Preparation And Adsorption Behaviors For Inorganic Anion Of Granular Porous Mg/Al Mixed Oxides

Granular porous Mg/Al mixed oxides (GP1-Mg_3.3AlO_4.8and GP2-Mg_3.1AlO_4.6)are preparaed by modified molding method and direct sythesis method, on the basis oflaboratory’s preliminary work. Its adsorption behaviors for inorganic anions (Cr（Ⅵ）,SCN^-and SO₄^2-) from aqueous solution are investigated. Granular porous Mg/Almixed oxides can solve the defects of high dispersibility, poor recycling performanceand easy blocking performance.The structure of GP1-Mg_3.3AlO_4.8and GP2-Mg_3.1AlO_4.6are characterized byanalytical methods of specific surface area and porosimetry system, X-ray powderdiffraction analysis, scanning electron microscopy analysis, fourier transform infraredspectroscopy analysis and thermogravimetry and differential scanning calorimetryanalysis. The results show that the layered structure of Mg/Al-LDH is retained in thepreparation process of modified molding method. The layer charge density decreaseswith an increasing magnesium content, which make the interaction of layers andanions intercalated weakened and layer spacing enlarged. There is not Al₂O₃phase inGP1-Mg_3.3AlO_4.8,however, Al is embedded in MgO lattice. The specific surface areaof GP1-Mg_3.3AlO_4.8and GP2-Mg_3.1AlO_4.6are269.4m²·g^-1and206.3m²·g^-1,respectively. Adsorption behaviors of the former is better than the latter, but the latterneeds less synthetic steps and lower costs.Static adsorption results show that the static adsorption processes of Cr（Ⅵ）,SCN^-and SO₄^2-on GP1-Mg_3.3AlO_4.8and GP2-Mg_3.1AlO_4.6follow Freundlichisotherm equation. The adsorption capacity of Cr（Ⅵ） on GP1-Mg_3.3AlO_4.8andGP2-Mg_3.1AlO_4.6are157.84¹64.95mg·g^-1and82.22¹41.72mg·g^-1from25℃to45℃when the initial concentration of Cr（Ⅵ） is1000mg·L^-1. The adsorptioncapacity of SCN^-on GP1-Mg_3.3AlO_4.8and GP2-Mg_3.1AlO_4.6are165.82¹89.97mg·g^-1and160.64¹84.44mg·g^-1from25℃to45℃when the initial concentrationof SCN^-is500mg·L^-1. The adsorption capacity of SO₄^2-on GP1-Mg_3.3AlO_4.8and GP2-Mg_3.1AlO_4.6are267.18²98.19mg·g^-1and247.73²84.77mg·g^-1from25℃to45℃when the initial concentration of SO₄^2-is1000mg·L^-1. The adsorptionbehaviors of Cr（Ⅵ）, SCN^-and SO₄^2-on GP1-Mg_3.3AlO_4.8and GP2-Mg_3.1AlO_4.6aresignificantly improved than the calcined product of Mg/Al-LDH powder. Theadsorption dynamic processes of Cr（Ⅵ） on GP1-Mg_3.3AlO_4.8, SCN^-onGP2-Mg_3.1AlO_4.6and SO₄^2-on the two adsorbents follow pseudo-first order kineticequation, while the adsorption dynamic processes of Cr（Ⅵ） on GP2-Mg_3.1AlO_4.6andSCN^-on GP1-Mg_3.3AlO_4.8follow pseudo-second order kinetic equation. Theregeneration performance of two adsorbents are so perfect that the removal rate areabove95%for SCN^-and Cr（Ⅵ）,67%for SO₄^2-after adsorption-desorption for fourtimes.Dynamic adsorption results show that some factors such as initial concentration,flow rate, bed height and pH of solution have effects on breakthrough curves. Thestaturated adsorption capcity of Cr（Ⅵ） on GP1-Mg_3.3AlO_4.8and GP2-Mg_3.1AlO_4.6are51.78mg·g^-1and51.30mg·g^-1under the best conditions, respectly. The staturatedadsorption capcity of SCN^-on GP1-Mg_3.3AlO_4.8and GP2-Mg_3.1AlO_4.6are56.32mg·g^-1and51.27mg·g^-1under the best conditions, respectly. The staturated adsorptioncapcity of SO₄^2-on GP1-Mg_3.3AlO_4.8and GP2-Mg_3.1AlO_4.6are193.28mg·g^-1and182.86mg·g^-1under the best conditions, respectly. Yoon-Nelson model can predict thebreakthrough curves of Cr（Ⅵ）, SCN^-and SO₄^2-on GP1-Mg_3.3AlO_4.8andGP2-Mg_3.1AlO_4.6well, while Bohart-Adams model is more suitable for describing theinitial stage of the breakthrough curves （ct/c0<0.5）.The above results show that GP1-Mg_3.3AlO_4.8and GP2-Mg_3.1AlO_4.6which aresynthesized by modified molding method and direct sythesis method, have perfectadsorption behaviors for inorganic anions of Cr（Ⅵ）, SCN^-and SO₄^2-. So they havesignificant industrial value.