Research On Preparation Of Attapulgite Modified Materials And Effects On The Remediation Of Cadmium Contaminated Soil

In recent years,the problem of heavy metal pollution in soil has become more and more important.In the application of heavy metal pollution treatment,attapulgite clay minerals have been practiced a lot,but the selectivity of the natural attapulgite adsorbed heavy metal contaminants and the stability of the products are not strong enough.In view of how to overcome these defects of natural attapulgite,many modifications have been done at home and abroad,and the use of organic modifier is an effective modification method.However,these modified materials have two pollution risk and high price,which is not conducive to the promotion of practical applications.Therefore,to seek efficient and green,inexpensive organic modifier is the key to promote the application of organic modified attapulgite in the treatment of heavy metal pollution.The biochemical fulvic acid contains several binding sites,such as carboxyl group and phenolic hydroxyl group,which can be complex with heavy metal ions,and has the characteristics of green,environmental protection and organic.It is of great scientific significance to study the modification materials of attapulgite and to discuss the properties and mechanism of adsorption of heavy metal cadmium ions,and to develop a new high efficient environment-friendly compound passivation agent for the remediation of heavy metal contaminated soil,which is also beneficial to the rich attapulgite clay mineral and biochemical fulvic acid resource development.The method of surface adsorption modification was selected,using attapulgite as inorganic matrix,the modified attapulgite was prepared by high speed shearing gel method,and its physicochemical properties were characterized by XRD,FTIR,FES EM,TEM and XRF.In order to study the migration and transformation process of heavy metal cadmium ions in the interface of modified materials,the effect of ion concentration,adsorption time,adsorption temperature and pH value on the adsorption performance was studied by using the modified materials with the best quality ratio as adsorbent,and the effects of the ions,the absorption times,the absorption temperatures and the values were investigated.The microscopic adsorption mechanism was studied by XRD,FTIR FESEM-EDS and XPS.In order to study the effect of attapulgite modified material on heavy metal contaminated soil,at the same time,it provides scientific basis for the passivation repair of heavy metal contaminated soil,through the potted experiment of lettuce in the soil contaminated by cadmium,the content of heavy metal cadmium,lettuce growth,effects of soil cadmium bioavailability and soil pH value.The main results were as follows:(1)When the quality ratio of biochemical fulvic acid and attapulgite was 1:10,the adsorption effect of modified material was the best.Through a series of physicochemical characteristics of modified attapulgite,such as XRD,FTIR,SEM,TEM,XRF,the modification of biochemical fulvic acid was successfully confirmed.It was proved that the high speed shearing gel method can graft the organic functional groups in the biochemical fulvic acid into the surface of attapulgite by forming a new covalent bond.(2)The adsorption amount of heavy metal Cd2+ by the biochemical fulvic acid modified attapulgite is significantly higher than that of attapulgite,which could be fitted by Freundlich isotherm.The adsorption Cd2+ process of attapulgite and modified attapulgite was spontaneous endothermic reaction,the adsorption process was rapid,and it accords with the quasi two-level kinetic equation.By the results of XRD,FTIR,FESEM-EDS and XPS showed that the attapulgite is mainly through its surface hydroxyl and Cd2+ coordination reaction,the modified attapulgite is through its surface carboxyl and hydroxyl group and Cd2+ occurrence coordination reaction.(3)The different treatment of attapulgite and modified attapulgite material could significantly reduced the Cd concentration in lettuce.The effect of modified attapulgite on inhibiting lettuce absorption Cd was better than that of attapulgite,which could decreased 41.0%and 56.5%of lettuce on the ground,respectively,and could significantly increased the biomass of lettuce in different treatments.When the dosage was 0.8%,the increase of dry weight of lettuce could reached 30.1%and 33.5%,respectively.Both attapulgite and its modified materials could significantly reduced the Cd concentration of heavy metal in soil,and the amount of 1%could decreased the Cd concentration of CaCl2 extracted state 34.2%and 34.3%,respectively,and the pH value of soil could be increased by 0.19 and 0.07 units,respectively.