alum facilitates the removel of suspended from water b
Answers
Explanation:
Woodard & Curran, Inc., in Industrial Waste Treatment Handbook (Second Edition), 2006
Coagulants
Coagulants such as alum, ferric sulfate, and cationic polyelectrolytes all work by suppressing the zeta potential of the colloidal system to a value sufficiently low that the colloidal particles will collide and then coalesce under the influence of slow stirring. Anionic and nonionic polyelectrolytes can greatly aid in the building of much larger flocculated particles that will both settle faster and produce a less turbid effluent. Used in this manner, the anionic and nonionic polyelectrolytes are referred to as “coagulant aids.”
When alum (Al2(SO4)3.18H2O) dissolves in water, some of the aluminum goes into true solution as the trivalent aluminum ion, Al+++. If there are colloidal particles with a negative surface charge, the trivalent aluminum ions, plus other aluminum species such as Al(OH)++ and Al(OH)2+, will be attracted to these negatively charged surfaces and will suppress the net negative surface charge, which is to say they will suppress the zeta potential. Other metal salts that dissolve to yield trivalent ions, such as ferric sulfate, ferric chloride, and aluminum chloride, coagulate colloidal suspensions with effectiveness similar to that of alum.
Salts that dissolve to yield divalent ions, such as calcium chloride or manganous sulfate, also effect reduction of the zeta potential and eventual coagulation, but with an efficiency far less than the difference in ionic charge might indicate. As explained above, the Shultz-Hardy rule states this effect.