Co-transport Of Nano-biochar And Cd(?)through Saturated Porous Media

In nature,there are a lot of heavy metal pollutants in the soil,atmospheric dust and groundwater environment.Once these pollutants enter the human body with crops,air and livestock waterfowl,they will cause irreversible consequences and not easy to be discharged from the body.In the past most scholars of pollutant migration and tending towards and adsorption colloid carrier migration of pollutants tending towards to do a lot of research,and the adsorption of pollutants for biochar research very much,however,for the biological carbon nanoparticles in geological environment migration study is less,especially when the geological environment of heavy metal pollutants,biochar can promote the adsorption of heavy metal pollutants migration,carry pollutants together know little about the research of migration.In this study,two typical biochar materials were selected and tested by a series of modern analytical methods?infrared spectroscopy,specific surface area,scanning electron microscopy,elemental analysis?to test their surface functional groups,elements contained in them,and related physical properties.By conducting laboratory column experiments,the processes and rules of individual and collaborative migration of nano-biochar?BC?and heavy metal cadmium?Cd?in saturated porous media under different physical and chemical conditions were simulated.Hydrus numerical simulation software was used to simulate the migration process,and a dual-dynamics loci model was established to deeply analyze the influence mechanism of nano-biochar on cadmium migration behavior.The following conclusions are drawn:?1?The biochar characterization results showed that the specific surface area of nano-biochar was 23.90 m²/g and the pore size was 0.045 cm³/g.According to the elemental analysis results,in the process of pyrolysis of wheat straw biochar,oxygen element is lost.In the nano-biochar,the content of carbon?C?element is high,while that of hydrogen?H?and nitrogen?N?element is low.After grinding,the biochar presented powder shape,fine block shape,and occasionally incomplete block shape.The element composition and content were C?70.86%?,O?17.93%?,Ca?0.77%?,K?3.4%?,Mg?0.34%?,P?0.15%?and Al?0.12%?,respectively,with no obvious change compared with the original biochar.Biochar functional groups were similar before and after grinding.?2?The results of the migration test of nano-biochar in the porous medium of saturated quartz sand show that the migration capacity increases with the decrease of the ionic strength IS and the increase of the p H value,while the retention capacity decreases with the decrease of the ionic strength IS and the increase of the p H value.The ionic strength and p H affect the stability of nano-biochar by affecting its surface properties,thus affecting its migration and retention capacity.With the increase of the initial concentration of nano-biochar,the more it was migrated out of the eluent.Under the same physical and chemical conditions,the migration capacity of wheat straw biochar nanomaterials is greater than that of corn straw biochar nanomaterials,which is caused by the different surface functional groups.?3?The experimental study of Cd migration in porous media of saturated quartz sand found that both the ion strength and the p H were important factors affecting the migration of Cd,and the migration capacity of Cd increased with the increase of the ion strength,and increased with the decrease of the p H.As the ion strength increases,K⁺in the system will increase and cationic competition exists for adsorption with Cd to activate the adsorption state of Cd²⁺,which will flow into the pore water and migrate out of the quartz sand column.When p H decreases,H⁺in the system increases,and cationic competitive adsorption exists with Cd,which is conducive to the migration of Cd.?4?On the basis of the study on the independent migration of nano-biochar and Cd,the study on the cooperative migration process and law of nano-biochar and Cd in saturated porous media was carried out.The results showed that the adsorption effect of nano-biochar on Cd was the best when the p H was 6,with the adsorption capacity reaching 36.32 mg/L and the removal rate 92.20%.When the nano-biochar concentration was 600 mg/L,the removal rate?%?of nano-biochar to Cd approached equilibrium,and the adsorption capacity was 32.48 mg/L.The synergistic migration of nano-biochar and Cd has obvious influence on each other.Under different ion strength conditions,nano-biochar can promote the migration of Cd,while Cd can inhibit the migration of nano-biochar.Under different p H conditions,the recovery rate decreased compared with the migration of nano-biochar,and Cd acted as the ion strength to inhibit the migration of nano-biochar.Nano-biochar adsorbs Cd on its surface and stays in the quartz sand column with Cd,which also has an inhibitory effect on Cd migration.When Cd is present in the quartz sand column,the presence of Cd is equivalent to the enhancement of the ionic strength in the solution.The maximum retention of nano-biochar increases from 0.19 mg/g to 0.59 mg/g,and Cd inhibits the migration of nano-biochar.When there is nano-biochar in the quartz sand column,it has a certain adsorption effect on Cd.Most of the two remain in the quartz sand column,thus inhibiting the migration of Cd.