The Study On Adsorption And Immobilization Of Cadmium And Copper By Biochar

As the environmental pollution hazard caused by heavy metals becomes increasingly prominent, the abatement of heavy metal pollution has become a research focus at present. Biochar is a kind of charcoal rich in carbon made from rejected biological materials in anaerobic and temperature limiting conditions. Due to its precise pore structure and unique surface chemical property as well as low cost and good workability, biochar is widely employed in the remediation and abatement of heavy metal pollution. The research contents of this paper:preparation and representation of biochar; characteristics of biochar’s adsorption for cadmium ions and cupric ions in aqueous solution; effect of biochar’s adsorption for cadmium ions and cupric ions in soil in pot experiment; effect of biochar’s passivation of cadmium and copper pollution in soil in field experiment.Carbonized it for2h to prepare camphorwood charcoal and cotton straw charcoal separately at300℃and350℃, purchase wheat straw charcoal, peanuthull charcoal, rice straw charcoal, bamboo charcoal, wood charcoal and activated charcoal to make a characterization analysis on the ash content, productive rate, pH value, surface functional groups and porosity of the above materials; use the characteristics of the adsorption of such4biochars as wheat straw charcoal, peanuthull charcoal, wood charcoal and activated carbon activated charcoal for heavy metal pollutants Cd2+and Cu2+in water solution at different concentrations, adsorption times, pH values and dosages; in pot experiment, add Og-kg-1,20g-kg-1,50g-kg-1and100g-kg-1charcoals to the soil contaminated by Cd and Cu as adsorbents, and then research and analyze the change of soil pH, the total amount of heavy metals Cd and Cu, the law of effective state change, and the change of the accumulation of pakchoi dry substance and nitrate content before and after the charcoals are added, to make a preliminary assessment on the remediation effect of biochar on contaminated soil; choose a piece of farmland contaminated by Cd and Cu in Daye City, Hubei Province, for field experiment, and design4charcoal application treatments such as0kg-Chinese acre-1,30kg-Chinese acre-1,60kg-Chinese acre-1, and90kg-Chinese acre-1, to compare the full dose of Cd and Cu in the soil treated in different ways, the content of Cd and Cu in four chemical forms and the content of Cd and Cu in over-ground part and underground part after lettuce is planted for a quarter, to investigate the passivation effect of charcoal application treatment on Cd and Cu pollution in soil. The main conclusions are as follows: (1) The pore volume of the mesoporous of the wood charcoal used for test is0.2700cm3·g-1; the pore volume of macropore and micropore are separately0.0035cm3·g-1and0.0398cm3·g-1;specific surface area is27.5808m2·g-1; organic carbon content is8.1929g2·kg-1; pH value is7.91; it is observed under electron microscopy that charcoal surface is characterized by obvious porosity, which shows that the charcoal’s specific surface area is very large and interface energy is high.(2) The isothermal adsorption of the tested wheat straw charcoal, peanut shell charcoal and wood charcoal for Cd2+conforms to Langmuir Equation, with the maximum adsorbing capacity respectively being0.673,0.134and0.068mg·g-1, while the isothermal adsorption of wheat straw charcoal, peanut shell charcoal and activated charcoal for Cu2+conforms to Freundlich Equation; the adsorption of wheat straw charcoal, peanut shell charcoal and wood charcoal for Cd2+can achieve a balance within60rnin. When the dosage of biochar is2g·L-1and the initial pH of the solution is6, the adsorption of wheat straw charcoal, peanut shell charcoal and wood charcoal for Cd2+can achieve the optimal effect, and the absorption effect of wheat straw charcoal on Cd2+is obviously superior to that of peanut shell charcoal and wood charcoal for Cd2+, with the removal rate able to reach91.3%; the adsorption of wheat straw charcoal, peanut shell charcoal and activated charcoal for Cu2+can achieve a balance beyond10h; when the dosage of biochar is8g·L-1and the initial pH of the solution is6, wheat straw charcoal and peanut shell charcoal can remove96.12%and92.10%of Cu2+.(3) In pot experimental conditions, different dosages of wood charcoal has different impacts on the accumulation of pakchoi dry substance, and when the dosage of wood charcoal is greater than50g·kg-1, the accumulation of pakchoi dry substance can be improved effectively; in single pollution and combined pollution of Cd and Cu, the nitrate content in pakchoi increases with the dosage of wood charcoal, and the increasing trend becomes more and more obvious as time goes on; in single pollution of Cd and Cu, adding wood charcoal can reduce the content of Cd and Cu in pakchoi, and the content of Cd in roots decreases with the increasing of the dosage of wood charcoal; in combined pollution of Cd-Cu, adding wood charcoal has few impacts on the content of Cd and Cu in pakchoi; after wood charcoal is added, the pH value of the soil attacked by single pollution increases gradually as time goes on, and a larger dosage of wood charcoal leads to a higher pH value; when the dosage of wood charcoal is50g·kg-1, the total content of Cd and Cu and the content of effective state in soil can be controlled effectively. After wood charcoal is added for180-270d, the total content of Cd and Cu the content of effective state in soil can reach the relative minimum value, and270d later, the total content of Cd and Cu the content of effective state in soil will begin to increase again.(4) Field experimental results indicate that after wood charcoal is applied for60d, the content of acid exchangeable cadmium is reduced by6.58%～17.34%, and the content of acid exchangeable cadmium is largely unchanged if wood charcoal isn’t applied; treated in different ways, the content Fe-Mn oxides bound Cd is reduced by38.18%-53.40%, the content of organic-bound Cd is reduced by17.33%～67.24%, and the content of residual Cd is reduced by20.00%～57.60%; in case90kg of wood charcoal is applied for a Chinese acre,60d later, the content of organic-bound Cu rises by49.11%; within300d after60kg and90kg of wood charcoal is respectively applied for a Chinese acre, the content of residual Cu will separately rise by1.31%and9.80%.To sum up, in water absorption test, among the biochars for test, wheat straw charcoal has the best absorption and fixation effect. When pH is equal to6, and the dosage of wheat straw charcoal is separately2g·L-1and8g·L-1, it can remove96.12%and91.30%of Cd2+and Cu2+; in pot cultural conditions, when the dosage of wood charcoal is50g·kg-1, the total content of Cd and Cu and the content of effective state in soil can reach the relative minimum value between90d and120d; in field experiment, after60kg of biochar is applied for a Chinese acre, the content of acid exchangeable Cd is reduced by over5%, after30kg or90kg of biochar is applied for a Chinese acre, the content acid exchangeable Cd is reduced by over15%, and after90kg of biochar is applied for a Chinese acre, the content of organic-bound Cu in soil will rise by49.11%60d later, thus reducing the available-form ratio of soil heavy metals. Therefore, it’s feasible to abate and remedy the heavy metal pollution in water and soil environment with the use of biochar.