Study On Three Soil Amendments Enhanced Ryegrass Remediation Of Copper And Cadmium Contaminated Red Soil

Phytoremediation has been widely studied at home and abroad for its low cost and environmental friendliness.The red soil in Jiangxi is acidic,with poor water retention and lack of phosphate fertilizer and organic fertilizer,which is not conducive to plant growth.In order to solve the above problems,this study selected three environmentally friendly amendments:attapulgite?clay mineral?,struvite?phosphorus material?,and DOM?organic matter?as remediation materials.The amendments were prepared,extracted and characterized,and the mechanism of the amendments interaction with Cu and Cd was analyzed.Ryegrass with large biomass and short growth cycle was selected as the test plants.Pot experiment was conducted to study the effects of the three modifiers on the growth and tolerance of the tested plants,the absorption of Cu and Cd,and the effects on the rhizosphere soil under different soil pollution types,so as to clarify the mechanism of the modifiers to enhance the resistance to heavy metals and phytoremediation efficiency of plants.In addition,the use of functional composite concept,the combination of attapulgite,struvite and DOM soil modifiers with different functions were combined with ryegrass to remediate Cu and Cd contaminated soil,and the best remediation mode to promote plant growth and improve phytoremediation efficiency was determined.In order to provide theoretical and experimental basis for the remediation of heavy metal contaminated soil with the combination of modified agents and phytoremediation.The main research results were as follows:1.In order to improve the adsorption performance of attapulgite,the attapulgite had been subjected to thermal modification,acid modification and biomass modification.The effect of modified attapulgite on soil adsorption and desorption of Cu and Cd and the effect of soil Cu and Cd dynamic leaching were studied.The results showed that the adsorption capacity of soil for Cu and Cd under the treatment of modified attapulgite increased by 3.45%?9.93%and 19.37%?36.38%,respectively.Modified attapulgite could effectively reduce the mobility of Cu and Cd in the soil and reduce the risk of groundwater pollution.Among them,thermally modified attapulgite has the best passivation effect.The adsorption mechanism of Cu and Cd was analyzed through the isotherm adsorption model and FT-IR and XRD characterization of the adsorption products.The results showed that the adsorption of Cu and Cd by thermally modified attapulgite was mainly heterogeneous adsorption of multi-molecular layers.It mainly occured on the surface of the material,and it was coordinated with Cu and Cd through the silicon hydroxyl group.2.With magnesium chloride as additive,the ratio of n(Mg²⁺):n?NH₄⁺?:n(PO₄^3-)in N and P wastewater was adjusted to be 1.15:1:1,p H was between 8.5and 9,and the reaction time was 30min.The resulting products were characterized by SEM,FT-IR and XRD,indicating that struvite was the main product.The effect of struvite on red soil was studied,and the results showed that struvite could increase the soil p H to promote the adsorption of Cu and Cd by soil colloids,at the same time increase the soil phosphate ion content to promote Cd₅?PO₄?₃?OH?precipitation with Cd,and other methods to reduce the biological availability of Cu and Cd.3.By comparing the infrared,ultraviolet,and three-dimensional fluorescence spectra before and after the reaction of DOM extracted from Carex with Cu and Cd,it was shown that the DOM extracted from Carex grass had a large number of functional groups such as hydroxyl,carboxyl,carbonyl,and methyl groups.The main components were humic acid with relatively large molecular weight.Carex DOM mainly produced complexation with Cu and Cd through functional groups such as carboxyl and hydroxyl groups of fulvic acid-like substances and humic acid-like substances in the ultraviolet region.After the reaction,the number of unsaturated conjugated double bond structures of Carex DOM,The level of humification and the number of substituents on the aromatic ring decreased significantly.The effect of Carex DOM on soil adsorption of Cu and Cd was studied.The results showed that Carex DOM would reduce the maximum adsorption capacity,adsorption equilibrium rate and adsorption affinity of soil to Cu and Cd.4.The effects of thermally modified attapulgit(5,20,50 g·kg^-1),struvite(10,50,100 g·kg^-1)and Carex DOM(250,500,1000 mg·kg^-1)on the growth of ryegrass in soils with different pollution levels were studied.The results showed that:?1?Thermally modified attapulgite,struvite,and DOM had obvious growth-promoting effects on ryegrass.Among them,thermally modified attapulgite and struvite could reduce the MDA content of ryegrass leaves and reduce the degree of membrane lipid peroxidation;Struvite and DOM could promote the production of GSH from ryegrass leaves and eliminate the negative effects of free radicals.?2?The three amendments had a promoting effect on soil enzyme activity.However,thermally modified attapulgite had no significant effect on soil invertase activity.In low-pollution and high-pollution soils,high doses of Carex DOM(1000 mg·kg^-1)could inhibit soil urease and invertase activities.?3?Thermally modified attapulgite could reduce the number of soil bacteria and increase the number of fungi and actinomycetes;DOM would reduce the number of soil actinomycetes and increase the number of soil bacteria and fungi;struvite could promote the activity of three soil microorganisms.?4?Thermally modified attapulgite and struvite could increase the total amount of Cu and Cd per unit mass of ryegrass by increasing the biomass of ryegrass.DOM could promote the growth of ryegrass and increase the enrichment coefficient of Cu and Cd in ryegrass leaves and improve the remediation efficiency.When the additive dosage of thermally modified attapulgite was 20 g·kg^-1,the remediation efficiency of ryegrass was the best;struvite could only increase the total extraction amount of Cu and Cd by ryegrass in highly polluted soil.The remediation efficiency was the best when the amount was 50 g·kg^-1,which increased the total extraction amount of 59.8%Cu and44.27%Cd,respectively;when the dosage of Carex DOM was 500 mg·kg^-1,the remediation effect was the best,In low-polluted soil and high-polluted soil,the Cu content of ryegrass leaves was increased by 71.7%and 22.5%,respectively,and Cd content of ryegrass leaves was increased by 92.1%and 46%,respectively.5.The combined effect of thermally modified attapulgite(20g·kg^-1),struvite(50g·kg^-1),and carex DOM(500mg·kg^-1)on highly contaminated soil was studied under the optimal additive dosage.The results showed that:The treatments of various combination modifiers could play a combined role,promote the growth of ryegrass in Cu and Cd contaminated soil,promote the activity of soil microorganisms and enzymes,improve the soil environment,increase soil fertility,and improve remediation effectiveness.Among them,The treatment of thermally modified attapulgite+struvite+carex DOM had the best effect on soil environmental quality improvement;The thermal modified attapulgite+struvite treatment showed the best growth status,and the biomass of ryegrass increased by 260.15%compared with the blank treatment;Ryegrass had the highest remediation efficiency of Cu and Cd in the treatment of struvite+carex DOM,which was improved by 55.52%Cu extraction and83.29%Cd extraction relative to the blank treatment.