Effect of Aluminum Sulfate and Sodium Alumniate on the Drainage and Retention Properties of Fibrous Suspensions

• Main Author: Luu, Wing T.
• Format: Text
• Language: unknown
• Published: DigitalCommons@UMaine 2005
• Subjects: Aluminum sulphate; Suspensions chemistry; Chemical Engineering; Inorganic Chemistry; Materials Chemistry; Carbonic acid
• Online Access: https://digitalcommons.library.umaine.edu/etd/849; https://digitalcommons.library.umaine.edu/context/etd/article/1862/viewcontent/LuuWT2005.pdf

The individual contribution of aluminum sulfate and sodium aluminate for improving drainage and retention properties of fibrous suspensions lias showed limited success as a retention aid. In industrial practice, alum and sodium aluminate additions are often not optimized for retention chemistry, but rather are added to control pH and to precipitate rosin for internal sizing. In this thesis work, the simultaneous addition of these alumin~unc ompounds was invesligated to study its effect on drainage and fine particle retention. Significant improvements in drainage rates and fines retention were observed for simultaneous aluminum addition compared to the individual contribution from each compound. Drainage rates were measured for recycled and mechanical pulps. Drainage rates were characterized by (1) measuring the freeness using the Canadian Standard Freeness (CSF) test and also by (2) determining the viscous drainage resistance coefficient using a dynamic drainage apparatus. For both methods, maximum drainage and retention occurred when a 40160% aluminum sulfate/sodium aluminate ratio was introduced into the pulp. The pH of each system also affected the drainage characteristics and degree of retention. Optimum drainage and retention occurred when the system operated at a pH of 4.5. At this pH level, a soluble alumina +4 polynler, A18(OH)20+4, was formed and had been shown to function as an effective retention and drainage aid. To utilize simultaneous aluminum sulfate (alum) and sodium aluminate as a drainage and retention system, it is recommended that both aluminum compounds are added to a level such that the headbox stock is at or near the isoelectric point. Since the pH of the system will vary with the level and ratio of alum and sodium aluminate added to the system, it is recommended that the pH of the system be controlled separately with the addition of sulfuric acid, hydrochloric acid, carbonic acid, or caustic. The alum-sodium aluminate system is thought to function by having the system at the isoelectric ...