The Distribution of Non-Process Elements in Pulp Mill and Bleach Plant Process Streams. 1. Calculating Precipitation of Inorgani Species

摘要

Non-process elements such as Ca, Fe, Mn, etc. can adsorb on pulp fibers, form complexes with dissolved organic matter, precipitate from solution, or remain in solution as inorganic ions. In designing purge strategies for these elements from pulp mills and bleach plants, it is important 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 solution. The logical first step in developing or evaluating a calculation procedure for the distribution of non-process elements is to address the issue of prediction of precipitation of inorganic salts from solutions of ionic strengths from nearly zero to 4 or more.rnIn 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.