In the last few years, alkali-oxygen bleaching was spot-lighted by its possibility to reduce effluent pollutions and many studies were conducted on it.
It is a fact that possibility of bleaching pulp by alkali-oxygen was known many years ago, but it is only after the discovery by Professor Robert, in France, of the protective action of magnesium compounds against degradation and reduction of viscosity of pulp, that alkali-oxygen bleaching is in realization at industrial scale.
Professor Robert conducted some interesting tests by using cotton linter (Table 1, and 2). From these experiments, conclusions are;
1) More higher is the caustic sada concentration, more higher is the temperature and more longer is the retention time, more lower is the DPm. At contrary, oxygen pressure seems to be of small effect.
2) Presence of magnesium compounds prevent the lowering of DPm. Effect of magnesium compounds acting as a protector is evident.
3) Presence of Fe (and also other heavy metals such as Co, Mn, etc.) precipitates the lowering of DPm.
In alkaline medium above pH=11 the MgCO₃ (same for MgO) will transform to Mg (OH)₂ which is insoluble but in spite of this insolubility magnesium protector removes heavy metals from the solution (Table 3).
Professor Robert says that Mg (OH)₂ probably removes heavy metals by absorption. This absorption theory is a hypothesis now under studies in Grenoble (France) and in 1973 new publications on this subject will be made.
On the basis of the discovery of magnesium protector, L'Air Liquide (France) cooperating with SAPPI (South Africa) started up the first commercial scale alkali-oxygen bleaching unit designed and constructed by Kamyr (Sweden) at Enstra Mill of SAPPI in May. 1970.
The second one with a capacity of 275 t/day started its operation at Grüvön Mill of Billeruds (Sweden) in September, 1972 and is running with success. The third one under construction at Cellulose d'Aquitaine (France) for 480 t/day will start its operation in May or June, 1973 with a capacity of 400 t/day.
For the development of this process, L'Air Liquide built-up near Paris a Pulp and Paper Research Laboratory and is now making tests with samples from all over the world. In the past year, this laboratory made tests with samples produced by major Japanese paper manufacturers. Among them we picked up two typical examples ; The first example, Testing No.210 made with hardwood UKP from Japanese manufacturer A, was bleached by A-O stages in L'Air Liquide Laboratory, this semi-bleached pulp was further bleached in the laboratory of manufacturer A by DED and HDED stages and compared with CEDED and CEHDED bleaching of same UKP. Table 4 to Table 9 show the results of this series of tests.
The second example, Testing No. 112 made with hardwood UKP from Japanese manufacturer B, was completely tested in L'Air Liquide Laboratory. Table 10 to Table 13 show the results of this series of tests.
All the tests at L'Air Liquide Laboratory were conducted by Messrs. P. REROLLE and B. WEINZAEPFEL.

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Some polymers bearing amide groups can be readily converted into the corresponding N-chloroderivatives by treatment with hypochlorite in alkaline medium. The N-chloroamide groups have a high reactivity to the groups having an active hydrogen atom, such as alcohols, phenols, and amines. On this account, various polymer-derivatives bearing N-chloroamide groups were examined as wet-and dry-strength agent for papers. Remarkable increases in dry-and wet-strengths were obtained in low-grade pulp papers, such as news print paper, and in unbleached pulp papers by wet-end addition of the N-chloroamide derivatives of polymers. However, these additives were not so effective for bleached pulp papers. This fact suggests that the N-chloroamide groups can readily react with the unbleached fibers (probably with lignin), forming the closs-linkages between the fibers, and that they, however, can not easily react with the hydroxyl groups of cellulose. The combined use of the N-chloroamide derivatives with a polyamine (aminoethyl cellulose) brought about significant increases in the dry-and wet-strengths of the bleached pulp papers as well as in those of the unbleached pulp papers. This effect may be attributed to the carbamide linkages formed by the reaction of the N-chloroamide groups with the amino groups of the polyamine.

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The main components of polluted water discharged from paper mills are hemicellulose, fiber-fine and polyphenolic compounds, such as lignosulfonate and Kraft lignin.
Beer mills discharge polluted water which contains protein. Thus the mixture of both polluted waters with addition of 1 % Alum produced successfully large amount of precipitant. By contrary, there was no precipitation without addition of Alum. However, the addition of the Alum alone did not contribute to the precipitation of paper mill effluent. This means that the combination with beer effluent is essential.
In addition to this, the presence of clay colloid accelerated the settling time of pollutant. Furthermore, it can be suggested that the precipitant is useful for carrier of control release herbicide and also for filler of paper board.

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