Application Of The Combination Of Compost Products And Attapulgite In Remediation Of Cadmium Contaminated Soil

Passivation remediation technology has become one of the hot technologies in the field of remediation of light heavy metal pollution in large areas in recent years because of its advantages of fast remediation efficiency,convenient operation and economy.At present,it has been proved that attapulgite alone and compost alone can be used to remediate heavy metal contaminated soil.However,fulvic acid in humus of compost alone can activate heavy metals in soil to a certain extent,reducing the passivation effect of compost on remediation of heavy metals,which limits their application in passivation remediation of heavy metals in soil.In the composting process,different native biomass,humification conditions and humification degree will cause differences in chemical composition,functional groups and structure of humus.In addition,attapulgite has a special chain layered structure,with the characteristics of large specific surface area and strong adsorption capacity,and can be combined with compost products to form humus-inorganic mineral-heavy metal ternary compound.Therefore,the difference of humus in different compost products will affect the complexation and chelation between humus,heavy metals and attapulgite in compost products or among them,which is very important for the success or failure of soil heavy metal passivation and remediation.Therefore,it seems to be a more effective way to passivate soil heavy metals and improve soil physical and chemical properties by combining compost products with attapulgite to complement each other’s advantages.However,the passivation effect and mechanism of composting products combined with attapulgite on cadmium contaminated soil are still unclear.Therefore,more evidence is still needed to prove the feasibility of the application of composting products combined with attapulgite to passivate and repair cadmium contaminated soil.In this study,four different compost materials（Pig manure:straw=1:1;Pig manure:straw:bean dregs=4.5:4.5:1;Pig manure:straw:tea=3:3:2;Pig manure:straw:bean dregs:tea=4:4:1:1）,and four different compost products and attapulgite were used to passivate and repair cadmium contaminated soil（the addition amounts of compost products alone,attapulgite alone,four different compost products and attapulgite combined treatment were 2%,2%and 1%+1%respectively）.The effects of different compost products combined with attapulgite on soil fertility,soil enzyme activity and other soil qualities were systematically evaluated,and the effects of compost products combined with attapulgite on cadmium passivation and cadmium enrichment of cabbage were studied,which provided theoretical and scientific basis for cadmium contaminated soil treatment.The main research results are as follows:（1）The p H,electrical conductivity,organic matter,total nitrogen,total potassium,dissolved organic carbon,available nitrogen,available phosphorus and available potassium of the soil treated with compost and attapulgite increased significantly（p<0.05）.Compared with no treatment（CK）,all treatments with soil passivator increased p H by 0.07-1.94,soil conductivity by 0.07-0.19 ds.m^-1,and 1%attapulgite and 1%composting products with pig manure:straw:bean dregs=4.5:4.5（C2+A）and 1%compost were added.Compared with attapulgite alone,when four compost products are combined with attapulgite,the dissolved organic carbon,alkali-hydrolyzable nitrogen,available phosphorus and available potassium increase by 4.65-25.41 ml.l^-1,0.1-2.8 mg.kg^-1,0.19-0.31 mg.kg^-1 and 45.77-61.66 mg.kg^-1respectively.It can be seen that compost products combined with attapulgite can increase soil nutrients.（2）The influence of different compost products combined with attapulgite on the enzyme activity of soil remediation was comprehensively expounded.Compared with CK,each treatment had a certain inhibitory effect on phosphatase,urease increased by 1.24-2.16times respectively,and C2+A had the most significant effect on urease activity.Compared with CK,sucrase and catalase increased by 1.02-2.93 times and 2.42-3.31 times respectively.（3）Compared with CK,the content of Ca Cl₂-Cd in all treatments decreased by 30.65%-96.47%respectively,and the content of Ca Cl₂-Cd in C2+A treatment decreased by 96.38%.All treatments reduced the contents of acid-soluble cadmium and reduced cadmium,and the proportion of oxidized cadmium changed little,but increased the content of residual cadmium.C2+A treatment significantly reduced acid soluble state by 6%,reduced state by4%and residue state by 7%.It can be seen that compost combined with attapulgite is more beneficial to passivate soil cadmium.（4）In this experiment,the Fourier transform spectrum and scanning electron microscope of the soil before and after the optimal treatment of C2+A passivation repair were compared.Scanning electron microscope images show that,compared with the original soil,there are a lot of particles on the surface of the soil after C2+A remediation.FT-IR spectra further show that in the functional group region,some characteristic peaks are shifted,the peak intensity is enhanced,and a new single peak is formed.To sum up,it is speculated that the active functional groups of compost products and attapulgite,such as carboxyl and hydroxyl,react with cadmium in soil through adsorption,complexation,interlayer ion exchange,co-precipitation,etc.,or form ternary complexes among attapulgite,humus and cadmium,thus forming particles on the soil surface and enhancing the precipitation of cadmium.（5）The effects of different compost products combined with attapulgite on the growth and cadmium content of edible parts on the ground of plants were evaluated.Pot experiment showed that,compared with CK,the fresh weight of edible part of Chinese cabbage in all treatments increased by 1.18-2.97 times,the cadmium content decreased by 0.12-0.32 mg.kg^-1,and the bioaccumulation decreased by 0.09-0.24.Among them,in C2+A optimal treatment group,the fresh weight of edible part of Chinese cabbage increased by 2.97 times and the cadmium content of edible part decreased by 0.32 mg.It can be seen that the combination of compost products and attapulgite is more beneficial to increase the fresh weight of the edible part of Chinese cabbage,reduce the cadmium content of the edible part of Chinese cabbage and reduce the bioconcentration factors.