Distribution of Non-Process Elements in Pulp Mill and Bleach Plant Process Streams. 1. Calculating Precipitation of Inorganic Species, 1997 Minimum Effluent Mills Symposium Proceedings

Non-process elements such as Ca, Fe, Mn, etc. can adsorb on pulp fibers, form complexes with dissolved organic matter, precipitate from solu-tion, or remain in solution as inorganic ions. In designing purge strategies for these elements from pulp mills and bleach plants, it is impor-tant to be able to predict what their distribution will be between those adsorbed on fibers, remaining in solution as inorganic ions and ion-organic complexes, and precipitated from solu-tion. The logical first step in developing or evaluating a calculation procedure for the dis-tribution of non-process elements is to address the issue of prediction of precipitation of inor-ganic salts from solutions of ionic strengths from nearly zero to 4 or more. In the study reported here, a chemical equilibrium estimator was used to predict the solubility of several non-process elements in green, and white liquors. Free energy data for the ionic species and precipitate phases and ion activity coefficients were calculated from data bases and an activity coefficient model included with the chemical equilibrium solver. The predicted solubilities were compared with both published solubility data for multicomponent salt systems and data from three kraft pulp mills. The agreement between the measured and predicted was generally good for both green and white liquor streams.