Study On The Mixed Adsorption Characteristics Of Benzene/Naphthalene And Rotary Spray Oxidation Process In Industrial Polluted Soil

As China rapidly urbanizes and upgrades its industries,environmental pollution has become a byproduct of industrial transformation and urban expansion,involving soil contamination,groundwater pollution,wall and equipment pollution,and waste pollution.Among them,polycyclic aromatic hydrocarbon(PAH)pollution is widely distributed.In the soil survey of China in 2014,the rate of exceeding moderate/heavy pollution points was second only to cadmium and DDT,and the average value of PAH in Chinese soil was about 2.96 mg/kg in 2016.PAH pollution has the characteristics of multiple components,difficult degradation,difficult migration,easy volatilization,and high toxicity.Traditional physical remediation techniques are difficult to effectively treat them,so the mechanism of the coexistence of multicomponent pollution in industrial legacy sites and efficient remediation methods are of great research value and engineering significance in the fields of civil engineering and environmental industry.Based on previous research,this study investigated the adsorption process and interaction relationship of mixed components of benzene and naphthalene under equilibrium and non-equilibrium conditions using batch and column experiments,respectively.The dominant factors during non-equilibrium adsorption of benzene and naphthalene were analyzed using a two-domain/two-point model.The optimal oxidation ratio of the carbon-supported zero-valent iron/sodium persulfate(BC-nZVI/PS)combination for the mixed components was determined using orthogonal analysis.In addition,on-site high-pressure spray repair experiments were conducted using micro/nano/carbon-supported zero-valent iron(Fe~0[um]/Fe~0[nm]/BC-nZVI)and sodium persulfate(PS)activated by NaOH,and the repair process of naphthalene was monitored by electrical resistivity tomography(ERT).The migration and transformation laws of the activator during the repair process were studied by comparing the concentration distribution of iron ions and naphthalene in the samples.Finally,a rotating spray jet model was established considering the oxidation and degradation factors based on the two-phase Eulerian-Eulerian theory.The main conclusions obtained in this article are as follows:(1)The quasi-first/second-order kinetic models can accurately describe the adsorption kinetics of the benzene-naphthalene mixture,and the isothermal adsorption process is better fitted by the Freundlich model.The adsorption mechanism of benzene-naphthalene includes hydrophobic partitioning,occupation of adsorption sites on the particle surface,and self-stacking mechanism of naphthalene in the pores,but only occurs in small pores with small disturbances.Under static adsorption conditions,the apparent adsorption relationship between the two is synergistic.(2)Benzene and naphthalene both show faster oxidation degradation rates in soils with smaller particle sizes,and the oxidation curves of pollutants with smaller particle sizes are more similar to the second-order reaction kinetics model.The effects of water-to-soil ratio,Fe0 dosage,and PS dosage on the oxidation reaction were analyzed by orthogonal experiments.(3)The adsorption concentration in the column test is generally lower than that in the batch test.The adsorption amount of benzene and naphthalene increases with the decrease of soil porosity,flow rate,and initial pollution concentration.The synergistic effect of benzene and naphthalene in the pores will be greatly weakened,and the apparent adsorption relationship is competitive.Both the two-region/two-point model can accurately describe the non-equilibrium adsorption process of benzene and naphthalene,and for any component in the mixed adsorption condition,the two-point or two-region model can still be used to describe it.The model analyzes the dominant factors of non-equilibrium adsorption under different working conditions by changing the flow domain ratio and the instantaneous adsorption site ratio.(4)In the on-site spray test,ERT accurately reflected the location of pollution remediation,with a maximum deviation of less than 0.5 m.The resistance change value is positively correlated with the naphthalene remediation value,and there is an error between the estimated pollution remediation value by fitting the curve and the actual remediation value,which is between 15%and 25%.The carbon-loaded iron powder showed good stability and sustained-release performance,and the stable oxidation stage was extended by about 8 h after spray.The predetermined pollution removal rate in the final remediation area was:carbon-loaded iron powder group>nano-iron powder group>micron-iron powder group≈NaOH group.(5)Numerical simulation results show that the bi-Euler model considering oxidation degradation can better simulate the spray jet process.The distribution of peroxysulfate and nano-iron powder in the on-site working conditions simulation results are both greater than the actual measurement values,with an overestimation of about 10%to 20%.The jet radius of high-pressure spray is controlled by the migration of Fe~0.An increase in injection flow rate,soil porosity,and a decrease in iron powder particle size all have a significant impact on the distribution range of the reagent.Notably,the relationship between injection flow rate and distribution radius is nonlinear,and the increase in distribution radius is not substantial under conditions of high injection flow rate.In addition,the increase in soil porosity results in a lower concentration of the reagent under the same injection flow rate conditions,necessitating adjustment of the injection concentration to achieve the optimal oxidation ratio in practical applications.