Preparation Of Modified Kaolin And Its Adsorption Of Copper In Aqueous Solution

Methods of treating heavy metal wastewater mainly include chemical precipitation,ion exchange,electrochemical method,adsorption and membrane separation technology,etc.Among them,the adsorption method has attracted more and more attention due to its advantages such as simple operation,low energy consumption,and low investment.Beside,to develop a cheap and efficient adsorbent is an important direction to deal with heavy metals,especially for the complex heavy metal wastewater.As a cheap adsorbent,kaolin reserves in China are very rich,which has a lower adsorption properties than the orther adsorbents such as activated carbon due to its own physical and chemical structural.Especially for complexation of heavy metals,the adsorption properties of kaolin is not obvious.Numerous studies have shown that mercapto functional groups have a strong chelating effect,which can form stable complexes with heavy metals in water by covalent bonding.However,there are few reports on mercaptan functional groups modified with heavy metals Reported.In this study,kaolin modified by MPTMS(modified kaolin)was prepared through single factor and orthogonal experiments.The FTIR,XRD,BET,Zeta potential,SEM analysis and other characterization methods were used to study the structural characteristics and modifier loading mechanism.The effects of initial concentration,pH value,adsorbent dosage,adsorption temperature and adsorption time on adsorption performance were studied as well as adsorption kinetics model and isothermal adsorption model under optimal adsorption conditions.And preliminary analysis of the adsorption mechanism of modified kaolin.In summary,we have achieved the following results:1.After single-factor and orthogonal experiments,it was found that the optimal conditions for preparing 5g of modified kaolin were:the dosage was 3.0 times the CEC,the modification temperature was 60? and the modification time was 18 hours.The degree of influence of each factor is:dosage of modifying agent>modification temperature>modification time.2.The modified kaolin was characterized by FTIR,XRD,BET,SEM and Zeta potential analysis.It was found that more Si-O-Si and Si-OH were formed in the modification process and the interlayer spacing did not change substantially,which indicating that MPTMS was mainly loaded on the surface of kaolin,and there was less interlayer penetration.The loading method is mainly based on the condensation of silicon hydroxy groups.After modification,the number of micropores and mesopores(<7nm)of kaolin is significantly reduced,the pore diameter is slightly increased,the pore volume is slightly decreased and the specific surface area is significantly decreased as a result of the load of MPTMS,which blocks the pores of kaolin.The surface roughness decreases and the particles on surface become larger and the shape becomes less regular,which reduces the physical adsorption effect to a certain extent after the modification,as a result,the removal of heavy metals after modification is more dependent on chemical adsorption;The surface of kaolin is negatively charged when pH>2.5,the surface electronegativity increases after modification.3.Single factor test was used to study the factors affecting the adsorption of ionic copper(Cu2+)by kaolin before and after modification.The effects of initial concentration.initial pH value.adsorbent dosage,adsorption temperature and adsorption time on the adsorption rate were investigated.The optimum conditions for the removal of Cu2+ by modified kaolin are as follows:initial concentration is 5mg/L,initial pH is 5.5,adsorbent dosage is 0.2g and adsorption temperature is 30?.Under this condition,the adsorption reached equilibrium in approximately 30 minutes,and the adsorption rate increased from 70.0%to 99.3%.4.Single factor tests were used to study the factors affecting the adsorption of complexed copper(CA-Cu)in kaolin before and after modification.The effects of initial concentration,initial pH value,adsorbent dosage and adsorption time on the adsorption rate were investigated.The optimum conditions for the removal of CA-Cu from modified kaolin were as follows:initial concentration was 5 mg/L,initial pH was 5,and adsorbent dosage was 0.3 g.Under this condition,the adsorption reached equilibrium in approximately 30 minutes,and the adsorption rate increased from 36.1%to 93.9%.5.The process of adsorption of ionized copper(Cu2+)and complexed copper(CA-Cu)by modified kaolin is consistent with the pseudo-second-order kinetic model and the Langmuir isotherm model.The maximum adsorption capacity was increased from 0.58 mg/g to 1.45 mg/g and from 0.19 mg/g to 0.54 mg/g,which were increased by 150%and 184%,respectively,indicating that the adsorption ability of kaolin was significantly enhanced after modification.6.The adsorption process of modified kaolin to Cu2+ is the result of the combined effect of physical adsorption and chemical adsorption,including charge adsorption,coordination of surface silanol(Si-OH)and thiol(-SH)and.As for CA-Cu,the adsorption mechanism of modified kaolin is mainly based on the coordination adsorption of mercaptan(-SH),ie chemical adsorption.