Experimental Study On Remediation Of Biochar In Typical And Mercury Contaminated Farmland Soil

With the problem of mercury pollution soil in farmland is expanding continuously and the intensification of pollution,the remediation of heavy metal mercury contaminated soil has become the primary task of the society,and mercury pollution has become a hot spot of research.However,due to the characteristics of mercury,long term stay in the soil,microorganisms can not be degraded,there is no suitable repair technology at present.Biological carbon material has the characteristics of high specific surface area,rich oxygen functional group and high pH value.It is suitable for heavy metal adsorption and passivation materials.It has the advantages of outstanding adsorption effect,low production cost and utilization of solid waste resources.It can also be used as soil modifier to improve soil fertility and water holding capacity.We use biosorption materials to study mercury contaminated farmland.In this study,the two farmland soils of Aozhai and the Hetaoshu Village,town of Wanshan mining area in Guizhou was treated as the target of remediation.The biochar prepared from different raw materials those was selected as passivation material.Firstly,the basic characterization of biochar structure was carried out.The effects of different biochars on the basic physical and chemical properties of soil and the adsorption law of effective mercury were studied by soil culture experiment and potted Chinese cabbage,and the parabolic diffusion equation,Elovich equation,weight function equation,Freundlich modified formula and exponential square were used.The correlation between the effective state of soil mercury and the proportion of soil pH and biological carbon,the correlation analysis between the effective state of the soil mercury and the mercury content of the root,stem and leaf of Chinese cabbage and the sum of the two,and the analysis of the factors of reducing the mercury content in the plant with the characteristics of the biological carbon materials;Based on two indicators of mercury content in the object,walnut shell biochar was finally screened out.In order to understand the stability of the adsorption of heavy metal mercury by the biochar,soil leaching experiments were carried out.Through the above experimental analysis,the following main conclusions are obtained.1.The pH value of 5 biochars of pepper straw,rice husk,walnut shell,pine wood and rice pole are above 8,showing different alkalinity.The pH value of coconut shell biochar is about 4.35,and them contain two elements of C and O,the content of C is basically 70% to 90%,and the content of O is basically distributed in 5% to 20%,the oxygen of pepper straw and rice husk.The element content is higher than that of other raw materials,the reason is the rich oxygen group,the walnut shell and coconut shell biological charcoal have micropore and large specific surface area.The infrared spectrum shows that different types of biological charcoal have approximately the same types of surface groups,mainly containing-OH,-C-H,pepper and rice straw two straw.The number of biological carbon containing C-O-C is relatively large.2.(1)The pH value of two types of soil is related to the type and proportion of biochar added.Among them,the pH(about 0.35 to 1.15 units)could be significantly increased by chilli bio carbon.The coconut shell carbon had no effect on the soil pH,and the pH value increased with the increase of the proportion of adding.(2)the effect of six biochar on the effective Hg of soil polluted by high and low concentration mercury,the better the adsorption effect with the increase of culture time.In the same proportion of biological carbon,walnut shell biochar decreased the effective rate of mercury,and the maximum rate of reduction was 97.14%(7%)when it was cultured to 100 days.The content of effective Hg in the two soils treated with coconut shell carbon has no correlation with the proportion of carbon added and soil pH,and the treatment of the other carbon has a better negative correlation.3.(1)Potted experiment data showed that biochar input improved plant growth conditions,increased crop yields,and significantly increased soil pH and organic matter content.Compared with the blank group,the growth of biochar in walnut shell soil increased 10.2 times(3% content)and 12 times(5% content)compared with the blank group.In the two soils,chilli straw charcoal significantly increased soil pH,and pine carbon had the greatest influence on soil organic matter.(2)six kinds of biological charcoal can reduce the content of mercury in plants.The 5% addition ratio of walnut shell charcoal is the best,the high concentration root reduction rate is 60.13%,the stem and leaf decrease 64.86%,the low concentration root is 70.37%,and the stem and leaf decrease 78.02%.Coconut shell charcoal followed by high concentration of roots decreased by 52.53%,stems and leaves decreased by 61.38%,low concentrations of roots 54.95%,stems and leaves decreased by 67.03%.The reduction rate of the other four kinds of carbon with high concentration was 27%.22 to 40.51%,the stem and leaf decreased from 37% to 50%,the low concentration was 40% to 50%,and the stem and leaf decreased by 40% to 46%.In addition,there was a positive correlation between soil available Hg and mercury content in Chinese cabbage.4.soil column leaching experiments showed that,under the leaching conditions of pH=3.5’s forest solution,the pH of the addition of 5%HTKBC was improved,and the balance between the adsorption and desorption of mercury in the soil and the release of mercury in the soil showed that the HTKBC had a stable adsorption in the remediation of the soil contaminated by mercury and passivation of the mercury element in the soil.The fruit is better.