Study On Remediation And Mechanism Of Fe-Based Amorphous Alloy On Soil Contaminated By Copper Smelting

Smelting and chemical enterprises will cause serious heavy metal pollution to the surrounding soil environment in the production process.Even if these enterprises are shut down or relocated,heavy metals in the soil will exist permanently,causing continuous harm to the local ecological environment.However,most of the traditional remediation methods are extensive operations,which have low restoration efficiency,long cycle,difficult operation,and serious ecological damage.Therefore,it is of great significance to carry out the research on efficient and environmentally friendly remediation materials and processes.In this paper,sandy loam and farmland loam commonly existing around the smelter were selected as remediation objects,and Fe₇₈Si₉B₁₃^APamorphous powder was used as immobilization material to remediate Cu polluted sandy loam by chemical immobilization.The kinetic process of immobilization reaction,the influence of environmental factors on remediation effect,the enhanced desorption of auxiliary reagents,and the application of magnetic separation technology were explored.The Fe₇₈Si₉B₁₃^APpermeable reaction barrier enhanced electrokinetic method was used to remediate the farmland loam irrigated by long-term sewage.A brand-new electric reaction device was constructed,and the electrokinetic reaction process and mechanism were expounded.The main results are as follows:（1）In order to explore the feasibility of Fe₇₈Si₉B₁₃^APapplication in the field of soil remediation,and to clarify the efficiency and reaction mechanism of reduction and immobilization of Cu²⁺by Fe₇₈Si₉B₁₃^AP.Firstly,the comparative experiments of Fe₇₈Si₉B₁₃^APand ZVI immobilized remediation of simulated Cu contaminated soil were carried out under the conditions of different temperature,p H,and dosage of immobilized materials.The results showed that increasing the temperature,properly adjusting the p H value to the weak acid condition,and increasing the dosage of immobilized materials can effectively promote the immobilization of mobile Cu²⁺.In each experiment,the reduction rate of Cu²⁺by Fe₇₈Si₉B₁₃^APwas higher than that by ZVI,and the reaction process accorded with the description of quasi-first-order kinetic equation.The reason is that Fe₇₈Si₉B₁₃^APhas lower apparent activation energy,more negative redox potential,lower valence band top,and a large number of pore structures in the product layer.（2）After determining the immobilization reaction mechanism and remediation efficiency in the simulated contaminated soil,the remediation of the field sampled soil was carried out.Firstly,organic acid leaching pretreatment combined with Fe₇₈Si₉B₁₃^APimmobilization remediation process was used to study the effect of external environment on the desorption of heavy metal ions.It was determined that citric acid was relatively more suitable for leaching the sampled soil.With the increase of citric acid concentration,the ratio of soil to liquid decreases,and the proper extension of leaching time is beneficial to the leaching of heavy metal ions.The leaching mechanism of heavy metals by citric acid in the leaching process is that the adsorbed heavy metals are desorbed by the replacement of H⁺,or the immobilized heavy metals are released by destroying the structure of iron and manganese oxides by H⁺.After that,the heavy metal ions complexed with citrate to form soluble citrate.The leaching reaction accords with Elovich equation and belongs to heterogeneous diffusion process.On this basis,citric acid+Fe₇₈Si₉B₁₃^APmixed suspension was used for leaching and reduction of heavy metals in soil at the same time,and then the residual Fe₇₈Si₉B₁₃^APand its immobilized heavy metals attached to its surface were extracted by magnetic separation process.The results show that the magnetic separation of Cu,Pb and Ni can be improved by increasing the concentration of citric acid,the oscillation speed,and the amount of Fe₇₈Si₉B₁₃^AP.Finally,the optimum conditions were determined as follows:the oscillation speed was 250 r/min,the Fe₇₈Si₉B₁₃^APdosage was 50 mg/g,and the citric acid concentration was 50 mmol/L.Under these experimental conditions,the magnetic separation rates of Cu,Pb,and Ni were 54.3%,45.8%,and 40.2%,respectively.After a long time of simulated acid rain leaching,the release of Cu,Pb and Ni was extremely low,and most of the unextracted heavy metals could exist stably in the soil.（3）For the farmland loam with high viscosity and poor permeability around the smelter,the electric method is more suitable to be remedied.When a low voltage electric field is applied at both ends of the contaminated soil,the fixed metal is first leached under the action of acid electrolyte desorption,and then removed from the soil by electrokinetic action such as electromigration and electroosmotic flow.In the comparative experiments of traditional electrokinetic method（EK）,ZVI permeable reaction barrier enhanced electrokinetic method（ZVI-EK）,and Fe₇₈Si₉B₁₃^APpermeable reaction barrier enhanced electrokinetic method(Fe₇₈Si₉B₁₃^AP-EK)to remediate simulated Cu contaminated farmland loam,the removal rate of Cu in Fe₇₈Si₉B₁₃^AP-EK was much higher than that of the other two groups,reaching 57.5%.The reason is that the existence of cathode Fe₇₈Si₉B₁₃^APcan reduce and immobilize the Cu²⁺which migrates to the cathode in time,which eliminates the accumulation of Cu²⁺in the cathode and promotes the subsequent electromigration process of Cu²⁺.Then,the Fe₇₈Si₉B₁₃^AP-EK electrokinetic reactor was optimized.The electrolyte was a mixture of citric acid and Mg Cl₂.Citric acid can promote metal leaching,while Mg Cl₂can increase the conductivity of electrolyte.Due to the existence of PRB,the electrolyte can be refluxed between cathode and anode.After immobilization of PRB and cathodic plating,the reflux solution will not pollute the anode soil again.The carbon nanotube modified foam copper electrode(CNT-Cu ^PM)with large specific surface area and good conductivity is selected as the electrode material,which can effectively improve the current intensity.（4）Using the optimized reactor to treat the actual contaminated soil,the optimum experimental conditions were obtained by orthogonal experiment:the voltage gradient was 3 V/cm,the concentration of citric acid was 50 mmol/L,and the water content was 40%.The influence of voltage gradient on the metal removal rate was highly significant,and other factors were significant.Under these conditions,the removal rates of Cu,Pb,Ni,and Cd were 55.3%,62.2%,48.5%,and 68.2%,respectively.（5）Intermittent power supply（power on for 18 h/power off for 6 h,power on for 12h/power off for 12 h）was tried to reduce the power consumption in the process of electrokinetic remediation,and the effects of power-off frequency on current,soil p H,and heavy metal removal were analyzed.According to the energy consumption estimation model,when the electrification time was shortened from the whole electrification time to 3/4 and 1/2 electrification time,the total energy consumption decreased by 36.81%and 63.58%,while the removal rate of target metal only decreased by about 2%and 6%,respectively.This is due to the fact that the immobilized metal continues to dissolve during the power-off period,which is beneficial to destroy the concentration balance established in the electrokinetic reaction and ensure the rapid migration of metal ions to the cathode during the electrification period.