Removing ink from recycled printed papers, known as deinking, has a very short history.
The first North American company to try it out on a large scale was Ontario Paper in their Thorold, Ontario newsprint mill in about 1980. Concern about landfills filling up with old newspapers (ONP) led to California passing legislation in 1989 requiring 50% recycled fiber content in all newsprint consumed in the state by 2000. Several other states passed similar laws, and by the mid-to-late 1990s, deinking plants were being built in multiple locations across the continent with various types of equipment, some of which worked better than others.
One idea I helped a mill try out at that time was a low-capital-cost solution to pulp pressroom waste paper (which was assumed to be low in ink and free of contaminants), using a dispersant to help wash out any ink. This was a low-capital option, but Murphy’s law intervened; there were no cleaners present to remove non-paper debris and we ended up with staples in the paper and machine clothing!
There are two ways to remove ink – washing and flotation. Washing is similar to removing dirt from clothes: add soap and water, rely on the hydrophobicity of one end of the soap molecules to attach to the ink, then drain. In theory, this removes the soap with ink attached, leaving clean fibers behind. While it works well for small ink particles, it doesn’t work very well for larger or well-attached ink particles.
The second way to remove ink is by flotation. A foaming agent is added to a pulp suspension, air is bubbled through the mixture, the hydrophobic ink particles attach to the air bubbles, the bubbles rise and the foam at the top containing the ink is skimmed off – what I like to refer to as a “lift and separate” process. This process uses less water and is more effective for larger ink particle sizes. Most deinking mills today use a combination of flotation and washing in order to remove a wide range of ink particle sizes.
I helped some mills start up and optimize their deink plants in the early years. The time period of approximately ten years to comply with the legislation sounds long, but it took this long to research, pilot, design, finance, build, install and optimize the technology across the continent, not to mention start up collection programs to develop a reliable supply chain for old newsprint fibers.
Another challenge was finding the right things to measure and control in order to improve deinking operations. New methods and instruments had to be developed to measure “dirt” and “stickies.” I worked with one plant that decided, for safety reasons, to put a cover on top of their flotation column without a hatch, and there was no way to see whether the foam skimming operation was working properly. Another plant, in their haste to start up, started operating their flotation column before the building had a roof, and during a thunderstorm, rain beat down the foam at the top of the cell so that the operation had to be stopped until the storm was over.
Today, deinking plant design is fairly mature and standardized. The focus is on optimizing the cost, yield, and quality of deinked pulp. Here are some of the technologies that have been explored and are still evolving:
- Chemicals: New deinking agents and better chemical formulations are being developed to improve ink removal efficiency while minimizing environmental impact.
- Enzymatic Deinking: Enzymes that can help detach inks and adhesives from paper fibers are being used, including cellulases, hemicellulases and ligninases. These help detach ink particles from fibers and can reduce the need for other chemicals.
- Mechanical ink detachment: Kneaders or high-pressure homogenization to detach ink particles more effectively can enhance the separation process during deinking.
- Water Reduction: Technologies that reduce fresh water consumption, such as reverse osmosis and ultrafiltration, can improve energy efficiency by recycling warm water.
- Digital Monitoring and Automation: The integration of IoT and AI to monitor the deinking process helps optimize operational parameters, achieving better quality control and efficiency.
Of course, there are many other issues involved in producing a recycled furnish, such as separation of paper fibers from single-stream recycling, removal of prohibitives (e.g., metal, plastic and glass), disposal of deink sludge, maintenance of equipment subjected to abrasion from contaminants and fluctuating cost of secondary fiber. Managing all these issues along with deinking efficiency provides interesting challenges in the life of a deink plant manager!
Martin Fairbank, Ph.D. Martin Fairbank has worked in the forest products industry for 31 years,
including many years for a pulp and paper producer and two years with
Natural Resources Canada. With a Ph.D. in chemistry and experience in
process improvement, product development, energy management and lean
manufacturing, Martin currently works as an independent consultant,
based in Montreal. He is also an author, having recently published
Resolute Roots, a history of Resolute Forest Products and its
predecessors over the last 200 years.
Martin Fairbank Consulting
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