Adsorption Of Acid Dye From Aqueous Solution By Calcined Magnesium-aluminum Layered Double Hydroxides

Magnesium-aluminum hydrotalcite-like compounds(LDHs)were synthesized by coprecipitation.The hydrotalcite-like compounds(LDO)was obtained by calcination under 450? and then the LDO has been used as an adsorbent to remove Acid Orange 3(A03),Acid Red 88(AR88)and Acid Yellow 49(AY49).The effects of various parameters on the removal of acid dye such as equilibrium time,pH of solution,concentration of acid dye,and temperature were studied in detail.In addition,the adsorption isotherms,kinetic models(First-order,Pseudo-second-order and Elovich),adsorption mechanism,competitive anions on adsorption and the regeneration of Mg/Al-LDO have also been investigated.The results show that:1.The solid LDO,both fresh and after removal of AO3,were characterized by XRD and infrared spectroscopy.The results of adsorption experiments indicate that the maximum capacity of A03 at equilibrium(Qe)and percentage of adsorption(?%)with a fixed adsorbent dose of 0.2g·L-1 are found to be 1471.0 mg·g-1 and 97.96%,respectively,when A03 concentration,temperature,pH value are 300 mg·L-1,313 K and 7,respectively.the adsorption of A03 is consistent with Langmuir equations,and thermodynamic parameters such as AG0,?H0,?S0 were calculated from Langmuir constants.The negative values confirm the spontaneous exothermic nature of adsorption.The adsorption process followed pseudo-second order kinetic model.The value of Ea was calculated to be 82.63 kJ·mol-1.2.The results of adsorption experiments indicate that LDO could be used to remove anionic dyes of high concentrations and when AR88 concentration,temperature,pH were 2000 mg·L-1,288 K and 10?11,respectively,the maximum absorption volume of AR88 at equilibrium(Qe)and percentage of removal(?%)with a fixed adsorbent dose of 1.0 g·L-1 were found to be 1999.0 mg·g-1 and 99.95%,respectively.The results indicate that the equilibrium isotherms of uptake of AR88 by LDO were well fitted to the Langmuir equation.The negative thermodynamic parameters such as ?G0,?H0 and?S0 calculated from Langmuir constants indicate that the adsorption process is a spontaneous and exothermic process with decreased entropy.Three kinetics models were used to fit the kinetics experimental data,and the pseudo-second order kinetics model could be used to describe the uptake process appropriately.The value of Ea was calculated to be 54.53 kJ·mol-1.The size and arrangement of AR88 molecular on LDHs was simulated using the CASTEP and Focite program,it can be speculated that the major adsorption of AR88 is on LDHs surface with the minor AR88 intercalated into the layer.The regeneration for re-use of LDO after AR88 sorption was feasible with four cycles,which can even reach above 90%.3.The results indicate that when dosage of AY49,initial pH value,temperature are 0.02 g,10 and 288 K,respectively.Adsorption volume in equilibrium and percentage of removal are 738.16 mg·L-1 and 98.42%.the adsorption of AY49 is consistent with Langmuir equations,the adsorption process followed pseudo-second order kinetic model,the value of Ea is 72.51kJ·mol-1,which suggests that the process of adsorption of Acid Yellow 49 is controlled by the rate of reaction rather than diffusion,the possible mechanism for AY49 adsorption has been presumed.