Effect Of Agricultural Organic Inputs On The Ferrihydrite Nanoparticles Transport And The Prediction Of Synergetic Arsenic Transport

Mastering the mechanism of arsenic(As)adsorption and transportation in the environment is crucial to the control of arsenic pollution.Ferrihydrite(FH)is a common kind of nanoparticles in soil,which can adsorb arsenic in large amounts.At the same time,due to the strong shuttle of nanostructures in the medium,it can carry arsenic for long-distance transportation in the environment.Humic acid(HA)is an important organic matter in the soil.Humic acid will control the arsenic transport by ferrihydrite nanoparticles(FHNPs)through physical and chemical adsorption,thereby affecting the solid-liquid distribution of arsenic in the soil solid phase and pores proportion.Agricultural organic inputs(biochar(BC)and swine manure(SM))applied to the soil will affect the ferrihydrite nanoparticles transport and coordinated arsenic transport by releasing organic matter.Existing studies have clarified the transportation promotion mechanism of humic acid of different forms and concentrations on the ferrihydrite-arsenic complex under different pH conditions,but the process of the competitive adsorption of humic acid and arsenic on the ferrihydrite is not clear,and the mechanism of agricultural organic inputs to simulate the effect of humic acid on the ferrihydrite nanoparticles transport and the coordinated arsenic transport is unclear.In this paper,the adsorption experiment is firstly used to quantify the competitive adsorption of ferrihydrite nanoparticles by humic acid and arsenate(As(?))through Langmuir and Freundlich adsorption isotherm models;then the adsorption mechanism is used to guide the transportation experiment,that is,the dissolved organic matter released by agricultural organic inputs(biochar and swine manure)was used to simulate humic acid.The nanoparticle transport model and extended Derjaguin-LandauVerwey-Overbeek(XDLVO)theory are used to explain the mechanism of its influence on the ferrihydrite nanoparticles transport;finally,the results of comprehensive adsorption and transportation experiments predict the effect of agricultural organic inputs on the ferrihydrite nanoparticles-arsenic complex transport.This paper can lay the foundation for the geochemical cycling of heavy metal arsenic in the soil environment by soil organic matter,soil nanoparticles and agricultural organic inputs,and can also guide the selection of biochar and swine manure inputs and application timing in agriculture.Mainly obtained the knowledge of the following aspects:(1)The adsorption of As(?)by FHNPs is more suitable for the Freundlich adsorption isotherm model.The adsorption of As(?)and HA by FHNPs decreases with the increase of pH(4,7.5,9),respectively.Compared with As(?),FHNPs preferentially adsorb HA.Under the same pH condition,with the increase of HA concentration,the competitive adsorption of FHNPs by HA and As(?)increases,and the negative zeta potential of FHNPs increases;(2)Organic matter effectively regulates the transport of nanoparticles.It is shown that DOM released by agricultural organic inputs(0.2%~10% BC and 0.2%~2% SM)reduces the zeta potential of FHNPs,which further leads to electrostatic repulsion,osmotic repulsion and elastic space repulsion between FHNPs and mixed sand to enhance the transport of FHNPs.Due to the increase of DOM,the transportation of FHNPs increases with the increase of BC and SM content.The surface roughness of agricultural organic inputs(biochar and swine manure)becomes the main factor to inhibit FHNPs transport when DOM is fully released.When the content of BC increased to 10% and the content of SM increased to 2%,the inhibition of surface roughness to FHNPs transport gradually strengthened.The FHNPs retention increased in water treated biochar or water treated swine manure.The retention of FHNPs was strongest in alkali treated biochar(0.2%~10%)or alkali treated swine manure(1%~2%)mixed sand columns,indicating that fully aged agricultural organic inputs would strongly inhibit the transport of FHNPs.The key effect of agricultural organic inputs and its aging on FHNPs transport change from gradual enhancement to inhibition;(3)Prediction: Under acidic pH conditions,the FHNPs-As(?)is deposited in the agricultural organic inputs-ferrihydrite nanoparticles-arsenic system.Under neutral and alkaline conditions,with the increase of agricultural organic input content,the FHNPs-As(?)transport in the system increases firstly and then decreases.At the initial input,the DOM released by biochar and swine manure enhance the FHNPs-As(?)transport.When the DOM is completely released,the surface roughness of agricultural organic inputs plays a dominant role in inhibiting the transportation of the FHNPs-As(?).Completely aged agricultural organic inputs will strongly inhibit the FHNPs-As(?)transport.When the content of agricultural organic inputs are the same,the FHNPs-As(?)transport under neutral conditions is greater than that under alkaline conditions.