Study On Adsorption Behavior Of Pb²⁺ And Cu²⁺ By Thermal Activation Combined With Na₂CO₃ Modified Flotation Tailings

Flotation tailing coal is a high ash product produced in the foam flotation process of coal preparation plant.It has become one of the largest industrial solid wastes in China.A large amount of accumulation will seriously affect regional air,water,soil and other ecological environment,and restrict the sustainable development of coal industry.Therefore,the efficient use of tail coal is of great significance for coal resources and ecological environment.In this study,a series of tailing coal based adsorbents were prepared by nitrogen roasting combined with Na₂CO₃ modification,including unmodified tail coal（TC）,roasting modified tail coal（CTC）,Na₂CO₃ modified tail coal（NTC）,roasting-Na₂CO₃ modified tail coal（CNTC）and Na₂CO₃-roasting modified tail coal（NCTC）.The adsorption effects of various adsorbents on Cu²⁺,Pb²⁺and Cr⁶⁺were investigated.The physical and chemical properties of tail-based adsorbents were characterized by laser particle size,XRD,FTIR,BET,SEM,EDS and C80.The adsorption thermodynamics and kinetics were studied,and the structure-activity relationship between the adsorption mechanism and the structure and adsorption properties of the modified tailing coal was revealed.On this basis,the effects of carbon and clay minerals in the tailings on the adsorption properties of the modified tailings were investigated,and the adsorption properties,reusability and adsorption selectivity of the modified tailings were studied under the optimal modification process.The main results are as follows:（1）Preparation conditions of tailing-coal based adsorbent.When the calcination temperature was 800℃,the calcination time was 1 h,the concentration of Na₂CO₃ solution was1.0 mol/L,and the modification time of Na₂CO₃ solution was 2 h,the prepared CNTC adsorbent had the best removal effect on Cu²⁺and Pb²⁺in water.The removal rates of 50 mg/L Cu²⁺and200 mg/L Pb²⁺were above 98%,but it was not suitable for the removal of Cr⁶⁺.（2）Characterization of tailings coal based adsorbents.The roasting changes kaolinite into metakaolinite and increases the physical adsorption capacity.Na₂CO₃ modification can depolymerize tailing coal to generate amorphous Si O₂ and destroy hydroxyl groups,resulting in more prominent fragmentation phenomenon,larger specific surface area and total pore volume,and the introduction of Na⁺and Pb²⁺ion exchange chemisorption.（3）The role of carbon and clay minerals in tailings coal based adsorbents.Appropriate proportion of carbon content in flotation tailings will promote the improvement of adsorption performance.Compared with the raw kaolinite ore,the space between the kaolinite cells is larger in the tailing coal,which is more conducive to the roasting modification,Na₂CO₃modification and the entry of Cu²⁺and Pb²⁺.（4）Adsorption performance of CNTC.When CNTC dosage was 3 g/L and adsorption time was 240 min at 25℃,the removal rate of 50 mg/L Cu²⁺with initial pH value of 6 reached 98.1%.When CNTC dosage was 4 g/L and adsorption time was 120 min at 25℃,the removal rate of200 mg/L Pb²⁺with initial pH of 6 reached 99.3%.According to the study of adsorption thermodynamics and kinetics,the adsorption process of Cu²⁺and Pb²⁺by CNTC belongs to monolayer adsorption,which is mainly controlled by chemisorption and is a spontaneous endothermic process.（5）Adsorption selectivity of CNTC.In the study of ionic strength and coexisting cations,it was found that CNTC had a good adsorption selectivity for Pb²⁺,but a poor adsorption selectivity for Cu²⁺.In the study of two-component and three-component heavy metal ion coexisting systems,it was found that Pb²⁺and Cr⁶⁺showed inhibition on Cu²⁺,Cr⁶⁺also showed strong inhibition on Pb²⁺,and Cu²⁺could promote Pb²⁺in the appropriate concentration range.