The role of different alkalis in the deinking process

The effect of deinking using various alkalis has been investigated. Magnesium oxide and ammonium hydroxide showed the same extent of ink removal as sodium hydroxide. The effect of sodium silicate varied with the different alkalis. Silicate free deinking was possible with some alkalis. Variations in the bleaching response of alkalis were observed at the pulping stage. However, due to the complexity of the system, these results were difficult to explain in relation to bleaching chemistry. Significant differences in the strength and optical properties of the pulps also occurred with different alkalis ; these differences can be explained by the hydrolysing effect of the alkalis.