负载金属捕获剂改性PAC吸附低温水中低浓度Cr(Ⅵ)特性

Adsorption characteristics of metal-capture-agent immobilized PAC for low concentration Cr(Ⅵ)in water at low temperature

针对低温微污染水中(275K)低浓度Cr(Ⅵ)离子(0.500mg.L-1),制备基于表面负载食品级单宁酸为金属捕获剂的改性PAC(TA-PAC),以HNO3、NaOH氧化改性PAC为对照,研究了TA-PAC的表面物理化学特性和吸附性能,并进行了pH影响和吸附等温线拟合研究。结果表明:TA-PAC的比表面积、总孔容积和表面极性大小最佳。TA-PAC对低温水中Cr(Ⅵ)及总铬的去除效果优于N-PAC和OH-PAC。酸性范围内(pH=3.0～6.0)TA-PAC对Cr(Ⅵ)及总铬的去除率均大于碱性范围(pH=7.0～10.0)。Freundlich双参数吸附等温式对TA-HNC吸附水中低浓度总铬的吸附等温线拟合效果最好(R2=0.9941)。TA-PAC吸附低温水中低浓度Cr(Ⅵ)是一个极为复杂的过程,主要吸附机理可能包括表面还原作用、酯化/螯合作用和离子交换作用等。

As a kind of metal-capture-agent,food grade tannic-acid（TA）was immobilized on commercial powdered activated carbon（PAC）.Adsorption of low concentration Cr（Ⅵ）（0.500mg.L-1）on the TAPAC was investigated at various dosage and pH,and adsorption capacities and adsorption isotherms were measured at 275K.Compared with HNO3-and NaOH-modified PAC（N-PAC and OH-PAC）,the results obtained from the BET,Boehm’s titration and FTIR indicated that TA-PAC is of larger specific surface area,total pore volume and more abundant acid functional groups.The performance of TA-PAC,expressed by removal efficiency of Cr（Ⅵ）and total chromium,is much more excellent than N-PAC and OH-PAC.Its adsorption capacity for Cr（Ⅵ）was found to be pH-dependent,the removal efficiency both Cr（Ⅵ）and total chromium were notably higher in the acidic medium（pH=3.0—6.0）than in alkaline medium（pH=7.0—10.0）.The adsorption data for total chromium were fitted using two-parameter isotherm models and the related parameters were estimated.Freundlich model is the best for data of Ce from 0.010to 0.404mg.L-1,R2=0.9941,indicating a heterogeneous coverage of chromium on TAPAC.Langmuir（Ⅰ）,Langmuir（Ⅱ）and Temkin models didn’t fit the data well,because of occurring piecewise node at 0.149 mg.L-1,0.151 mg.L-1 and 0.163 mg.L-1 respectively.The adsorption mechanism of TA-PAC for Cr（Ⅵ）was assumed to be chemical process,such as surface reduction of Cr（Ⅵ）,esterification between chromate and catechol,and ion exchange.