Adsorption Characteristics Of Cadmium And Copper By Modified Biomass Materials And Effect On The Uptake By Brassica Chinensis L.

Cadmium pollution and copper pollution in the soil are often associated.At present,the research on cadmium and copper pollution remediation mainly focuses on the development of efficient adsorption materials for single polluted water and the exploration of adsorption mechanism,while the research on the remediation of cadmium and copper composite contaminated soil is relatively few,and the existing research on adsorption passivation materials often limited to various types of biomass charcoal and its derivatives,and attention to biomass such as agricultural waste is rare.Thus,with the goal of "using waste to control pollution",nine kinds of modified biomass were prepared by chemically modifying the biomass of cheap agricultural waste:rice straw(RS),rice husk(RH)and sugarcan bagasse(SB)biomass.The succinic anhydride modified rice husk(S-RH)and sodium hydroxide modified rice husk(NaOH-RH)were obtained through the screening of cadmium and copper adsorption equilibrium tests.Combined with SEM,FTIR,XPS and other characterization methods,the surface characteristics of the material were explored,and its adsorption potential for cadmium and copper was revealed.The incubation experiment verified the regulation effect of S-RH and NaOH-RH on soil cadmium and copper availability.On this basis,we further studied the application potential of NaOH-RH to reduce the uptake of cadmium and copper in Brassica chinensis L.by pot experiment.The main findings are as follows:(1)Effects of modification methods on the adsorption of cadmium and copper by biomass materials.The adsorption equilibrium test found that among the three modification methods,the succinic anhydride modification method has the best effect on improving the biomass adsorption capacity,followed by sodium hydroxide modification,while the succinic acid modification method has almost the same capacity for biomass adsorption.no effect.The modification of succinic anhydride can effectively improve the adsorption performance of biomass to Cd(?)and Cu(?).The removal rate of S-RH to Cd(?)(50 mg L-1)can reach 83.5%,and the removal rate of Cu(?))(100 mg L-1)removal rate can reach 38.2%,which is 2.0 times and 3.7 times of RH removal rate of Cd(?)and Cu(?),respectively.Sodium hydroxide modification method can effectively improve the adsorption performance of rice husk to Cd(?)and Cu(?).The removal rate of Cd(?)in solution by NaOH-RH is 1.6 times that of NaOH-RS and NaOH-SB,respectively And 3.5 times,the removal rate of Cu(?)in the solution is 1.3 times and 2.5 times that of NaOH-RS and NaOH-SB,respectively.(2)Surface characteristics of S-RH and NaOH-RH and their adsorption characteristics for cadmium and copper.After modification,the specific surface area of S-RH and NaOH-RH is greatly improved;SEM results show that the surface of NaOH-RH is rough,and S-RH has a layered structure;FITR results show that the surface of NaOH-RH is rich in active hydroxyl groups,and S-RH contains ester bonds and carboxyl groups.NaOH-RH and S-RH can adsorb Cd(?)and Cu(?)through physical adsorption,ion exchange and complexation of oxygen-containing functional groups on the surface.The adsorption of Cd(?)and Cu(?)by S-RH and NaOH-RH follows a pseudo-second-order kinetic equation.The Langmuir isotherm adsorption model can better describe the adsorption process of Cd(?)and Cu(?)by S-RH and NaOH-RH.The maximum adsorption capacity of S-RH for Cd(?)and Cu(?)is 160.32 mg g-1 and 20.76 mg g-1,respectively.The maximum adsorption capacity of NaOH-RH for Cd(?)and Cu(?)were 18.18 mg g-1 and 9.21 mg g-1,respectively.(3)The effect of S-RH and NaOH-RH on soil cadmium and copper availability.Apply S-RH and NaOH-RH into the soil at a mass ratio(0.7%),which is close to the actual amount of agricultural waste returned to the soil,and compare the effects of the materials on the effective cadmium and available copper content in the soil after 1 day and 30 days of incubation.The study found that the passivation effect of NaOH-RH on soil cadmium and copper is better than that of S-RH.NaOH-RH can reduce the effective cadmium content in the soil by 23.43%,but has no significant effect on the available copper in the soil;while S-RH has no significant effect on the effective cadmium and available copper content in the soil.The effectiveness of soil cadmium and copper in incubation experiment is dominated by changes in soil Eh and soil pH.After S-RH is applied to the soil,oxygen-containing functional groups such as hydroxyl and carboxyl groups on the surface are combined with iron oxide in anaerobic soil environment.The complexation of soil cadmium and copper is limited;and NaOH-RH in the soil environment through its rich active hydroxyl groups and soil cadmium complex,thereby reducing the effectiveness of soil Cd(?).(4)The effect of NaOH-RH on the uptake of cadmium and copper by Brassica chinensis L.NaOH-RH was added to the cadmium and copper compound contaminated soil at two different dosages to conduct pot experiments.It was found that NaOH-RH had a significant effect on reducing the effective cadmium and effective copper content in the soil,and high-dose application on the soil cadmium and copper.The passivation effect is better than low dose.Applying NaOH-RH at a mass ratio of 1%reduced the effective cadmium and available copper contents in the rhizosphere soil of Brassica chinensis L.by 91.39%and 66.59%,respectively,and the effective cadmium and available copper contents in the non-rhizosphere soil decreased by 66.01%and 67.78%,respectively.When harvested,the cadmium content in different parts of Brassica chinensis L.was in the order of leaf>root>stem,and the copper content in the order from high to low was root>leaf>stem.Adding NaOH-RH can significantly reduce the content of cadmium and copper in various parts of Brassica chinensis L.Applying NaOH-RH at a mass ratio of 1%reduces the cadmium content in roots,stems and leaves of vegetables by 64.64%,53.24%and 69.49%,and the copper content by 54.90 respectively%,45.56%and 71.00%.