Improvement of the mechanical strength of alumina performs by coating with montmorillonite / LDH ge

AcompositematerialwaspreparedfrommontmorilloniteandMg–AlLDH.Theseoppositelychargedparticles form thixotropic gels with distinctflow and micro-structural properties. The stability of the gel was dependent on the montmorillonite/LDH ratio. Novel advanced ceramic materials were designed by coating ceramic preforms with these gels. During calcination these gels decompose to metal oxides, aluminosilicates and spinel. On calcination at 1400 °C, MgO formed from the LDH of the gel reacted with the aluminosilicate formed by the decomposition of the montmorillonite. A non-porous dense matrix was formed with well grown crystals of MgAl2O4 spinel embedded in the aluminosilicate matrix. When the ceramic preforms like porous alumina tube were dip coated with the gel andfired at 1400 °C, the molten aluminosilicate infiltrated into the pores of the aluminum oxide carrying spinel crystals. These spinel crystals settled in the pores and increased the mechanical strength of the alumina tubes. The compressive strength was increased by around 94% and the mechanical extension in the z-direction in the coated body by 4% compared to the uncoated counterpart

Effective Cr(VI) removal from simulated groundwater through the hydrotalcite-derived adsorbent

We investigated the feasibility of using calcined hydrotalcite (CHT) as the adsorbent of chromate to treat Cr(VI)-contaminated water through column tests under varied conditions. The column tests reveal that CHT can take up 34.3-44.7 mg(Cr)/g when the Cr(VI) concentration in the influent varies over a range of 50-200 mg/L (e.g., 0.96-3.85 mM) with pH 6-7 at 298 K. This uptake capacity is only reduced to 29.1 mg(Cr)/g when HCO-3 (1.0 mM) and Cl- (1.0 mM) coexist in the influent. We note that the treated water is of high quality and is free of Cr(VI), with Mg and Al concentrations of <5-10 mg/L, and a pH of 6.5-7.0. The quick desorption of Cr(VI) from the adsorbent (CHT) has enabled us to recover Cr(VI) from the contaminated water and regenerate the adsorbent. All these findings promise CHT as an effective regenerable adsorbent for the remediation of Cr(VI)-contaminated groundwater. © 2010 American Chemical Society.Yunfeng Xu, Jia Zhang, Guangren Qian, Zhong Ren, Zhi Ping Xu, Yueying Wu, Qiang Liu, and Shizhang Qia