Application Of Different Biochar Modified By Chitosan In Soil Improvement And Remediation Of Heavy Metal Pollution

In Hainan’s humid climatic conditions,rainfall makes the soil have a strong leaching effect,resulting in soil acidification and fertility decline.At the same time,the toxicity of heavy metals will increase with soil acidification,increasing the potential toxicity risk of heavy metals to crop accumulation.Due to its unique physical and chemical properties,biochar can effectively improve the ability of soil to hold water and fertilizer and passivate heavy metals in the soil,but the easy saturation of the original biochar is the limitation of its further application.In this study,rice husk biochar（BR）,corn cob biochar（BC）,bagasse biochar（BS）and banana pseudostem biochar（BB）were prepared from typical agricultural wastes in Hainan,and the biochar was modified by introducing chitosan（Chitosan,C）.The feasibility of chitosan-modified biochar in fixing soil nutrients and passivating heavy metals lead and cadmium was explored by using acid soil improvement test and heavy metal contaminated soil passivation test,in order to develop new environmentally friendly materials with high performance and low cost.After experimental research,the main conclusions are as follows:（1）The characterization test results show that the physical and chemical properties of biochar are closely related to the properties of raw materials.All four biochars are alkaline（p H>7）,and the loading of chitosan increases the alkalinity and conductivity of biochar.After chitosan modification,the specific surface area of the four biochars decreased to varying degrees,and the pore size increased,showing lower C and higher O content,while the characteristic peaks of-NH₂ and-OH at 3400 cm^-1 and 1600 cm^-1were enhanced.（2）The results of acid soil improvement test showed that the p H,EC,effective nutrients（N,P,K）,Cation exchange capacity,organic matter and enzyme activity content of acidic soil were increased by the four biochar and chitosan-modified biochar,and there were obvious differences between different treatments.For soil P,K,CEC and organic matter,the improvement effect of unmodified biochar was better.For soil p H,EC,N,sucrase,urease,chitosan-modified biochar improvement effect is better.（3）The results of heavy metal contaminated soil remediation test show that different treatments can Pb and Cd in soil,reduce the contents of water-soluble,carbonate-bind,iron-manganese-bound and organic bonded,and increase the content of residual state,and the heavy metal passivation effect and brassica chinensis growth of chitosan-modified biochar are better than those of unmodified biochar.