Sodium-Aluminum-Silicate Solids Precipitation from the Build-up of Non-Process Elements in Closed Cycle Kraft Pulp Mills, 1998 Environmental Conference Proceedings

Non-process elements (NPEs) are a major concern for achieving closed cycle operation in Kraft pulp mills. The build-up of NPEs such as Al and Si ions causes sodium-aluminum-silicate (Na-Al-Si) complex formation in the recovery cycle of Kraft pulp mills. These complexes precipitate on process equipment and are very hard to remove.

The purpose of this study is to supply basic data on the precipitation conditions for such complexes. These data can be used directly for the prevention of scale problems in closed cycle mills. In addition, the data can be used to develop process models for design and optimization of closed mills. The precipitation conditions of Na-Al-Si complex were measured in synthetic green and white liquors. The precipitation conditions in mill green and white liquors were also studied. In the experiments the effects of varying the Al/S ratio, OH - , Na2S and CO3 2- concentrations were studied. The structure of the Na-Al-Silicate was identified by X-ray diffraction, thermogravimetry (TG) and chemical analysis. The precipitates were found to have the structure of hydroxysodalite and/or sodalite.