Deinking of recycled pulps using flotation and magnetic process

42th INTERNATIONAL OCTOBER CONFERENCE on Mining and MetallurgyINFLUENCE OF pH VALUE ON MAGNETIC DEINKING EFFICIENCYMilan . Trumi, Maja S. Trumi Technical faculty in Bor, University of Belgrade, VJ 12, 19210 Bor, Serbia

Abstract

In this paper were presented the laboratory results for magnetic separation (magnetic deinking) of office waste paper (OWP). The efficiency of this process and mass recovery were discussed in relation to pH value. With the rise of pH value (from 8,5 to 10,5) mass recovery in all experiments is increased for 10 % and the efficiency of magnetic separation is increased for 7 %. These preliminary results indicating that the pH value has influence on magnetic deinking process.

Keywords: Office waste paper (OWP), magnetic separationIntroduction

Over the previous decade recycling of waste paper has been improving. But despite the improvements, the amount of paper being land filled has remained constant.

The waste paper consists of cellulose fiber, toner and fillers. Possible methods for recycling paper are: washing, flotation and magnetic deinking. The procedure to be used depends on the type of toner.

Toner is essentially a very small particle of plastic and pigment that is able to maintain a particular polar electric/magnetic charge. The particle may also contain ferromagnetic or other additives in order to strengthen its magnetic properties1.

If toner has magnetic characteristics the best solution for paper recycling is magnetic separation.

Figure 1. A small bead coated with particles of toner1

The magnetic separation process provides an alternative approach to the conventional washing and flotation techniques for deinking of office waste paper (OWP). Magnetic deinking has great potential to improve the efficiency of ink removal due to magnetic content of toners. It is shown experimentally that the magnetic susceptibility of toners typically found in OWP varies from weakly paramagnetic to ferromagnetic. Magnetic deinking of OWP is insufficient to achieve a high quality final product due to variations in the magnetic susceptibility of toner particles. (2,3)Material and the methods of work

Paper desintegration

The waste paper, 22g OWP was used in these experiments. The pulp stream is mixed with 1 % NaOH, 1 % Na2SiO3 and 30 % hydrogen peroxide. All reagents are related to dry paper weight. The pH in this stage is about 8,5-10,5. The control of pH values was done using pH-meter, type MA 5705 Iskra Kranj with combined electrode, type sentix 50. For calibration of pH meter, the buffer solvate was used whose pH value at the temperature of 25 C is 9,18. The reagents are added during the pulping stage, which is carried out at the temperature of 45 C in blender running at the highest speed for 15 minute pulping time at 10 % solids by weight (pulp consistency). The sample prepared that way was left for 24 hours on stand, after adding 100 ml of water so the celulose fibers could swell and easen ink removal.

Figure 2. Paper desintegration

Magnetic deinking

After pulping, the pulp is then transferred to the wet magnetic separator. Density of the pulp is decreased to 1 % of the solid. The temperature of the pulp was 20 C. The 2,2 l of pulp (1 % consistency) were pumped through a glass tube (3 cm inner diameter) and ink was retained on the iron section of a concentric rod (0,8 cm diameter). Subsequently, the magnetic field was released and the ink was washed out with 500 ml of water. This process was repeated twice recycling the water. All experiments were carried out several times.

Figure 3. Davis Magnetic Tube

Analysis methodsHandsheets were prepared from the deinked pulp. The brightness was measured using ELREPHO 2000, which was used for measuring the percentage of reflection of the blue light from the samples at wavelength of 452 nm, according to standard Tappi T 452(4). In order to measure dirtiness of the paper, analysis of samples was done using Image Analyzer V 1,25 2006 MeeSoft, which was used to determine the dirt count.(5) (Dirt count - The average amount of dirt specks in a specific size of paper area. Both virgin sheets and recycled sheets have "dirt," although recycled paper usually has a slightly higher dirt count than virgin paper. However, it rarely affects recycled paper's quality and use).The results of work and discusionThe results of examination are given in the tables. For OWP, the dirt count after disintegration is 6600 ppm and the brightness is 81,60 %.

Table 1. Results of magnetic deinkingpH value of pulpconcentration of solid after desintegration,%Mass recovery

Im, %Brightness after magnetic deinkingB, %Dirt count after magnetic deinking,ppm

Ia8,5180,14 - 82,4084,29 - 86,20 1360 - 1500

Ib10,5190,70 93,2285,80 -87,15 1100 -1270

From the table can be seen that with the rise of pH value (from 8,5 to 10,5), mass recovery in all experiments is increased for 10 % , dirt count is decreased for 245 ppm, and that procured increase of brightness for 1 %.Figure 4. Influence of pH value on brightness Figure 5. Handsheets made from cleaned cellulose fiber (left) and separated toner (right)

Deinking efficiency (E) can be characterized in several ways. The one of them is determining E in terms of the brightness as follows: 100%, (B-brightness after magnetic deinking, Bu-brightness after paper desintegration)6

Deinking efficiency is increased for 7 % with the rise of pH value (from 8,5 to 10,5).Conclusion

The magnetic deinking provides an alternative approach to the conventional washing and flotation techniques for deinking of office waste paper. Magnetic deinking has great potential to improve the efficiency of ink removal due to magnetic content of toners.

These preliminary results indicating that the pH value has influence on magnetic deinking process. Further researches should be directed to optimization of process parameters in order to achieve the maximal mass recovery and quality.References1. http://bss.sfsu.edu/raquelrp/projects/Toner.ppt 2. Azevedo, M. A. D., Miller, J. D., Further consideration of magnetic deinking for wastepaper recycling mills, Recycling Symposium Proceedings, 19983. Ivana Bolanca Mirkovic, Zdenka Bolanca, The optical properties of deinking pulp, The Journal of Imaging Science and Technology, pp. 284-292, 20054. Brightness of pulp, paper and paperboard TAPPI - T 452

5. http://meesoft.logicnet.dk/

6. X.Nie, J.D.Miller and Y.D.Yeboah, The effect of ink types and printing processes on flotation deinking efficiency of wastepaper recycling, Environmental Engineering and Policy, Volume 1, Number 1, Pages 47-58, 1998

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