The accumulation of non-process elements in the recovery cycle is a common problem for the kraft pulp mills trying to reduce their water closure or utilize biofuels in their lime kiln. Non-process elements such as Mg, Mn, Si, Al and P enter the recovery cycle via wood, make-up chemicals, lime rock, biofuels and process water. The main purge point for these elements are green liquor dregs and lime mud. If not purged, these elements can cause operational problems for the mill. This work focusses on the fate of phosphorus in the lime cycle. The main purge point of phosphorus in the recovery cycle is the lime mud. Phosphorus reacts with CaO in the lime during slaking; as a result, part of the lime is unavailable for slaking reactions. The first part of this project, through laboratory work, identified Rhenanite (NaCaPO_4) as the form of phosphorous in the lime cycle and showed the negative effect of phosphorus on availability of lime. The second part of this project involved field studies and performing a mass balance for phosphorus at a Canadian kraft pulp mill.
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