Calcium Oxalate Precipitation in the Presence of Magnesium, Wood Resin and Galactoglucomannans

Calcium oxalate scale deposition is a common problem in pulping and papermaking processes. In this work, we have determined the effects of some dissolved and colloidal substances, which are present especially in mechanical pulping, on calcium oxalate precipitation. Sodium oxalate and calcium chloride solutions were mixed together in the presence of magnesium, colloidal wood resin, and galactoglucomannans in an aqueous test solution. The precipitation kinetics were monitored by an on-line turbidity sensor. The size distribution and hydrophobicity of the resulting particles were analyzed by flow cytometry (FCM), whereas the precipitates were structurally identified by X-ray diffraction (XRD) and visualized by scanning electron microscopy (SEM). The results show that addition of magnesium ions clearly decreased calcium oxalate precipitation and the aggregation tendency of the crystals formed. Colloidal wood resin also inhibited precipitation, but at the same time increased the hydrophobicity of the calcium oxalate particles, suggesting adsorption of resin onto their surfaces. This effect was diminished by addition of dissolved spruce galactoglucomannans, which also remarkably decreased the size of the formed crystals. The findings of this study indicate that dissolved and colloidal substances, i. e., wood resin and galactoglucomannans, play a key role in calcium oxalate precipitation and that their balance in the process should be taken into account when dealing with scale problems. Addition of magnesium salts may also help prevent harmful precipitation in pulping and papermaking.