Study On The Change Of Soil Cadmium,Lead And Zinc Speciation By Different Biochar In The Area Of Native Zinc Smelting In Northwest Guizhou Province

With the rapid development of China's economy,a large number of heavy metal pollutants are discharged into the soil environment through human activities,resulting in serious soil heavy metal pollution.Biochar,as friendly environment passivated material,has complex pore structure,huge specific surface area and abundant functional groups,and has strong adsorption and fixation effect on heavy metals pollutants.In recent years,biochar has become a research hotspot in the environment field.The properties of biochar prepared from different raw materials vary greatly,there are few studies on biochar passivation with different particle sizes for remediation of heavy metal contaminated soil at present,the biochar of different types as passivation materials,the Hezhang county in Guizhou province Bijie city indigenous zinc smelting area of Cd,Pb,and zinc contaminated soil as the research object in this study.The corn straw and rice husk biochar were prepared at 300,400 and 500?respectively,denoting C(300),C(400),C(500),W(300),W(400)and W(500),respectively.The modified biochar was denoted as CG(300),CG(400),CG(500),WG(300),WG(400)and WG(500)respectively.The particle size of biochar was divided into 1:small particles(0.075-0.2 mm),2:medium particles(0.2-0.45 mm)and 3:Large particles(0.45-1 mm)in 3 grades,cross combination.The morphology,organic element content,mineral composition and functional groups of biochar were characterized by Fourier transform infrared spectroscopy(FTIR)and other technical means,and the change characteristics of physicochemical properties of biochar and soil were analyzed.To explore the mechanism and effect of biochar on the effective,toxic leachate and chemical forms(weak acid extraction,reducible,oxidizable and residue)of Cd,Pb and Zn in soil.In order to provide basic experimental data and pollution prevention and control ideas for passivation repair of heavy metal contaminated soil by biochar.The main results are as follows:(1)The biochar mainly contains C and O elements,and the content of C and O elements increases with the increase of pyrolysis temperature,and less aromatic.The aromatic degree and polarity of corn straw biochar gradually increase with the increase of pyrolysis temperature,while the aromatic degree of rice husk biochar increases with the increase of temperature,and the aromatic degree and polarity of rice husk biochar increase with the increase of temperature,and the aromatic degree and polarity of rice husk biochar increase first and then decrease.The functional groups were mainly-OH,C-H,C-O,C=O,C=C and C-O-C in the biochar.The pore structure of biochar is obvious,and has granular substance on its surface.The specific surface area and total pore volume of rice husk biochar were significantly higher than the corn straw biochar,but the average pore size was lower than that of corn straw biochar,and the specific surface area of rice husk biochar increased with increasing pyrolysis temperature.XRD analysis showed that the corn straw and rice husk biochar mainly contained Si O₂ and KCl,and the minerals mainly included quartz,feldspar,mica,zeolite,illite and chlorite in the tested soil.(2)The modified rice husk biochar(0.075-0.2 mm)had the greatest effect on p H,which increased soil p H by 0.41 units,and had a more obvious effect on EC,which increased by 288.1?m·cm^-1 in W2(500)treatment.The tested soils were poor in water and fertilizer conservation,and corn straw and rice husk biochar had different effects on CEC.The contents of SOM of corn stalk biochar were decreased,and that of rice husk biochar was similar,but WG1(400)and W2(500)treatments could increase SOM by 3.56 and 5.59 g·kg^-1,respectively.The passivation treatment could increase soil TP content.(3)The best passivation effect for effective Cd,Pb and Zn was WG2(300),W2(300)and W3(500),with the decrease of 19.93,53.52 and44.91%,respectively.It was found that rice husk biochar had better passivation effect than corn stalk biochar.For Cd,Pb and Zn,the passivation effect of rice husk biochar was better than that of corn stalk biochar,which were W2(400)and W2(300).The decrease rate can reach41.56,62.45 and 36.13%.After the treatment of the two biochar,the contents of Cd and Pb in the residue of most treatments increased,and the mobility and toxicity decreased,but the chemical form of Zn was not affected.