The Effect Of Model Compounds Of Humic Acid On Structural Regeneration Of Different CLDHs And Their Adsorption Of Borate

Layered double hydroxides(LDHs)are anatural and synthetic anionic clay mineral with layered structure.The calcined products(CLDHs)are widely used in the treatment of various pollutants because of the structural regeneration.Especially as a cheap and efficient borate sorbent,but when they are used in practical applications,the impact of natural humic acid(HA)which are widely exist in nature has to be considered.As an important natural ligand and carrier in environmental media,HA can affect the structural regeneration process of LDHs,and then affect their adsorption of pollutants.However,HA has a complex structure without an exact molecular structure,but has a large number of reactive groups.Using a variety of simple organic compounds to simulate the effect of typical active groups in HA on the structure regeneration of LDHs and their effect on the adsorption of borate is very important for understanding the effect of HA on LDHs,and it is more conducive to the practical application of borate or other pollutants removal by CLDHs.In this paper,typical Mg-CLDH and Ca-CLDH are selected as research objects,and the results of they remove borate alone,interact with different organic models(benzoic acid,phenol,phthalic acid,catechol,2-naphthol,1-naphthoic acid,and 4-phenylbutyric acid),and adsorb borate in the presence of different models are explored.It is found that:(1)When two CLDHs adsorb borate alone,Ca-CLDH has a faster adsorption rate than Mg-CLDH.Mg-CLDH removes borate through electrostatic adsorption and intercalation of borate,while Ca-CLDH removes borate by forming boron-containing ettringite due to the inherent instability of regenerated Ca-LDH.(2)When two CLDHs interacte with the model compounds,it is found that all of them could accelerate the regeneration rate,but only the o-benzene compounds could be significantly adsorbed and affect the regeneration results.O-carboxyl ompounds do not affect the crystallinity of regenerated LDHs.But the effect of o-hydroxyl compounds is related to the type of LDHs: it relatively inhibite regeneration in a short time or at a high concentration,and could damage the crystallinith of Mg-LDH;but it make the crystal growth of Ca-LDH suppressed and inhibite its formation at a high concentration.(3)When two CDLHs adsorbe borate in the presence of models,it is found that they could still strongly adsorb o-benzene compounds.All compounds have a similar promoting effect on the adsorption rate and regeneration rate of Mg-CLDH,and their promoting effect are stronger than HA.In particular,catechol relatively inhibite the regeneration of Mg-LDH.However these compounds degrade the removal of borate by Ca-CLDH,but accelerate the formation of ettringite to some exten.But,catechol severely inhibite the structural transformation of Ca-CLDH into ettringite.The results show that different model compounds have different effects on the structural regeneration of different LDHs,and they also affect their boron removal efficiency and mechanism.And,HA do change the structural regeneration of LDHs and its adsorption of borate through its different active groups.