Experimental Study On The Remediation Of Simulative Cadmium Contaminated Soils By Activated Bochar

Heavy metal pollution in soil not only makes the degradation of soil fertility, but alsoreduces the yield of agricultural products. It will ultimately get into human body through thefood chain and endangers human health. Looking for a low-cost and effective soilremediation technology has become a research hotspot in recent years to alleviate theaggravating of heavy metal pollution of the soil. Biochar is a suitable material to achieve thisgoal because of its developed porous structure, large specific surface area, high stab ility andgood adsorption property. In this study, the physicochemical properties of biochar made frombiomass gasification were improved by activation. Then the activated biochar was used toadsorb cadmium in solution and contaminated soil. The effect of soil remediation wasevaluated by soil culture and leaching experiments. The main research contents and resultsare as follows:(1) The physicochemical properties of biochar were studied after HNO3and steamactivation. Compared with the raw biochar, the ash content was reduced by76.5%and22.8%with HNO3and steam activation, while the cation exchange capacity(CEC) wasincreased by23.37%and32.19%, respectively. The content of acidic oxygen functionalgroups on surface was increased by51%after HNO3activation. The specific surface areawas also increased by197%after high temperature steam activation.(2) The adsorption capacities of Cd on raw and activated biochar were investigated withkinetics adsorption experiments and isothermal adsorption experiments. The adsorptioncapacities increased after activation and increased with adsorption temperature. Theadsorption isotherms of the three kinds of biochar were described by pseudo-first-orderkinetic equation and Langmuir model.(3)The influences of water content, pH value and incubation time on the bioavailablecadmium content and the existing forms of cadmium in the cadmium contaminated soilswith additional biochar were investigated. The content of bioavailable cadmium decreasedwith the increasing of water content, pH value and incubation time. The content ofbioavailable cadmium decreased69.2%、61.68%、56.57%in the soils with steam activatedbiochar, HNO3activated biochar and raw biochar at the highest water content. While the results were85.69%、82.91%、78.32%at the highest pH value and69.23%、64.51%、57.69%at the longest incubation time. With the increasing of water content, pH value and incubationtime, the flexible forms of cadmium including water-soluble cadmium and exchangeablecadmium were transformed into Fe-Mn oxides bounded cadmium, organic matter boundedcadmium and residual cadmium, which were very stable and low bioavailable.(4)The results of leaching experiments indicated that the release of cadmium in the soilswith additional biochar decreased. Compared with the soil before remediation, the releaseamount of cadmium in the soils with steam activated biochar, HNO3activated biochar andraw biochar decreased by54.33%,50.63%and38.40%, respectively.