Modeling and Simulation of NPE Metal I, 2000 Environmental Conference Proceedings

- Strategies to manage the buildup of nonprocess elements (NPEs) under mill closure will require new process models for pulp washing operations. Toward this end, a steady-state material balance model was developed to predict the partitioning of five metal ions (Na, Ca, Mg, Mn) between the liquor and pulp within the dilution and filtrate recycle stages of a drum washer. Multi-component ion exchange described the competitive adsorption of these metal cations and hydrogen ions into carboxylate functional groups in pulp, and the OLI Systems ESP software integrated equilibrium adsorption and precipitation processes into the material balance model calculations. The effects of wash liquor composition on the distribution of metals within the dilution vat of the washer were simulated. The addition of HCl to the wash stream displaced adsorbed metal ions with hydrogen ions in pH range 2.5 to 5.5, whereas the addition of NaOH promoted the precipitation of Mg+2 and Mn+2 to their hydroxide precipitates at pH 8.5 to 9.5. The addition of Na2CO3 to the wash stream precipitated Ca+2 and Mn+2 to their carbonate precipitates, whereas the addition of Na2SO4 selectively precipitated Ba+2 to barium sulfate.