Fixing of Lead Ions with Calcium-Type Paper Sludge Zeolite

抄録

For the utilization of the paper sludge (PS) ash, we investigated a novel method to remove high concentrated Pb ions from water and fix them. PS ash zeolite (PSZ), which was prepared through an alkali hydrothermal treatment of PS ash with the addition of sodium silicate, was soaked into an aqueous solution of Pb(NO₃)₂ to include Pb ions. The PSZ was heated at a temperature more than 400°C to form PS ceramics (PSC) after being mixed with sodium silicate. The PSC was characterized in terms of morphology, constituent minerals and chemical bonding. In addition, we evaluated the Pb ions fixability of PSC by the determination of Pb concentration eluted from PSC. As a result, detected minerals of PSC's were quartz, albite, nepheline and wollastonite. Each of them appeared or disappeared with changing heating temperature and/or amount of sodium silicate added. Especially in the case of high heating temperature (≥800°C) and large amount of sodium silicate added (≥0.03 molSi/10 gPSZ), nepheline and albite were principal assemblage of PSC and mechanical strength of PSC increased. When nepheline existed in PSC, Pb concentration eluted from PSC was extremely low, showing high ability on fixing of Pb ions. At the same time, the PSC that contained nepheline showed high acidic resistant.
Therefore, it was concluded that the transformation of Pb-included PSZ to PSC that contained nepheline as a principal constituent mineral was much effective for fixing of Pb ions. This novel method will be also applicable to the removal of other heavy metal ions in the water.