Effect of Rice Husk Biochar on Cadmium Immobilization in Soil and Uptake by Wheat Plant Grown on Lacustrine Soil

摘要

Production of biochar from crop residues using pyrolysis technology is considered one of the recent technologies to use the pyrolized residues as recalcitrant adsorbent materials to remove heavy metals from wastewater and immobilize metalic contaminants in soils. Rice husk biochar (RHB) was produced by pyrolysis of rice husk (RH) at 450 degC for 15 min. in the laboratory. Surface area, pore volume and FTIR techniques were used to characterize both RH and RHB. Adsorption isotherm experiments were carried out to measure the adsorption of Cd~(2+) (875 mg Cd2+ kg"1) on RH and RHB for 96h. Greenhouse experiment was conducted to investigate the effect of biochar application (by rate of 30t ha~(-1)) to soil in presence of Cd~(2+) (0, 5 and 35 mg kg~(-1) soil) on the yield and Cd~(2+) uptake by wheat plants. Produced biochar had higher surface area and total pore volume by about 10 and 2.73 times, respectively, than the feedstock (RH). Adsorption Isotherm showed that about 97.3 and 63.2% of Cd~(2+) were removed within the first 2 h of reaction by RHB and RH, respectively. There was increase in pH values only associated to RH adsorption of Cd~(2+) which reflects an increase in electronegativity or changing in the status of surface functional groups of RH.The high values of adsorption and stable pH values during Cd~(2+) adsorption on RHB reveals the stability of active surfaces and surface groups of biochar with time. There was a significant increase in concentrations of DOC with reaction time only in RHtreatment and it was not observed in RHB treatment. DOC results pointed out the potentiality of degrading and decaying the RH adsorption system with time, and reflects the recalcitrant feature of RHB system. The Results of greenhouse showed a significantreduction in grain and straw yield and high rates of Cd~(2+) uptake with increasing concentrations of added Cd~(2+). Application of RHB greatly reduced the hazardous effect of Cd~(2+) on the growth and yield and significantly diminished the accumulationof Cd~(2+) in both wheat grain and straw.