Synthesis Of Two-dimensional Layered Metal Sulfides And Their Adsorption Properties Study For Pb²⁺ And Cu²⁺ In Wastewater

With the progress of economy,science and technology,the problem of environmental pollution has become increasingly prominent.Heavy metals are difficult to decompose and easy to be enriched in living organisms,causing great harm to the physical and mental health of human beings and the survival of animals and plants.Therefore,it is of great significance to develop the technology of efficient treatment of heavy metal wastewater for ecological environment and human health.It is of great significance to develop adsorbents with high efficiency and selectivity to treat heavy metal ions.The efficient enrichment of low concentration of heavy metal ions such as Pb²⁺and Cu²⁺in complex mine wastewater containing large excess of competitive ions is challenging.In this paper,two new layered metal sulfide adsorbents（LMS-I and LMS-II）were prepared to treat mine wastewater containing Pb²⁺and Cu²⁺,aiming to solve the environmental pollution caused by industrial wastewater containing heavy metals and provide experimental basis for the application of layered metal sulfide in the environmental field.The research has important practical significance and application.The specific research work and main achievements of this paper are as follows:（1）A layered metal sulfide(K_1.87Zn_0.13Sn_6.4S_12.67,LMS-Ⅰ)was synthesized by solvothermal method with anhydrous K₂CO₃,Zn powder,Sn powder and elemental sulfur as raw materials.The materials were characterized by SEM,TEM,XRD,TG and BET.The material exhibits fast and efficient adsorption bahavior with high adsorption capacity,the large distribution coefficient value.The effects of adsorbent dosage,p H,adsorption time and temperature on adsorption capacity were systematically investigated.When the dosage of the adsorbent was 5 mg,the p H value was 6,the adsorption time was 4 h,the temperature was25°C,and the initial concentration of Pb²⁺was 150 mg/g,which the maximum adsorption capacity of the LMS-Ⅰadsorbent for Pb²⁺was 452.32 mg/g.It is found that LMS-Ⅰhas excellent adsorption properties for Pb²⁺even at high concentration of Cd²⁺、Co²⁺、Ca²⁺、Al³⁺,and Mn²⁺,which the maximum separation factor was 550.42.By studying the adsorption kinetics,adsorption isotherms and adsorption thermodynamics,it is found that the pseudo-second-order kinetic model and Langmuir adsorption isotherm can be used to describe the adsorption process of Pb²⁺on the LMS-Ⅰadsorbent,which indicates that the adsorption of Pb²⁺on the LMS-Ⅰadsorbent belongs to homogeneous chemisorption.XPS analysis shows that the adsorption of Pb²⁺by LMS-Ⅰis mainly caused by chemical reaction（Pb-S）and ion exchange(Pb²⁺-K⁺).（2）Furthermore,using anhydrous K₂CO₃,Zn powder,Sn powder and elemental sulfur as raw materials,adding P₂O₅ to improve the composition of the material.During the synthesis process,taking the different ratios of P₂O₅ and S as variables,three kinds of layered metal sulfide adsorbents(K_1.1Zn_1.02Sn_3.13P_2.75S_8.65,LMS-Ⅱ)were synthesized with different ratios,and the best one was screened out through experiments to treat the heavy metal wastewater containing Pb²⁺and Cu²⁺.Meanwhile,the problems of low adsorption capacity and poor applicability of the LMS-I adsorbent were improved by the LMS-II adsorbent.The morphology and composition of the synthetic adsorbent were analyzed by SEM,XPS,XRD,BET and TG,and the effects of the addition and dosage of P₂O₅,p H,temperature and initial concentration of metal ions on the adsorption of Pb²⁺and Cu²⁺were systematically investigated.It was found that the introduction of P₂O₅ improved the structure and adsorption performance of the materials.Under the optimum experimental conditions,the adsorption capacity of LMS-Ⅱadsorbent for Pb²⁺and Cu²⁺is 476.5 mg/g and 339 mg/g,respectively.The results of adsorption kinetics show that the pseudo-second-order kinetics fits the adsorption process of Pb²⁺and Cu²⁺and the correlation coefficient can reach 0.999,which indicates that adsorption process is controlled by chemical adsorption.The Langmuir adsorption isotherm model was more consistent with the adsorption process,which indicated that the adsorption of Pb²⁺and Cu²⁺on LMS-Ⅱadsorbent was monolayer adsorption.The adsorption mechanism of Pb²⁺and Cu²⁺was further investigated.On the one hand,S and P in the material have a strong affinity for Pb²⁺and Cu²⁺,so the chemical adsorption is the main one.In addition,K⁺and Zn²⁺contained in the material have a certain ion exchange ability for Pb²⁺and Cu²⁺.