玉米皮渣制备生物炭吸附含Cr(Ⅵ)废水研究

Study on Cr(Ⅵ) Removal by Corn-bran Residue and its Bio-chars

采用玉米皮渣为原料,在300、400、500和600℃炭化温度下制备生物炭。考察温度对生物炭特性影响,研究了溶液p H、初始Cr(Ⅵ)浓度和生物炭使用量对Cr(Ⅵ)除去率影响。随着炭化温度升高,生物炭收率降低。生物炭红外光谱显示,生物炭富含羧基、酚羟基等表面含氧官能团,低温生物炭还含有饱和的烃基和长链烃基。随温度升高,生物炭中脂肪性烷基链消失,而芳香性逐渐增加。玉米皮渣及其生物炭在Cr(Ⅵ)溶液p H为1~2时对Cr(Ⅵ)除去效果最好,这说明p H会影响Cr(Ⅵ)在水溶液中的离子形态,并对吸附剂的稳定性与化学官能团活性产生影响。Cr(Ⅵ)初始浓度为50~500 mg/L时,玉米皮渣和生物炭对Cr(Ⅵ)的吸附能力范围为8.2~86.5mg/g。与生物炭相比,玉米皮渣富含还原性基团如SO_3^(2-),对Cr(Ⅵ)去除率达到96%。Freundlich、Langmuir和Dubinin-Raduskevich模型拟合结果说明,玉米皮渣和生物炭对Cr(Ⅵ)除去能力还与吸附剂特性相关,且去除机理以物理吸附与还原作用为主。

Bio-chars were produced from corn-bran residue （ CBR） at temperatures range from 300 to 600°C. The CBR and CBR-derived bio-chars were characterized and utilized to remove Cr（Ⅳ） from aqueous solutions. CBR-chars were produced at high temperatures have larger specific surface area and lower content of functional groups. The Cr（Ⅳ） removals by CBR and bio-chars were mainly obtained by the reduction from Cr（Ⅳ） to Cr （Ⅲ） through SO2-3 or oxygen-containing functional groups from these adsorbents. The amount of Cr（Ⅳ） removed by the adsorbents ranged from 8.2 to 86.5 mg/g at the initial Cr （Ⅳ） concentrations of 50~500 mg/L. The SO2-3 -rich CBR was showed to be more effective and economical for Cr（Ⅳ） removal than others,which has the Cr（Ⅳ） removal efficiency of 96%. The data could also be modeled by Freundlich,Langmuir and Dubinin-Raduskevich isotherms,suggesting that the Cr（Ⅳ） adsorption process was complex and related with adsorbent properties and solution pH. The results also indicated that the Cr （Ⅳ） adsorptions by CBR and CBR-derived biochars were reduction coupled with physical adsorption.