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The De-inking Process

Before paper is recycled to make white paper, the ink must be removed from the paper through a process called, intuitively enough, the de-inking process. This process involves physiochemical means that gradually clean and recover the fiber that is later taken to a papermachine that creates the final product. In some cases, even the pulp recovered from the process is in turn itself de-inked and sometimes bleached to produce paper such as graphic paper. Other types of paper that are made from de-inked, recycled paper include newsprint, tissue paper, office paper, and writing paper.

Two major processes are exploited in the de-inking process: washing and flotation. First, the recovered paper is deposited into a pulper drum, where it is mixed with water, washed and rinsed. Some of the smaller contraries(contaminants) are screened out at this stage, then the mixture is then made into a slurry. Surfactants are added and air is bubbled through the mixture. The larger ink particles that were not removed in the washing process are removed here and trapped at the top. The foam that results from the entrapment is then quickly removed, as the foam-trapped ink will be reabsorbed into the pulp if not removed in a timely fashion.

When old newsprint(ONP) grade paper is de-inked, a small percentage of used magazines(about 30%) are added to the mix of paper. The reason for this is that the coatings used contain clay which attracts and attaches to the ink more readily, increasing the efficiency of the de-inking process. Technology has greatly affected exactly how paper is de-inked and the quality of the process depends on the equipment and chemicals used.

Challenges abound in the de-inking field, such as the thermochemical effect called the Summer Effect, caused by tremendous heat which accelerate the paper's aging process while it is in transit aboard trucks and trains in the hot summer months. The increase in heat causes the inks in the paper to bind more tightly, making the process of de-inking more difficult. Research has gone into the use of enzymes, various chemical surfactants, and a variety of washing techniques, such as hyperwashing.

After the pulp is de-inked, it is ready to be run through a paper machine to produce the final paper product. Subsequently, after the paper is finally produced and thoroughly inspected both visually, using a magnifying glass, and mechanically, using a brightness meter. The resultant paper's mechanical properties(e.g. wet strength, tear strength) are also assessed to insure that the desired paper quality is achieved.

De-inking mills have been increasing in recent history, and now there are around 420 de-inking mills worldwide.