. The resul ts showed that the rate of particle flocculation increased with the ad dition of the buffer. With a particle concentration of 100 mg/l and pH of 6.0, the floc size decreased with the increasing shear. While with a pH of 7.5, the floc size increased with the shear until it reached a maximum value at the shear of 400 s(-1), and then the size decreased as the shear increased further to 500 s(-1). The maximum size shear w as found at 200 s(-1) for pH 7.9. By increasing the pH value to 9.0, t here was no particle growth with any applied shear. The electrophoreti c mobility of the particles was measured. It was found that for any co nstant shear the floc size is inversely proportional to the absolute v alue of the mobility. That is, the more repulsive the force between pa rticles, the smaller the floc size. The effect of pH on floc size was not uniform within the pH range tested. The results demonstrated that the higher the sheat the more significant the changes of floc size due to the pH effect.