Removal Of Heavy Metals From Water By Modified Attapulgite

With the development of industrial civilization,the discharge of industrial and domestic sewage is increasing tremendously,which results in the severe deterioration and shortage of water resources.Among kinds of water treatment methods,adsorption method has been widely used in this field.The natural attapulgite,an environmentally friendly adsorption material,is rich in reserves and easy to get,and has the characteristics of a large specific surface area,pore volume,strong ion exchange capacity and complexation.In this study,natural attapulgite was used as raw material,and modified in order to improve its adsorption property for Cd²⁺in water.In addition,the modification mechanism of attapulgite was investigated and the kinetics and thermodynamics of Cd²⁺adsorption were also analyzed.The paper studies four kinds of inorganic modification methods.The effects of adsorption performance of single modification methods of acid and alkali and composite modification methods of acid-alkali and alkali-salt on the attapulgite were investigated respectively.The results showed that the best modification method was alkali modification.The optimum conditions were as follows:the concentration of NaOH,modification time and temperature were 5 mol/L,60 min and 90°C,respectively.The maximum adsorption capacity was 91.03 mg/g.Characterization analysis showed that the modified attapulgite had strong ion exchange,the increasing active site and surface negative charge,in which ion exchange played the leading role.However,the attapulgite modified by acid owned weak ion exchange ability,and the active site and the surface charge were difficult to contact with the heavy metal,which results in the weak adsorption ability.The attapulgite was also modified organically in this paper.The sulfhydryl and amino groups were used to modify acid pretreatmental attapulgite and the response surface methodology and orthogonal experiments were carried out respectively.The result revealed that the modification effect of sulfhydryl modified attapulgite was better,and the optimal adsorption capacity was 30.57 mg/g.The optimum conditions were as follows:the coupling agent dosage,reflux time and pH were 4.90 mL,5.82 h and 6.5,respectively.In addition,the composite attapulgite modified by alkali and sulfhydryl groups showed that the adsorption performance of attapulgite by this method was decreased compared with the single alkali modification.Because the sulfhydryl chains were grafted on the alkali modified attapulgite,the pore volume of attapulgite was reduced and the ion exchange was blocked,which leaded to the decreasing adsorption capacity.Finally,the adsorption kinetics and thermodynamics of modified attapulgite were studied.The results indicated that in the early stage of the adsorption of modified attapulgite was faster,and the adsorption was a spontaneous endothermic process,which was suitable for the reaction in the high temperature environment.At the same time,the desorption of Cd²⁺was carried out in order to realize reutilization.The adsorption amount of modified attapulgite after desorption was 87%of initial modified attapulgite.The desorption efficiency was good,which illustrated that the modified attapulgite was easily to recycle.