负载金属捕获剂改性PAC吸附低温水中低浓度Cr(Ⅵ)特性

摘要

针对低温微污染水中(275 K)低浓度Cr(Ⅵ)离子(0.500 mg·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. 500 mg · L-1) on the TA-PAC was investigated at various dosage and pH, and adsorption capacities and adsorption isotherms were measured at 275 K. 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. 010 to 0. 404 mg · L-1 , R2 = 0. 9941, indicating a heterogeneous coverage of chromium on TA-PAC. 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.