| As a large pipe "reactor",the retention time of tap water in the distribution pipe network can be as long as one to three days.Due to a variety of physical,chemical and biological reactions occuring in the pipe network,it will have a certain impact on water quality.For the iron-based pipe system,with the increasing years,the problem of pipeline corrosion is becoming increasingly serious.These corrosive substances can release iron ions to the water,at the same time,adsorb and accumulate the various pollutant components of water.In this study,thermodynamics and dynamics characteristics of the heavy metal elements such as Mn,Cd and Ni,and the organic components such as phenol,benzoic acid and catechol were evaluated systematically.On this basis,the theory of adsorption on heavy metals and organic components in corrosive pipes was put forward,and the above process was verified by thermodynamic calculation.The main conclusions are as follows:(1)Iron-pipe Corrosion Materials(ICMs)are mainly composed of Fe,Ca and Zn,as well as a small amount of Al,Mn,As,Pb and Cu;Fe is mainly in the form of goethite.Microscopic analysis results show that ICMs are tumorous in the inner wall of the pipeline.Its structure is relatively loose,with a large number of micro-holes on its surface snd inside.These pores are connected to each other and have a large specific surface area(BET,108.7 m2 / g),which provides a favorable environment for the adsorption and accumulation of pollutants.(2)ICMs' adsorping heavy metal elements process can be divided into three stages: rapid adsorption section,slowly increase section and tend to balance section.With the increase of initial concentration,the adsorption rate of heavy metal elements at certain times showed a certain upward trend,but the time of adsorption equilibrium was increasing.It is found that Mn's absorption on ICMs is mainly composed of physical adsorption,and the conformity of Langmiur and Freundlich adsorption isotherm is higher.Cd and Ni are chemically adsorption and accord with Langmiur adsorption isotherm.(3)With the increase of reaction time,the reaction rate of phenol,benzoic acid and catechol showed similar changes with heavy metal elements,And the adsorption was mainly chemical and belonged to second-order reaction.After equilibration,the removal rate of catechol was the highest,followed by phenol and benzoic acid,which may be related to the charge properties of ICMs surface in the different pH conditions,and the complexing ability of organic components and so on.(4)Based on the data of the main material composition,specific surface area,main active site type and density of ICMs,the adsorption pathways of representative heavy metals and organic components on the surface of ICMs,and the equilibrium constant were determined by Pest parameter rate and Visual Minteq calculation.Through the experiment value and theoretical calculation in the same environmental conditions march comparative analysis,it also can be verified by the model.The above conclusions confirmed that ICMs have good adsorption and accumulation properties for heavy metals and small molecules in organic water.Due to the migration of pollutants to ICMs,the content of pollutants in the pipe network show a certain downward trend.However,when the water quality of the pipe network has changed dramatically,such as switching water supply,it may cause sudden release of pipe attachments,threaten drinking water health.The adsorption mechanism and equilibrium constant of this study will provide theoretical support for the evaluation of adsorption stability of ICMs,the operation and management of pipeline network and the regulation of water quality control. |
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