製紙スラッジ焼却灰の紙へのリサイクル技術の開発

抄録

Various burning conditions of paper sludge (PS) were examined for the purpose of waste-material recycling. Relationship between burning conditions and reaction products was investigated, and based on the results, optimal condition for recycling PS to use as a filler and a pigment of recycled paper was determined.
The PS ash with high whiteness could be obtained through the general burning process at a high temperature more than 700°C for a long time more than 5 hours. However, this PS ash was not suitable for a paper-filler and a paper-pigment since the pH and electric conductivity values increased too much at the slurry-mixing step due to the formation of gehlenite with high hardness.
Chemical changes of principal components of PS under a heating condition were examined by thermal analysis. Gehlenite was possibly formed from kaolin and calcium carbonate in PS via their thermally-caused change to mata-kaolin and calcium oxide. Since decarboxylation reaction depended on the partial pressure of carbon dioxide (CO₂), transformation of calcium carbonate to calcium oxide could be suppressed by burning PS under CO₂ atmosphere, although transforming reaction of kaolin to meta-kaolin hardly could because of independently from burning atmosphere. That is, decarboxylation temperature of calcium carbonate increased up to 800°C at CO₂ concentration in air of 10% and 900°C at 100%.
Consequently, proper burning condition of PS for recycling as a paper-filler and a paper-pigment was established as follows. Burning temperature is 700 to 750°C. Burning atmosphere is 10% of CO₂ and 90% of air (20% of oxygen (O₂) and 80% of nitrogen (N₂))