Immobilization Of Pb And Cd Pollution In The Environment By Sludge Biochars

In recent years, with the increasing of sludge yield, how to make good use of the intrinsic value of the sludge and change waste to treasure is a hotspot of current research. Pyrolysis can effectively degrade and stabilize the toxic and harmful components in sludge, which is a kind of sludge disposal method at present. Biochars is a fine granular charcoal, produced by the plant or waste materials in the anoxic environment. Biochars contain a large number of aromatic ring structure carbon, with a larger porosity, surface with negative charge and containing a large number of functional groups, which can adsorb and fix heavy metals in the environment, and can improve soil structure, promote crop growth. In this experiment, sludge-derived biochars were prepared at different pyrolysis temperature (300,400,500℃) using Yangzhou municipal sewage sludge as raw materials, to study the adsorption characteristics of Cd2+and Pb2+in aqueous solution with different pyrolysis temperature, and to investigate the effects of the adsorption time, pH and the equilibrium concentration of the solution on the adsorption, combined with EDS, SEM and FTIR, mechanism of its action and discussing the potential value of sludge biochars as adsorbent for treating heavy metal polluted wastewater. Further research on Pb and Cd chemical forms change and the biomass and the accumulation of heavy metals in small vegetables in contaminated soil is added the sludge biochar, combined with the characteristics of biochar, analyzed the Pb and Cd chemical forms with the time varying law, to reveal the mechanism of sludge biochar on soil improvement, in order to provide theoretical support for the remediation of contaminated soil. The main conclusions are as follows:(1) Pseudo-second-order kinetic model can effectively describe the process of the adsorption of Pb2+and Cd2+by sludge-derived biochars almost reached in 30hours, which was mainly controlled by chemical reaction. As the solution pHs increased, the amount of Pb2+and Cd2+ absorbed by the sludge-derived biochars gradually increased then decreased. The maximum adsorption amount of Pb2+appeared at pH 4.5, while that of Cd2+at pH 6.5. Theamount of Pb2+and Cd2+absorbed by sludge-derived biochars is RC500>RC400>RC300 at 25℃, and to Pb2+the adsorption capacity of RC500 is 14.39 mg·g-1 more than the adsorption of Cd2+(1.45 mg·g-1).(2) In the soil contaminated by Pb and Cd added the sludge biochar, the pH increased significantly with the increase of the balance time. Whether in a single or in a composite pollution, sludge biochar has good fixation effect on Pb and Cd in the contaminated soil, And the fixed effect of Pb is better than Cd. At the same time, the fixed effect of Pb in composite pollution is better than that in single, and Cd fixed effect is the opposite.(3) The biomass of the small vegetables could be improved by the addition of sludge biochar, and the contents of Pb and Cd were significantly lower. In a single contaminated soil, the Pb content of the small vegetables reached 4.56%, and the Cd reached 14.79%. However in the composite pollution soil, the Pb content of the small vegetables reached 31.67%, and the Cd reached 8.67%.