Acid washing and chelation in a displacement system: A comparative study

This paper presents the results of a laboratory study on acid washing and c helation in a displacement system for the removal of transition metal ions from hemlock kraft pulp and oxygen-delignified pulp. It was found that disp lacement chelation with DTPA led to a pulp with a residual Mn content of ab out 30 ppm while a very low residual Mn content (similar to2 ppm) was reach ed for the same pulps by displacement washing with an acidic solution (pH 1 .5). The Inner consists of pumping a pulse of acid solution, followed by de ionized water to displace the acid solution. The key process parameters, su ch as pH, temperature, superficial velocity, pulp consistency, pulp pad hei ght and quantity of acid solution, were investigated to determine their eff ects on the residual transition metal ions of the treated pulps.