Study On The Repair Of Lead-Cadmium Compound Contaminated Soil By New Silicon-Aluminum Composites

With the rapid development and urbanization in recent years,a lot of pollution has been produced in China,including setting up many large factories and factory b uildings,building numerous shopping malls,getting rid of the exhaust gas,waste wa ter and waste residue from mining,printing and dyeing plants,and sewage irrigation in agriculture,etc.Both will pollute China’s atmosphere,water and soil resources,a nd bring harm to the growth and development of humans,animals and plants in Chi na.At present,there are many methods for soil heavy metal repair at home and abr oad,including in situ short-term repair technology.Apparently,all of these not only pollute the atmosphere,water and soil resources,but also hinder the development of human beings,animals and plants in our country.Thus,by adjusting the fly ash（F ly ash-FA）with appropriate alkali,it was set to be modified with NaOH in different ash-alkali ratio and temperature to obtain the new silicon aluminum material（Inter mediate place-IP）.The preliminary screening was carried out,and the determination of properties and surface characterization of SEM-EDS,specific surface area,FTIR a nd XRD had been completed.Meanwhile,the kinetic adsorption of Pb²⁺and Cd²⁺in artificial simulated wastewater has been finished,including the influence of pH,star ting mass concentration and adsorption time on its adsorption performance,which w as explored by kinetics and isotherm model.The soil was polluted by artificially ex ogenous Pb and Cd to the soil culture test and Solanum nigrum-pot experiment to i nvestigate the effects of materials on the effective state of heavy metal DTPA in soi l,the biomass and above-ground transportation of plant Solanum nigrum L.and the changes of activities of Alkaline phosphatase and urease.Provide theoretical basis fo r the application of new silicon-aluminum intermediate materials,The following main conclusions were drawn:（1）Characterization of IP4 by calcination at a ratio of ash to base 1:2 at 250°C for 2hours,the specific surface area is 18 times than FA’s;and the particle size is smaller,the range of mesoporous material is 2.2-60.7μm;after modification,SiO₂/Al₂O₃ is 1.02,which enhances the adsorption performance;in addition,the peaks of Si-O and Al-O is also enhanced in modified IP4 with new functional groups and new coordination polymers,electronegative reactive groups appearing;In the adsorption test of IP4,with the adsorbent dosage is 0.05 g,which is the solid-liquid ratio is 1 g/L,when the adsorption temperature is 25°C,the mass concentration of Pb²⁺and Cd²⁺is 150 mg/L and 100 mg/L respectively,the adsorption equilibrium is basically reached after 30 minutes;the adsorption speed of Pb²⁺by IP4 is faster than Cd²⁺,which shows that IP4 has better affinity for Pb²⁺;the adsorption of IP4 to two ions is affected by solution pH,initial concentration of heavy metal ions and dosing amount,when pH=5 and solid-liquid ratio is 1 g/L,the removal rate of Cd²⁺and Pb²⁺by IP4 is 74.21%and99.03%respectively,In the kinetic analysis and isothermal adsorption model,The adsorption mechanism of IP4 on Pb²⁺and Cd²⁺accords with quasi-secondary kinetics and Freundlich model,there is chemical adsorption of ion exchange exist;（2）In the experiment of soil culture,with adding FA-1.5%and IP4-1.5%,after 60 days of passivation,the effective Pb and Cd in the soil have been passivation repaired,which change the physical and chemical properties of the soil and reduce the toxic rationality of heavy metal,the activities of the two enzymes has increased.The pH increase of the soil was more obvious under the treatment of IP4-1.5%,which was 0.74 units higher than the CK`s pH=7.32;when the dose of IP4 added is 1.5%,the effective state of Pb and Cd in soil decreased by 38.82%and 83.68%respectively,and the effect of IP4-1.5%is the best;（3）Under the condition of sunflower potted plant,the available state of Pb and Cd in soil decreased compared with Control group CK after 60 days of combined application of passivator,and with the addition of the amount of FA and IP4 from 0.5%to 1.5%,the reduction of effective state also increase,the processing effect of IP4 is better than FA.When the addition of IP4 is 0.5%,1%and 1.5%,the Pb and Cd in available state has decreased by 23.92%,25.23%,31.95%and 64.97%,72.17%,83.69%,respectively;（4）Plant Solanum nigrum L.with good tolerance to heavy metals in Pb and Cd combined with contaminated soil with different additional treatment of FA and IP4,after 60days passivation test,the biomass of Solanum nigrum L.has increased;when IP4 is added1.5%,compared with the control,the biomass increased most significantly.The aboveground part has more enrichment of Cd and more Pb in the lower part.After 60 days,the dry weight of both aboveground and underground parts of Solanum nigrum have increased;and under IP4 treatment,the increment is bigger than FA;（5）Under the two experimental forms,the activities of both urease and phosphatase have recovered,and the sensitivity of urease activity to heavy metals in soil was stronger than phosphatase.The lower the content of heavy metals in available state,the more obvious the recovery of enzyme activity is.In short,it can be seen that the modified new silica-alumina composite material after experimental research shows good adsorption performance for Pb²⁺and Cd²⁺in wastewater;it can effectively reduce the effective content of Pb and Cd in soil experiments and increase Plant biomass that promotes the transport of plants from the soil to the aerial parts of plants.Therefore,the alkali-modified silica-alumina composites studied in this paper have certain value in the field of soil heavy metal repair.