Removal of metal ions from wood chips during acidic leaching 1: Comparison between Scandinavian softwood, birch and eucalyptus

Acidic leaching of Scandinavian softwood, birch\nand eucalyptus has been studied, for the purpose of removing\nmetal ions from the wood. Equilibrium experiments with wood\npowders were conducted to study the influence of pH. An increased\nrelease of metal ions was found, as expected, when the pH\nwas lowered. For one sample of eucalyptus, the release of calcium\naccelerated when the pH was lowered to below 3, which\nled to the conclusion that a salt of low solubility could be present.\nFurther investigations showed a high concentration of oxalate\nin this sample, which is likely to be an explanation for the\naccelerated release.\nIndustrial cut wood chips, from Scandinavian softwood,\nbirch and eucalyptus, were leached at different temperatures to\nstudy their leaching behavior. Birch and softwood were shown\nto have the same general leaching pattern for calcium and\npotassium. Eucalyptus showed the same leaching trend for\npotassium, but it was harder to remove calcium from eucalyptus\nthan from softwood and birch. In the case of eucalyptus chips,\nwhich had a relatively high content of chloride (480 mg/kg\nwood), extensive removal of chloride was noted.