Displacement washing with an acidic solution can effectively remove the transition metal ions present in softwood kraft pulps. This paper presents the results of a laboratory study. The process consists of pumping a pulse of acid solution, followed by a pulse of deionized water to displace the acid solution. The key process parameter, such as pH, temperature, superficial veocity, pulp consistency, pulp pad height and quantity of acid solution, were investigated to determine their effects ont he residual transition metal ions of the treated pulps. The results showed that displacemetn acid washing can demineralize the softwood kraft pulp from the initial contents of 142 ppm Mn and 132 ppm Fe to a residual contents of 2 ppm Mn and 15 ppm Fe with about 0.5 bed volume of pH 1.5 acid solution, followed by about 1 bed volume of deionized water to displace the acid pulse.
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