Research On Ion Adsorption Properties Of Hydrotalcite With Different Morphologies And Its Calcined Products

Aiming at the layered double hydroxide LDH(Layered Double Hydroxides)in this paper,different morphologies of magnesium aluminum aluminum nitrate system LDH were synthesized,and their corresponding roasted products LDO were prepared by high temperature calcination.The chemical composition and crystal structure of LDH and LDO were tested and analyzed,and the target product of the synthesized substance was verified.Three different preparation methods can obtain the crystal phase integrity and crystallized LDH/LDO.By adding ethylene glycol,a magnesiumaluminum hydrotalcite having a rod-like structure can be synthesized by a crystallization method;adding ethanol can synthesize a magnesium-aluminum hydrotalcite having a flake hexagon;and adding tetrapropylammonium hydroxide as a template agent.Magnesium-aluminum hydrotalcite with a cubic structure.Among them,the LDH / LDO sheet has the largest specific surface area and is the most potential sulfate ion adsorbent.Compared with the corresponding LDH sample,the morphology of the LDO obtained by firing is not obvious,and still retains the original structure.The three LDO calcined materials still have a certain layered structure.During the roasting process,the ordered layered structure was destroyed,and its specific surface area,pore volume,and pore size were significantly increased compared to the original sample,and the adsorption potential was significantly improved.Different element ratios of magnesium-aluminum hydrotalcite have different adsorption properties on sulfate ions,and three different particle morphologies have different adsorption properties on sulfate ions.LDH-2 with a sheet structure has the best adsorption.performance.The adsorption effect of LDH on sulfate is greatly influenced by the p H value of the environment.When the p H value increases,the sulfate adsorption rate decreases.This study shows that low p H value is beneficial to the adsorption of SO42-.As the initial concentration increases,the unit adsorption amount of LDH also increases,but the rate of increase of the unit adsorption amount is decreasing.The isothermal adsorption line of LDH has the highest correlation with the L-F equation.From the fitting parameters of the hydrotalcite adsorption kinetic equation at different initial concentrations,it can be known that the process of LDH adsorption of sulfate ions is more in line with the quasi-second-order kinetic model.It can be seen that LDO1,LDO2,and LDO3 all have a certain adsorption capacity for sulfate ions,and their adsorption capacities are stronger than their homogeneous LDH.The adsorption process reached equilibrium in about 30 min,and the adsorption effect of the sheet-shaped LDO2 was still the best of the three.The LDOs obtained by the three preparation methods were all prepared under the ratio of Q2(Mg: Al = 2: 1).The adsorption effect of LDO on sulfate is greatly affected by the environmental p H.As the p H value gradually increases,the sulfate adsorption rate decreases.This result indicates that low p H is favorable for the adsorption of SO42-.The presence of chloride and carbonate ions significantly reduced the adsorption effect of LDO on sulfate ions.The effect of anions on sulfate adsorption follows the order of carbonate ion> chloride ion.In general,the affinity of anions with LDH is related to the ionic radius and anion charge.Compared with carbonate ions,the high affinity of chloride ions for LDO results in a greater effect on sulfate adsorption.The flake LDO has a high sulfate ion adsorption rate and a low adsorption adsorption rate,and has a better adsorbent potential.The adsorption process for all three anions is spontaneous.Adsorption of phosphate and sulfate anions at higher temperatures is more energy efficient than carbonate.It has exothermic properties for carbonate adsorption.The adsorption of sulfate and chloride ions is endothermic in nature.As the initial concentration increases,the unit adsorption amount of LDO also increases,but the rate of increase of the unit adsorption amount is decreasing.The isothermal adsorption line of LDH has the highest correlation with the Langmuir equation.Quasi-second-order kinetic model.The composite cement made from LDO and PO cement at a ratio of 0.15 has the best adsorption effect on sulfate ions.For LDH,surface adsorption is the main binding mechanism.For LDO,the surface adsorption of sulfur-containing compounds is weak,and lattice substitution of sulfur-containing compounds also occurs.The carbonate in LDO will occupy the interlayer hydroxyl positions where sulfate ions can be exchanged and reduce surface adsorption.In the LDO phase,carbonates can participate in ion exchange,but it will also cause partial decomposition of carbonates.