General Chemical provides a breadth of products for the pulp and paper industry. We have strong credentials in drainage and retention, sizing, pulping, bleaching, dechlorination, deinking, pH adjustment, tall oil splitting, brightness enhancement, neutral and acid papermaking, and process and wastewater treatment. In addition we are North America's largest producer of alum with a plant network built to service the pulp and paper industry.

Application	Product
Process water and wastewater treatment	Alum Hyper+IonTM-Polaluminum Chloride Products Ferric Sulfate
Precipitation of rosin sizing	Alum Gen+IonTM-Polaluminum Hydroxychloride Products
Mordant to set anionic dyes on paper	Alum
Drainage and retention aid	Alum Gen+IonTM-Polaluminum Hydroxychloride Products
Pitch control	Alum Gen+IonTM-Polaluminum Hydroxychloride Products
pH Control	Ferric Sulfate
Generation of chlorine dioxide	Sulfuric acids
Wood pulp processing	Sulfuric acids

The most important use of alum is its ability to impart water resistance ("sizing") to paper. Sized paper becomes resistant to penetration by water or aqueous liquids.

Rosin is the most commonly used sizing agent to impart a moisture-resisting property to paper. The role of alum in paper sizing is to precipitate rosin size on pulp fibers prior to their being formed into a sheet of paper.

Most of alum's applications depend on the strong positive charge its polyvalent species have in solution. The aluminum-rosinate reaction is the key to paper sizing. When used with a soluble soap rosin sizing, alum fulfills three critical functions:

• It provides the acid condition and aluminum ions that precipitate the size.
• It gives the precipitate a positive charge that attracts it to the negatively charged fiber surface.
• During drying, the aluminum anchors the hydrophobic portion of the aluminum-rosinate precipitate. It improves the performance of synthetic sizes by providing cationic charges to the largely anionic pulp furnish and assists size retention accordingly.

Alum also performs an important role as a retention aid for fines (fiber fragments) and fillers. At stock pH near and below 4.5, trivalent aluminum ions are present and act as and electrostatic bonding agent. As the negative charge of the system is reduced, particles are allowed to approach each other more closely. As pH approaches 6.0, cationic floc is formed, which behaves differently from the aluminum ion at the lower pH level. Aluminum hydroxy compounds absorb onto the negatively charged fiber surface to form positively charged patches. Negatively charged fiber fines and mineral fillers are attracted to and held by these patches with emphasis on electrostatic bonding and less on entrapment. With this mechanism, the retention is increased, allowing alum to precipitate and retain dyes, latex and dry strength additives as well as fines, fillers and microparticulates. With this more orderly retention, the sheet is "opened up", resulting in increased water drainage which permits faster machine operating speeds.

Alum can offer several other benefits when used in the paper industry, including:

• Reducing deposits on equipment, particularly when added to highly resinous, unbleached stock to precipitate the resins naturally found in the fiber
• Removing turbidity and color in high-quality water, by acting as a coagulant, particularly in mills producing bleached pulp & paper grades
• Removing suspended solids, reducing BOD and color for effluent treatment in pulp & paper mills, by effectively acting as a flocculant and coagulant
• Setting acid (anionic) dyes on paper as a mordant
• Assisting in setting many wet strength chemicals
• Improving paper machine save-alls operations, where fibers, solids and water are separated and reused
• Adjusting wet end pH
• Controlling foam
• Reducing press picking
• Wet strength resin curing and broke recovery

• Alum used in Alkaline and Neural Sizing Systems
• Getting the Most From Your Alum
• Retention, Drainage, and Pitch Control with Alum

Research and technology are breathing new life into alum, one of the industry's most familiar and well-established process chemicals. After over a century of consistent performance, new uses continue to be found for this versatile material. Here is a review of some of these.

• Some producers of lightweight coated papers have adopted neutral or "pseudo-neutral" systems to incorporate calcium carbonate into coating formulations. They generally use alum at a rate of 3 to 7 lb/ton to coagulate fines and trash in the system without the cost and potential formation problems polymers might bring.
• Woodfree printing and writing papers have seen the biggest swing to alkaline papermaking. In this sector, alum is commonly applied in moderate amounts for trash collection and/or reduction of tackiness in reactive size. It is typically added at a rate of 3 to 5 lb/ton at the suction side of the fan pump.
• Some mills also use alum to help control "white pitch" in the stock prep area. Here again, alum can be an effective coagulant for trash. Some mills using synthetic sizes have reported a reduction in press picking with alum. This is thought to be caused by a reduction in the tackiness of the size hydrolysis products.
• Recycled fiber is often a major raw material in packaging papers. This means that adhesives, high levels of fines, and other contaminants will be in ample supply. Use of alum under either acid or neutral conditions can help bring this problem under control.
• It is also possible to use alum with polyaluminum chloride (PACl) to control recycle-related contaminants. Alum-PACl combinations give cost-effective performance at the proper addition points and addition rates.
• Alum is still considered the best available technology for some papers, especially groundwood grades. Mills producing these papers often use 20 to 25 lb. of alum/ton of furnish along with rosin-based sizes at a pH near 4.5.
• In producing de-inked pulp, alum finds use in clarifying pulp whitewater and in lowering pH to the neutral range after de-inking and washing sequences.

Given the diversity of its current uses, it is clear that papermakers still see alum as an important tool in grade development and as a contributor to process efficiency.

Neutral sizing systems, which operate at a pH of 6.0 to 7.8, combine the benefits of acid and alkaline sizing for fine paper, linerboard, newsprint and other products. Polyaluminum chloride (PACl) has become an essential component in these systems.

When PACl and dispersed rosin size are used together in the neutral pH range, they accommodate the addition of calcium carbonate filler or carbonate-containing secondary fiber. They also alleviate problems often encountered with alkaline papermaking, such as increased slip and poor adherence to dryer surfaces.

As a highly-charged cationic material, PACl is an excellent anionic scavenger. This enables it to provide other benefits in neutral systems. For instance, it improves the retention of size, fines and fillers (see TechTalk, at left) and increases drainage. It also is a prehydrolized compound, so it does not depress wet-end pH nearly as much as when aluminum is added via aluminum sulfate or chloride.

By depositing anionic cellulose degradation products on fibers, PACl ensures that they leave the system on the formed sheet. Since these products can hinder drainage, their removal boosts the speed and completeness of water removal. This is especially important on drainage-limited machines for linerboard and other heavyweight grades, allowing faster speeds and/or improved drying.

As hydrolyzed polynuclear aluminum species, PACl offers a particularly effective way to coagulate pitch particles and deposit them on fiber surfaces. Many mills form hydrolyzed products in situ with caustic soda and alum. Use of PACl allows for greater precision because it can be placed at the exact location where pitch control is needed.

In order to get the most from PACl in neutral sizing, mills should choose an addition point that allows for optimal contact time and degree of mixing so the PACl is rapidly distributed through the system.

• Improves retention
• Increases drainage
• Aids pitch control
• Minimal pH depression
• Accommodates calcium carbonate in the system

Ferric sulfate acts as a sludge conditioner in mill effluent treatment. When used with specialty polymers, ferric sulfate enhances floculation for improved sludge dewatering while it removes hydrogen sulfide in the effluent. Left untreated the hydrogen sulfide can lead to corrosion and odor problems. This dual treatment translates to reduced polymer usage and improved odor control.

• Improves flocculation and sludge dewatering
• Improves odor control
• Reduces corrosivity of effluent
• Reduced polymer usage in many cases