Preparation Of Different Biochars And Its Immobilization For Pb,Cr In Contaminated Water And Soil

In recent years,due to the rapid development of industrialization,wastewater containing heavy metals was discharged into water and soil,causing serious pollution to the environment.Environmental remediation materials,as adsorbents and soil amendments,are widely used in the treatment of heavy metals.Biochar is a carbonaceous material,which is characterized with high surface area,many pores structure and abundant functional groups.It can affect the distribution,migration and bioavailability of heavy metals in the environment.As a large agricultural country,China has discharged a large number of agricultural wastes into the environment every year,resulting in waste of biomass resources and increasing environmental pollution.Biomass resources,like rice bran and camellia shell,were used to produce biochars by pyrolysis and hydrothermal carbonization,realizing the recycling utilization of waste.The physical and chemical properties of biochars were characterized by scanning electron microscopy(SEM),X-ray diffraction(XRD)and Brunauer-Emmett-Teller(BET).We studied the adsorption effect of different biochar on heavy metal Pb.At the same time,a modified biochar was prepared by precipitating ?-FeOOH onto KOH activated biochar.The influence of pH values,dosage and other factors on Cr(VI)removal was investigated,explorating the adsorption-reduction mechanism.The main research content and results are as follows:(1)Hydrothermal carbon used pure rice bran as a material was synthesized.The hydrothermal carbon was used as an adsorbent to remove Pb2+ from aqueous solution.The influence of pH values,contact time and initial Pb2+ concentration on Pb2+ removal was investigated.And hydrothermal carbon was added to Pb contaminated to observe heavy metals formation in soil.The result showed that hydrothermal carbon had porous structure and contained a large amount of oxygen-containing functional groups;it had high adsorption ability to remove Pb2+ from aqueous solution.The efficient removal occurred at pH 5 and reached equilibrium within 24 hours.When using 0.75 g·L-1 hydrothermal carbon to adsorb Pb2+ from aqueous solution that the initial concentration of Pb2+was 80 mg·L-1,adsorption quantity can reach 72.44 mg·g-1.Adding hydrothermal carbon to Pb-contaminated soil,the content of weak acid extractable Pb reduced,while the residual fraction Pb significantly increased when compared with control group,this shows that Pb transform to a more stable state.(2)Two raw materials,including rice bran and camellia shell,were used to produce biochars by pyrolysis at 650 ?.The effects of particle size,mineral composition,contact time and initial Pb2+ concentration on Pb2+ adsorption by biochars were examined.The results showed that compared to rice bran derived biochar,camellia derived biochar had smaller specific surface area,but was more effective in removing heavy metals from aqueous solutions.The adsorption isotherm of Pb2+ by camellia derived biochar fit the Langmuir model well,and the adsorption capacity is 165.62 mg·g-1 which was apparently higher than that of rice bran derived biochar(58.92 mg·g-1).The results of XRD showed that camellia derived biochar contained a large amount of mineral components and appeared precipitate after adsorption.(3)A biochar-supported nanocomposites was prepared by precipitating ?-FeOOH onto KOH activated soybean meal-derived biochars(SYBK).XRD results confirmed that ?-FeOOH was impregnated by biochars.Chromate(Cr(VI))removal capacity was investigated in a batch experiment with different conditions.The ratios of ?-FeOOH and biochars were compared for Cr(VI)removal and 20%was considered as the most efficient amount.This was possibly ascribed to highest surface area(670.65 m2·g-1)of the ?-FeOOH/SYBK nanocomposites.It was found that 20?-FeOOH/SYBK can remove as much as 96%Cr(VI)at pH 1-2 with 2 mmol·L-1 EDTA and 2 g·L-1 nanocomposites.The maximal Cr(VI)removal by 20?-FeOOH/SYBK was 37.04 g·kg-1 as estimated by Langmuir isotherm model.The removal mechanisms were examined by studying the speciation of Cr on sorbents as well as in aqueous solution.The XPS analysis of spent sorbents and chemical speciation of Cr in aqueous solutions revealed that partial Cr(VI)was reduced to Cr(III)on sorbents and in aqueous solution.This suggests the Cr(VI)can be removed by simultaneous sorption and reduction by as-prepared nanocomposites.