V^(5+)和V^(4+)在不同生物炭柱中淋溶特性及其影响因素研究

V^(5+)and V^(4+)Leaching in Different Biochar Columns and Influencing Factors

生物炭对重金属离子有良好滞留作用,被广泛用作吸附剂来去除地表径流及地下水中的重金属。选用粒径为0.80 mm的木炭和竹炭,通过柱淋溶试验探究V^(5+)和V^(4+)在两种生物炭柱中的淋溶特性,并分别研究钒价态、初始钒浓度、溶液pH以及有机酸种类和浓度等因素对钒迁移的影响。结果表明,木炭和竹炭颗粒对V^(5+)吸附较弱,而对V^(4+)吸附较强。当淋溶液体积为3 PV(PV为孔隙体积,60 mL)时,不同初始浓度V^(5+)出流比(出流液与注入液浓度的比值)在两种生物炭柱中均达到0.90以上,表明V^(5+)迁移性强,初始浓度对生物炭吸附V^(5+)影响不显著。当淋溶液体积为8 PV时,初始质量浓度为5 mg·L^(-1)的V^(4+)溶液出流比约为0.90,而40 mg·L^(-1)的V^(4+)溶液出流比降低到0.63以下,表明随着初始V^(4+)浓度增大,生物炭对V^(4+)的吸附量显著增加。随着淋溶液pH升高,两种生物炭对V^(5+)和V^(4+)的吸附量降低,进而V^(5+)和V^(4+)溶液出流比增大,pH为5.5时V^(5+)和V^(4+)溶液出流比在木炭柱中分别为0.88和0.58,在竹炭柱中分别为0.83和0.53。当淋溶液中加入不同浓度草酸和柠檬酸时,高浓度有机酸能促进V^(5+)淋溶,低浓度则会抑制淋溶。与草酸相比,柠檬酸对V^(5+)在两种生物炭柱中淋溶的抑制效果更明显。傅里叶红外光谱(FTIR)分析结果显示,生物炭表面主要为酸性含氧官能团,如羧基、羰基和羟基等,易与V^(5+)和V^(4+)络合沉淀。当溶液pH降低,生物炭表面酸性含氧官能团数量增加,从而显著促进生物炭对V^(5+)和V^(4+)的吸附固定作用。

Biochar has a great retention potential on metal ions and has been widely used to remove heavy metals from surface runoff and groundwater.In this study,wood charcoal and bamboo charcoal with particle size of 0.80 mm were used,and the column experiments were conducted to investigate V^(5+)and V^(4+)leaching in the two types of biochar columns.The effects of vanadium valence state,initial vanadium concentration,solution pH,types and concentrations of organic acids on vanadium migration were studied.The results indicate that the retention efficiency of V^(5+)in the wood charcoal and bamboo charcoal columns was low,while the retention efficiency of V^(4+)was high in both types of columns.When the injection amount was three times of PV(pore volume,60 mL),the effluent ratios(the ratio of effluent concentration to inlet concentration)of different initial V^(5+)concentrations exceeded 0.90 in both types of biochar columns,indicating that V^(5+)had a high migration rate in biochar columns and the influence of initial V^(5+)concentration on retention was not significant.When the injection amount was 8 times of PV,the effluent ratio for the V^(4+)solution with an initial concentration of 5 mg·L^(-1)was about 0.90,whereas the effluent ratio for the V^(4+)solution with an initial concentration of 40 mg·L^(-1)decreased to below 0.63.This suggests that the migration rate of V^(4+)in biochar columns had significantly decreased with the initial V^(4+)concentration increased.With the increase in leachate pH,the retention rates of V^(5+)and V^(4+)in both types of charcoal columns decreased,subsequently leading to an increase in the effluent ratios of V^(5+)and V^(4+)solutions.At the leachate pH of 5.5,the maximum effluent ratios for V^(5+)and V^(4+)in the wood charcoal column were 0.88 and 0.58,respectively,while they were 0.83 and 0.53 in the bamboo charcoal column.When different concentrations of oxalic acid and citric acid were added into the leachate,it was observed that high concentration organic acid promoted V^(5+)leaching,whereas low concentration organic acid inhibited V^(5+)leaching.Compared to oxalic acid,citric acid had exhibited stronger effect in inhibiting V^(5+)leaching in both the two types of biochar columns.Fourier-transform infrared spectroscopy(FTIR)analysis had revealed that the surfaces of biochar were predominantly characterized by acidic oxygen-containing functional groups,such as carboxyl groups,carbonyl groups,hydroxyl groups,and other functional groups,which readily formed the complexes and facilitated the deposition of V^(5+)and V^(4+).Under the condition of low pH value of the solution,the content of these acidic oxygen-containing functional groups on the biochar surface had increased,thereby significantly promoting the adsorption of V^(5+)and V^(4+)on biochar.