ADSORPTION PROPERTY OF IONIC DYES BY HEAT-TREATED LAYERED DOUBLE HYDROXIDE-CRISTOBALITE ROCK COMPOSITE-MATERIALS

Homogeneous layered double hydroxide-cristobalite rock (LDH-Cb rock) composite materials were prepared by impregnating Mg2+ and Al3+ ions into pores of the Cb rock in suspension state and by successively adding the suspension to Na2CO3 solution at the conditions of pH 10 and 60-degrees-C to hydrolyze these metal ions. The resulting solid products composed of Cb rock and Mg2+-Al3+-CO32- system LDH were heated at 500-degrees-C for 1 h to make an effective composite adsorbent for both acidic and basic dyes. The composite adsorbents, which are composed of Cb rock and magnesium-aluminium oxide solid solution as shown in Fig.5, indicated high adsorpability for Orange II and Methylene Blue. As seen in Figs. 6 and 7, the Freundlich's adsorption isotherm formula can be applied in all cases. The adsorpability per unit weight of the whole composite adsorbent for Orange II was found to be slightly lower than that of the heat-treated LDH, while the adsorpability per unit weight of LDH in the composite adsorbent became 2 to 3 times that of the heat-treated LDH as indicated in Table 1. This should be due to the high dispersion of LDH into the Cb rock. On the other hand, the adsorpability for Methylene Blue based on the negative charge surface of Cb rock in the composite adsorbent was found to decrease by compounding LDH, but the magnitude of the decrease was not much larger than that of the heat-treated heterogeneous LDH-Cbrock composite adsorbent prepared by the another method.