| As a by-product in waste concrete reuse and disposal,waste concrete powder（WCP）is difficult to utilize rationally due to the large quantity and uneven properties.In order to expand the resource utilization channel of construction waste,based on the summary of domestic and foreign research on the recycling of waste concrete powder,this paper innovatively proposed the thermal modification of waste concrete powder（TMWCP）and applied it to the removal of lead and arsenic in heavy metal polluted wastewater.In this paper,the optimal parameters of modification and the removal characteristics of lead and arsenic of thermal modification waste concrete powder were discussed.The removal mechanisms of lead and arsenic of thermal modification waste concrete powder were explored through microscopic characterization.In this paper,the thermally modified waste concrete powder was successfully prepared,and the effect of preparation conditions on its pollutant removal ability was investigated.The results show that particle size,water-cement ratio and modification temperature all affect the removal ability of lead and arsenic.Either too large or too small particle size is not conducive to the removal of lead and arsenic.In this study,the optimal particle size range of the material was 0.25-0.5mm.The high water-cement ratio can improve the removal ability of lead and arsenic,while the sample with a low water-cement ratio is more sensitive to thermal modification.Due to the change of calcium-binding capacity on the surface of waste concrete powder with different modification temperatures,the optimal modification temperatures for lead and arsenic removal in this study were 850℃and 200℃,respectively.In this paper,the removal characteristics of lead and arsenic by thermally modified waste concrete powder were investigated,and the optimal parameters of each factor were obtained.The study on the removal characteristics of lead and arsenic of the modified materials showed that the materials could effectively remove lead and arsenic in a wide range of initial p H.In this study,the optimal initial p H for removing lead and arsenic of the modified materials were 6.00 and 12.00.Coexisting ion factors showed that Na+,Ca2+,Cl-,NO3-,PO43-and other coexisting ions affected the removal effect of lead and arsenic to a certain extent,and the specific mechanism included the change of surface charge,the competition of adsorption sites and the inhibition of ion exchange.The pseudo-second-order reaction kinetic model can well describe the kinetic process of lead and arsenic removal by the material.The intra-particle diffusion model shows that the binding of contaminants and adsorption sites is the main factor controlling the equilibrium time.Langmuir isotherm equation well simulated the adsorption isotherm data of lead and arsenic removal by modified materials with different temperatures.The maximum removal capacities of lead at 25℃,35℃and 45℃were 46.02mg/g,38.58mg/g and 30.01mg/g.The maximum removal capacity of arsenic was 31.89mg/g,25.56mg/g and 17.42mg/g.The main removal mechanism of lead and arsenic in wastewater by thermal modification waste concrete powder was clarified using microscopic characterization.Through XRD,SEM-EDX,FTIR,XPS,TG and other spectroscopy and non-spectroscopy methods,this study confirmed that the main mechanisms of removing lead and arsenic from wastewater are pore precipitation,ion exchange and surface complexation.BET,Rietveld refining and sequential extraction results indicated that thermal modification changes the pore structure and surface calcium-binding capacity of waste concrete powder,giving the material rehydration ability to enhance its removal ability of lead and arsenic.In conclusion,this study proposed a new idea of resource utilization of waste concrete powder and developed a low cost solid waste-based heavy metal wastewater remediation material.It is of certain significance to broaden the recycling channel of construction waste and solve the‘last kilometer’of construction waste recycling. |
