Syntheses of layered double hydroxides (LDHs) were carried out using acid leachates of various iron and steel slag as a raw material. The behaviors of precipitation and dissolution for various metal components in the leachates were investigated, by considering the material balance in the LDH production process from iron and steel slag. Removal tests of Cr(VI), B, As(III) and Se(IV) in dilute aqueous solution were conducted with the resulting LDHs.

Metal components in the slag are mainly Ca, Mg, Al and Si. The slag leachates contain about 25% of Si component which may not exist in the hydroxide layer of resulting LDHs. The slag leachate with low Si concentration suitable for LDH synthesis can be obtained by controlling the acid leaching condition of slag successfully. According to the material balance in the LDH production process, it is found that only the Ca precipitation shows 15% or less and those of other metals such as Mg, Al and Fe are almost 100%. The LDHs synthesized from the slag leachate with low Si concentration have excellent removal ability for toxic anionic species and the ability is almost the same as that prepared from reagent. By considering the material balance of LDH production process, it is clarified that the decrease in Si concentration in the slag leachate contributes to the improvement of removal ability of the obtained LDHs.

Eco-town projects are valued highly inside and outside of Japan as a way to build a local resource circulating society. The most important point of any Eco-town project is the implementation of a real recycling business, and building a reliable Eco-town brand. In various places in and outside of Japan, a lot of plans similar to Eco-town projects have been built, but many plans have not been fully realized. The main reasons for this are that the concept of plan did not fit the local specifications, and concrete methods for implementation of the projects were not sufficiently clear.

The purpose of this research is for the authors to show that the Eco-town project is suitable, and to present a concrete method for creating resource circulation society that can be tailored to each local region. Then, we attempt to systemize technical elements and functions of Eco-towns, especially from the point of view for making environmental industries.