Equilibria of Cu(II) in alkaline suspensions of cellulose pulp

Interaction of Cu(II) with cellulose pulp was studied by means of polarography, AAS, and ultraviolet–visible spectrophotometry. The experiments were carried out at room temperature and at selected initial cellulose pulp slurry pH values between 7.0 and 13.0. sults obtained showed a trend of decreasing pH after chemical degradation of the pulp (2% w/w) as well as after further addition of a Cu(II) salt (0.5 mmol l−1; pCu=3.3). The pCu in solutions with initial pH values from 7.0 to 11.0 remained in the range 3.4–3.9, implying insignificant complexation of Cu(II). This is almost certainly caused by the relatively low solution pH (5.9–7.4) after pulp treatment and Cu(II) salt addition. When the pH of these solutions was raised to 12.0, the complexing ability of the dissolved cellulose degradation products rises, apparently, due to the deprotonation of hydroxyl groups, and pCu reached 13.0–13.5. he Cu(II) salt was added directly into cellulose pulp slurry at the onset of the alkaline treatment, some of the Cu(II) ions were bound (due to adsorption and/or chemical bonds formation) to the cellulose fibres. The extent of this interaction depended on the initial pH. The bound fraction of the Cu(II) ions represented about 50–70% of the initial Cu(II) amount at pH 7.0 and about 90–95% at pH 13.0. The pCu in filtered solutions with initial pH values in the range 7.0–11.0 remained in the range 3.9–6.1. When the pH of any of the solutions that had initial pH values between 7.0 and 11.0 was increased to 12.0, the complexing ability rised dramatically, and pCu reached 12.9–15.1.