Manufacturing Process of Layered Double Hydroxide Using Iron and Steel Slag as a Raw Material

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.