CellGuard^® OP Magnesium Hydroxide Slurry with Deinked Pulp

CellGuard^® OP Magnesium Hydroxide Slurry with Deinked Pulp

In 2018, The United States Environmental Protection Agency recorded 46 million tons of paper and paperboard recycled. The reuse of paper reduces:

• Water Consumption
• Carbon Emissions
• Air Pollution
• Deforestation
• Electricity Consumption
• Oil Consumption
• Heat Energy Consumption

It is all-around better for the planet than the manufacturing of new paper. Deinking is an important step in the process of reusing paper. Deinking is a process used to take the printing ink off paper fibers so that it may be reused.

Traditionally, sodium hydroxide (NaOH) has been the main alkali source used in deinking. But with environmental concerns about the highly saline effluent and the safety concerns of handling a solution with such a high pH, paper mills have been making the switch to Magnesium Hydroxide (Mg(OH)2).

Too much alkalinity can be detrimental. In their article “Substitution of Sodium Hydroxide with Magnesium Hydroxide as an Alkali Source in the Peroxide Bleaching of Softwood TMP”, Hu, H. and Zhang, H. wrote sodium hydroxide has “a drawback of high pH in the initial phase of bleaching, leading to the dissolution of organic substances from the pulp that will decrease the pulp yield and increase the effluent load and, in the end, impact the environment”. Too much alkalinity in peroxide bleaching is not advantageous for paper mills because if it reduces the pulp yield, that affects the mill’s costs on top of the disadvantages the effluent poses on the environment. With CellGuard®OP magnesium hydroxide slurry possessing a pH buffering effect, this can help mitigate some of those issues.

Ink in contact with the paper fiber surface directly is believed to be held on by hydrogen bonding and the rest of the ink is believed to be held on by weak van der Waals forces. Alkaline chemicals will be needed to detach these bonds. One such chemical is the use of an alkali, CellGuard®OP magnesium hydroxide slurry. During the “fiber swelling” stage, an alkali is presented to swell the fibers and soften the ink through saponification. The swelling of the fibers flakes off some of the rigid ink particles and they detach from the paper. Surfactants are introduced to help wet fibers, improve alkali penetration, and keep the ink from reattaching to the paper.

Hydrogen peroxide has been a common bleaching chemical for well over 7 decades now. Hydrogen peroxide bleaching is another important step in the deinking process. Many case studies have observed a large increase in residual peroxide levels in the effluent after bleaching. In the peer reviewed article “Mg(OH)2 Based Hydrogen Peroxide Bleaching of Deinked Pulp” by Na Yun and Beihai He, they saw residual peroxide levels go from 3% to as much as 61% when switching the bleaching alkali from NaOH to Mg(OH)2. This residual peroxide indicates fewer side reactions occurring and offers potential savings on bleach chemical if reused. In some processes, it can even be used to further the brightness of the finished paper. The source and purity of Mg(OH)2 is known to affect peroxide consumption. Synthetically produced CellGuard®OP magnesium hydroxide slurry has >98.6% purity with relatively low transition metals, which can deactivate peroxide.

In that same paper by Na Yun and Beihai He, they cite a Canadian paper mill that saw 25% to 40% reduction in effluent treatment costs after making a complete switch to Mg(OH)2. These savings were attributed to the lower dissolved lignin, acetic acid, and other organic substances in the bleaching filtrate because of Mg(OH)2’s lower solubility and alkalinity.

Another peer reviewed deinking paper titled “Flotation Deinking with Magnesium Oxide as the Alkali Source” by Karen Stack, Alison Featherstone, Simon Baptist, and Matthew Kirk, cites the Norske Skog paper mill at Albury, New South Wales, Australia as having an effluent with an elevated sodium absorption ratio from a high dissolved salt content in the effluent. This was due to the mill using sodium hydroxide for their alkali. The paper mill used its effluent for irrigation on a pine plantain but it was found, due to their high sodium absorption ratio, that it caused the soil pores to clog and denied the trees any nutrients. This is because a high sodium absorption ratio is toxic to plants. The paper mentions substituting sodium hydroxide with magnesium oxide for a better reduction in sodium absorption ratio but it even goes on to say magnesium oxide as a hydrated slurry has shown even better results. Martin Marietta’s CellGuard® product ships as an aqueous slurry and therefore, is ready for deployment, potential savings and benefits for our customers and the environment.

It is also worth mentioning that a complete substitution to CellGuard®OP magnesium hydroxide slurry may save additional chemical costs beyond just alkali and peroxide. If the mill is known to use sodium silicate in their process, our product can reduce its consumption as well, further increasing potential savings.

In the processing of recycled paper, CellGuard®OP magnesium hydroxide slurry is an alternative alkali to sodium hydroxide. It can reduce upfront costs, environmental impact, and overall chemical consumption. Not to mention, it is safer to store and handle than traditional bleach chemicals. In conclusion, CellGuard®OP magnesium hydroxide slurry is an efficient alternative alkali in the world of recycled paper. Our product comes from sources that provides the utmost purity, making our product the alkali of choice.