Investigation Of Metal Organic Frameworks For The Adsorptive Removal Of Hydrochloride From Dilute Aqueous Solution

Vast amounts of spent dilute hydrochloric acid are generated with the development of industry.Spent dilute hydrochloride is a major concern due to its highly corrosive and polluting nature.Several methods are suggested for separating hydrochloride from wastewater.These kinds of methods have kinds of disadvantages.While,adsorption is a promising way.Some adsorbents for hydrochloride adsorption have been reported but disadvantages including low adsorption capacity or difficulty in regeneration greatly impede their applications.Metal-organic framework?MOF?,whose porosities are much higher than other adsorbents,can be used as adsorbents to adsorb hydrochloride from wastewater,which can improve the adsorption capacity and reduce energy consumption and the difficulty of operation.In this paper,we used adsorption to adsorb HCl from hydrochloride solutions.Seven water-stable MOFs?MIL-101?Cr?,MIL-100?Cr?,MIL-53?Cr?,MIL-96?Al?,MIL-100?Fe?,UiO-66,ZIF-8?were chosen as adsorbents.The results showed that UiO-66 exhibited excellent stability towards hydrochloride and the highest adsorption capacity among the seven studied MOFs.Further researches on kinetics,thermodynamics,isotherms of adsorption process of hydrochloride on Ui O-66 and its stability towards acid were investigated in detail.From the results,the adsorption rate was rapid,reaching equilibrium in 4 h;the amount of HCl adsorbed on UiO-66increased with the increase of initial concentration of HCl from 0.1 to 0.4 mol L^-1.But that trend slowed down with initial concentration between 0.4 and 1.0 mol L^-1;with the increase of temperature,the equilibrium adsorption capacity of HCl decreased.Herein,different kinds of kinetics models and isotherm models were applied to studied the adsorption kinetics and isotherm of HCl on UiO-66.Results showed that the adsorption kinetics conformed to pseudo-second-order kinetics model and the adsorption isotherm was in accord with Langmuir isotherm.The calculated thermodynamic parameters included?G,?H and?S,which indicated that the adsorption of HCl on UiO-66 was spontaneous and exothermic.Finally,we washed HCl-adsorbed UiO-66 with deionized water and absolute ethyl alcohol for displacing HCl inside the adsorbent.After three recycles,the recovery adsorption rates of HCl on UiO-66 were all above 98.5%,which mean that the ability of regeneration of UiO-66for adsorbing HCl was great.Accordingly,UiO-66 has great prospects in HCl effluent treatment as a cost-effective adsorbent with high adsorption capacity,high recovery ability,and high stability to acidic solutions.Based high adsorption capacity of HCl on UiO-66,we tried to combine HCl extractant with the ligands of UiO-66 to synthesize new types of UiO MOFs.Herein,we synthesized two kinds of organic ligand?BDC-OCH₃,BDC-OCH₂CH₂CH₃?,and used them to synthesized three kinds of Ui Os MOFs?UiO-1,UiO-2?.Used them to adsorb HCl from hydrochloride solutions and compared with UiO-66.The results showed that they had higher adsorption capacity of HCl than UiO-66.And the capacity increased with the increasing of length of side chain of ligand.Accordingly,UiOs MOFs have great prospects in adsorbing HCl from wastewater.