Study On The Adsorption Of Cr(Ⅵ) By Artificially Cultivated Biological Crusts

Among the many valence states of chromium metal,Cr（VI）is the most toxic,Cr（VI）is easily soluble in water and easily absorbed by the human body,through the respiratory tract,digestive tract,skin and mucous membrane invasion,long-term or short-term contact or inhalation may cause cancer,similarly,Cr（VI）has a lasting harm to the environment.At present,cr（VI）treatment method is mainly biomaterial adsorption method,such as by-products of fermentation process,etc.,biological crusts are a large number of organisms in nature,which have been confirmed to enrich heavy metals such as Cu,Cd,As,but the situation of biocharging enrichment cr（VI）is still unclear.This project mainly studies the adsorption of Cr（VI）by artificially cultivated biological crusts through adsorption tests and hydroponic experiments,and the following conclusions are obtained:（1）The surface of the biocrust is rough,uneven,and the structure is relatively loose, resulting in many gaps.When the biocrust adsorbs Cr（VI）,the cell surface matrix undergoes obvious morphological changes,and the structure is more compact and the surface is relatively smooth.The main elements on the surface of biocrust are C,O and Si.After the biocrust is exposed to Cr（VI）solution,the weight percentage of Cr increases from 0 to 0.12,and the content of Cr in the biocrust increases,indicating that the biocrust The skin has a certain adsorption effect on Cr（VI）.Functional groups exist on the surface of biocrusts,among which C-O,C=O,O-H and hydroxyl groups participate in the adsorption process of Cr（VI）.（2）Under the experimental conditions,the adsorption capacity of biocrust on Cr（VI）and the initial concentration of Cr（VI）were basically linear,and the maximum removal rate of chromium in aqueous solution by biocrust could reach more than 90%.The optimum conditions for biocrust adsorption of Cr（VI）were p H 2（adsorption capacity 0.058mg/g,removal rate 36.41%）,biocrust addition amount of 0.075g/ml（adsorption capacity0.038mg/g,removal rate 36.41%）The initial concentration of Cr（VI）was 10 mg/L（the adsorption amount was 0.058 mg/g,and the removal rate was 36.44%）.Among the effects of coexisting ions selected in this study on the adsorption of biocrusts,Ca²⁺,Na⁺and PO₄^3-ions all increased the adsorption performance of biocrusts on Cr（VI）to varying degrees,and NO₃^-ions had an effect on the adsorption performance of biocrusts is smaller.（3）Under the test conditions,the p H value of the solution at the same Cr（VI）concentration increased with the increase of the amount of biocrust addition,while Eh was the opposite.The Eh value of the solution at the same Cr（VI）concentration It decreased with the increase of biocrust addition.In the treatment group at the same initial concentration of Cr（VI）,the concentration of Cr（VI）in the solution decreased gradually with the increase of the addition amount of biocrust,indicating that the biocrust has an adsorption effect on Cr（VI）.The changes in plant height,fresh weight and root length of rice seedlings in the hydroponic experiment showed that in the treatment groups with the same Cr（VI）concentration,the plant height,fresh weight and root length of rice seedlings in the biological crust treatment group were better than those in the treatment group.No biological crusting treatment group was added,namely 1mg/L Cr（VI）treatment T1<T2<T3,2mg/L Cr（VI）treatment T4<T5<T6,4mg/L Cr（VI）treatment T7<T8<T9.When the addition amount of biological crust was the same,the plant height and fresh weight of rice seedlings decreased with the increase of Cr（VI）concentration（P<0.05）.Treatment group T2>T5>T8,12g biological crust treatment group T3>T6>T9.The difference in root length was not significant,but the root lengths of rice seedlings in the treatment group with biological crusts were all greater than those in the groups without biological crusts.