Recycled Mail Deinked

flow chart illustrating how ink is removed from paper as it is recycled

I was very curious to understand how my discarded mail pieces were going to be recovered for reuse. So, this is what I learned.

Before your direct mail can be used to manufacture certain grades of paper, the printing inks have to be removed to increase the whiteness and purity. What follow is the process by which these inks are removed from recovered papers. Enjoy!

Recovered Paper: Can be any household mail that you intend to discard such as, magazines, catalogs, and direct mail.

Pulping: The initial pulping is intended to breakdown and detaches the ink from the fibers of the base paper. This process requires the use of some chemicals but the most significant factors are temperature, consistency and efficient mechanical action. The conditions achieved disintegrate the waste paper and aid the detachment of the ink from the paper surface. Considerable attention is given to the timing of the pulping cycle which contributes to the clumping of sticky contaminants and aids their removal at a later stage.

Screen Thickening: To ensure that the ink has been detached and dispersed, a sample sheet is prepared and checked before the stock is diluted and discharged through a coarse dumping screen, to remove large forcing objects, to a holding tank at 5% concentration.

First Stage De-inking: De-inking is carried out using a flotation cell which provides good de-inking efficiency and high fiber yield with minimal water and energy consumption. The process requires the generation of a foam by the injection of air in the presence of a chemical mix containing caustic soda for pH control, a proprietary ‘soap’ as a foaming agent, with sodium silicate and hydrogen peroxide to brighten and clean.

Chemical usage is low and being progressively reduced as further technical developments allow. No chlorine bleaching is used.

Screen Thickening: On leaving the cell, the de-inked stock is further diluted before passing through another fine screening process to remove small solids. The material is then pumped to a drum thickener prior to the dispersion stage.

Dispersion and Secondary De-inking: Thickened stock is progressively dewatered to around 40% concentration in preparation for the kneader disperser stage which breaks down the ink/fiber bonding of more difficult printed materials. Dewatering ahead of kneading is an essential requirement but throughout the entire process emphasis is placed on water recovery and re-use.

The intermediate dispersion stage contributes substantially to the reduction in dirt particles in the finished paper and allows the processing of a wide range of waste papers. The kneading action grinds down contaminants and produces an unavoidable ‘graying’ of the stock, however, the ‘whiteness’ is more than regained through the second stage of flotation de-inking which follows.

Paper machine: Following the de-inking, the stock is pumped to a second drum thickener from which, at around 6% concentration, it is available to be blended with other constituents, if required, ahead of the papermaking process. The deinked fiber is made into a new paper product.

 

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