Immobilization Of Pb²⁺ And Cd²⁺ In Contaminated Waters And Soils By Biohcars Derived From Meat And Bone Meal

Lead (Pb) and cadmium (Cd) are typical heavy metal pollutants with strong cumulative ability in water and soil. Pb and Cd can be absorbed by human body through the food chain and then threaten the health of human beings. Biochars derived from animal residues contain large amounts of calcium phosphate which are known to form stable minerals and complexes with heavy metals. Biochars produced from meat and bone meal waste materials are potentially useful sorbents for the remediation of metals. In this study, biochars from pig carcasses (Meat and bone biochar, MB) and biochars from corn stalk(Corn stalk biochar, CS) were prepared at 600℃ by oxygen-limited pyrolysis, and the physical and chemical properties of biochars were studied. Batch experiments were used to study the adsorption characteristic of Pb2+ and Cd2+ by the MB biochars. Besides, the effects of MB biochar remediation on soil environmental quality and the Pb/Cd content in soil were studied by laboratory simulation. The main results are as follows:(1) There are many significant differences on the physical and chemical properties between MB and CS. The ash content of MB is 67.16%, which is about 2 times the ash content of CS; the content of carbon, hydrogen, nitrogen in MB is 25.73%,1.00% and 2.42%, respectively; the specific surface area, pore volume and average pore diameter of MB are less than CS.(2) Comparing with the CS biochar, the MB biochar has much higher adsorption capacity and faster adsorption rate for Pb2+ and Cd2+. The sorption process for Pb2+ and Cd2+ on MB biochar is reached equilibrium state at 240 and 90 minites. The saturated adsorption capacities for Pb2+ and Cd2+ on MB are 106.4 and 49.57 mg/g, which are 1.5 and 1.4 times the adsorption capacities on CS. The adsorption process could be well fitted by pseudo-second order model, and Langmuir equation could better imitate the isothermal process of biochar to Pb2+ and Cd2+(3) Results showed that the addition of biochars can improve soil pH value, cation exchange capacity and organic matter content. The promotion effect of MB is much more obvious than CS. The soil pH value, cation exchange capacity and organic matter content increased 0.49～1.07,2.26～5.41 cmol/kg and 1.03-6.30 g/kg, respectively. In contaminated soil, biochars can reduced acid extractable form concentrations of Pb and Cd, thus lessen bioavailability of heavy metal.Adsorption rate and adsorption capability of Pb on MB biochar were all larger than that on CS biochar. Compared with CK, the Pb, Cd content of accumulated leachates decreased, and the treatment of MB had the better effect on reducing leaching amount of Pb, Cd from soils.In conclusion, biochars derived from meat and bone meal can adsorb heavy metals in the solution, improve soil physical and chemical properties, and reduces the biovailability of heavy metals in the contaminated soil.