Mini-Encyclopedia of Papermaking Wet-End
Additives and Ingredients, their Composition, Functions, Strategies for Use
POLYALUMINUM SILICASULATE (PASS)
Composition: A liquid concentrate called "PASS" can be formed by treating an alum solution with a silicate compound. If such an addition were to be continued too far, then it would result in formation of insoluble aluminum silicate. But it has been discovered that partial neutralization of alum's acidity with silicate produces a meta-stable solution with many attributes similar to PAC. For instance, addition to a paper machine system has less impact on pH, compared to addition of an equivalent amount of alum. PASS is unique, however, in its hair-trigger readiness to flocculate and come out of solution. Simple dilution with water, depending on the pH, can result in formation of the characteristic "haze," indicating the presence of colloidal particles. Such particles quickly lose most of their "activity," - something related to their colloidal charge and surface area. Though most soluble aluminum products are noted for their ability to neutralize anionic colloidal charges, PASS usually has too high a degree of neutralization by the silicates to be cost-effective for that purpose alone.
Function: Water clarification, developmental applications in retention and drainage.
Strategies for Use: Because PASS is relatively new on the scene and rather different in character from other cationic inorganic products used by the industry, the best strategies for use are not yet well known. Logic would suggest that PASS is an excellent candidate to consider for applications where one has had difficulties achieving sufficiently rapid coagulation of a colloidal mixture. There is a good example of such an application in the field of water treatment; PASS is effective for water clarification at low temperatures. As noted above, it is not recommended to pre-dilute the product before it is added to a process stream; such dilution is likely to make the additive less effective as a flocculant.
Cautions: The product has limited shelf-stability. Manufacturer's recommendations need to be followed regarding the conditions and time of storage.
PLEASE NOTE: Users of the information contained on these pages assume complete responsibility to make sure that their practices are safe and do not infringe upon an existing patent. There has been no attempt here to give full safety instructions or to make note of all relevant patents governing the use of additives. Please send corrections if you find errors or points that need better clarification.
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This page is maintained by Martin Hubbe, Associate Professor of Wood and Paper Science, NC State University, firstname.lastname@example.org .