Neutral deinking is one of the most significant changes in deinking for many years for mills that use recycled newsprint and magazine paper mix as their raw material, says Bob Horaceck of Kemira.

Neutral deinking eliminates the need for peroxide, caustic, and chelating agent in the pulper. Mills using neutral deinking are also able to either reduce or eliminate sodium silicate in their processes. And all of this saves money, according to Bob Horaceck.
The more a mill uses chemicals for deinking, the greater the savings it will make by switching to a neutral process.
“You can eliminate all pulper chemicals, with the exception of surfactants in a neutral process. This can yield net savings of between USD 2-5 a tonne.
"The relative cost reduction could be as much as 75% in pulper chemicals. This means that a 500 t/day mill can achieve a net cost reduction of between USD 500, 000 and 750,000 a year. Not only that, you can also make additional
savings downstream as well.”
Horaceck describes neutral deinking as the Holy Grail of the world of deinking, as something that everybody has been trying to find, but without success – until now.“
Kemira is the first company to be able to offer truly neutral deinking, at pH 7, thanks to a new patent-pending technology.”

A truly neutral process

There are a number of ‘quasi-neutral’ and ‘low-alkaline’ approaches, using sodium sulfite, for example, already on the market, but these have only been partially successful.
“Using sodium sulfite limits the pH level in the pulper to 8.2-8.3, because you have to have sodium silicate there. That means it’s not truly neutral.”
Mills that use mixed office paper as their raw material have been able to run their processes under neutral conditions for many years, but they employ a completely different treatment for removing ink from their pulp.
“Now producers using a newsprint-magazine mix can also start to enjoy the benefits of neutral conditions as well, thanks to Kemira’s new technology. They will also be able to make larger savings, as they normally use much more chemicals in their alkaline conditions than mills based around mixed office waste. This is mainly because their raw material contains groundwood.”
Producing newsprint and catalog paper from recycled newsprint and magazine paper is the largest single area in the deinking business, and the mills doing this are the largest in the business.

A complex alkaline process

The main reason the deinking process has been alkaline is because of the caustic used.
"Caustic has been used traditionally to help ‘peel’ the ink off the fibers by swelling them, and immediately you put caustic in, the process becomes alkaline. You also need alkaline conditions to get peroxide to work well,” continues Horaceck.
“If you put peroxide in at pH 7, nothing happens. Caustic helps drive the peroxide reaction, by increasing the pH and reacting chemically with the peroxide.”
Peroxide is needed in the alkaline deinking process to bleach back the brightness that is lost in the process because of the high alkalinity.
“You loose some brightness just by wetting paper. When the pulping process is alkaline and because there’s caustic there, you also get what’s called alkaline yellowing. And you need peroxide to prevent this.
“Two other additives are also needed mainly because of the peroxide. You need sodium silicate and a chelating agent to protect it from being degraded by transitometals in the process.”

Neutral is simple

Kemira’s new technology is built around patent-pending soaps and surfactants, which function in neutral conditions and do not need caustic to help things along.
“In most cases, you need just one additive: a new-generation soap or surfactant,” Horaceck says.
“In some cases, however, using some silicate as well can help. So we actually have two approaches with this chemistry: a truly neutral process, running at pH 7, and a low-alkaline one, running at pH 8.2-8.3, which employs silicate but no sodium sulfite. Avoiding the use of sodium sulfite makes things simpler and gives you bigger savings as well. “
Yellowing is no longer an issue in the truly neutral process, as there is no caustic and no high pH.
“The low-alkaline silicate approach can give you a little yellowing, but not very much. And the advantages of silicate make up for any yellowing.”
A neutral process gives useful downstream savings. In the alkaline process, the pH drops from 9.5 in the pulper to 8-8.5 in the final pulp. In the neutral process, system pH drops from pH7 to 6-6.5, which is much closer to the basic pH of the paper machine and hydro bleach.
“When working with hydro bleach, you usually have to add some acid to adjust the pH to its optimal level, 5.5-6. Running a neutral process, we have to add much less acid, and sometimes none at all.”
A neutral process also gives benefits in the water treatment area. Sodium ions in caustic and silicate drives up polymer use in the clarifyer, and eliminating caustic and eliminating or reducing silicate has the reverse effect.
“This can cut polymer costs by as much as 75%, depending on the mill, and this alone can save you USD 1-1.5 a tonne.”

Huge potential

Most of the potential customers in North America have shown interest to the new approach. The first mill trial with the new technology was started in March 2004. Two out of three trials have been repeatedly extended and are still in operation.
“These customers are major, 400-600 t/d facilities. Some customers didn’t want to switch back to alkaline even temporarily, to run down the alkaline material in their reservoir.”
Neutral deinking or sodium sulfite technology is not suitable for every mill, however, says Horaceck.
“Probably about half of potential customers can get all the benefits it offers. We’re able to predict where the neutral process is applicable and why, however, which means we don’t have to run blind trials.”
There are five further trials scheduled over the coming months in North America. The next step will then be to transfer the technology to Europe and the rest of the world.

(Kemira Solutions 2/2005)

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