Study On Removal Of Lead From Soil By Potassium Ferrate Assisted Plants

As a big coal province,Shanxi has many mines and a large area of coal mining waste,which leads to soil heavy metal pollution.Lead is the main heavy metal in the soil of the mining area,which will permeate into the aquifer and contaminate the groundwater,thus reducing the water quality of water resources and endangering human life and health.Therefore,the remediation of lead-polluted soil in mining area is an urgent problem.The in situ fixation of soil pollutant Pb²⁺,which is taken out by plants when conditions permit,is an effective means to prevent its further contamination of groundwater.In order to study the technical problem that how to fix heavy metals in soil polluted by coal in situation.This paper used soil(lead content 8 mg·kg^-1)and Pb（NO₃）₂(50-400 mg·L^-1)do adsorption experiment of the original soil and the soil added K₂Fe O₄,and studied the adsorption law of lead on two kinds of soil and carried out the kinetic analysis.Besides,static leaching experiment and continuous leaching were also carried out by simulating acidic rainwater.Thus,the effect of K₂Fe O₄on strengthening adsorption and fixation of lead in soil was investigated from two aspects:leaching concentration and the effect of soil on adsorption state of lead.As the research plant to lead absorption,respectively in a hydroponic condition and soil culture condition of sainfoin,green bristlegrass,alfalfa,ryegrass,sunflower five plants screening experiment,measure its plant agronomic traits,such as the germination rate,root length,shoot length,fresh weight and dry weight and five kinds of plant uptake of lead,and calculation of five kinds of plants for the repair rate of lead.The effects of lead on absorption by ryegrass and sunflower under different initial concentrations of Pb²⁺,different p H values,different humidity and different incubation periods were investigated by using the soil culture and screening experiment with potassium ferrate.According to the experimental research,the conclusions are as follows:（1）The addition of potassium ferrate can significantly improve the adsorption effect of soil on lead.The contaminated soil(with the content of lead of 8 mg·kg^-1)still has a good adsorption effect on Pb²⁺with the initial concentration of 350 mg·L^-1.When the Fe/Pb mass ratio is 5 and the adsorption time is 8 h,the adsorption amount is up to 486 mg·kg^-1.The adsorption process is not sensitive to p H and temperature.（2）The adsorption isotherm of soil lead conforms to the Langmuir equation;After potassium ferrate was added,the adsorption isotherm of lead in the soil was in line with the Freundlich equation,and the reaction was in line with the quasi-second-order kinetic model,indicating that the adsorption of lead changed from single-layer adsorption to multi-layer adsorption,and the physical adsorption changed to physicochemical adsorption,and the enhanced adsorption effect was significant.（3）Through the determination of agronomic traits of five plants,the results showed that ryegrass had the highest germination rate,longer bud length,longer root length,and developed roots;The shoot length and root length elongation were the best in two cultivation conditions.The fresh and dry weights of ryegrass and small sunflower were also the best,so that the accumulated biomass was also the best.The lead removal rates of five plants under hydroponic and the soil culture conditions were in the following order,ryegrass>alfalfa>sunflower>red bean grass>dogtail grass,sunflower>ryegrass>alfalfa>red bean grass>dogtail grass.Therefore,ryegrass and sunflower were selected as experimental crops in the plant screening section.（4）Ryegrass and sunflower was cultured in soil treated with potassium ferrate.Ryegrass and sunflower had the best absorption effect on lead when the Fe/Pb mass ratio were 4、5.The humidity were 15.3%、20.5%（each watering were 10、15 m L）.When the culture period was 30 days,and the absorption amount of ryegrass was as high as1.307 mg·g^-1.When the culture period reached50 days,the absorption amount was as high as 1.361mg·g^-1,but the absorption amount of lead to sunflower was still increasing.The phytoremediation process is also insensitive to p H due to the buffering properties of the soil.（5）When the initial lead content in the soil is too high,lead will produce toxic effect on plants,so that the growth of plants will be stressed.Compared with the two plants,the toxic effect of lead on sunflower was less,that is,sunflower’s tolerance to lead was more prominent.（6）Potassium ferrate was added to stabilize the adsorption of lead in the soil,so as to reduce the leaching behavior of lead and prevent groundwater pollution caused by leaching of lead in the soil.The presence of potassium ferrate will change the existing form of lead in soil and increase the removal rate of lead by plants;However,the presence of potassium ferrate can also delay the time of germination and inhibit the growth of plants.The study in this paper has important practical value for in-situ remediation of lead contaminated soil.