地质聚合物-生物炭复合材料的制备及对Pb2+的吸附性能和机制

Preparation of geopolymer-biochar composite and the adsorption properties and mechanism for Pb2+

摘要:

为提高单一类型吸附剂（地质聚合物或生物炭）吸附量，以矿渣、玉米秸秆生物炭为原料，氢氧化钠为激发剂，制备地质聚合物-生物炭复合材料G3.0BC10，通过水溶液吸附实验测试其对Pb2+的吸附性能，考察溶液pH值、G3.0BC10投加量对其Pb2+吸附性能的影响，以及金属离子（Cu2+、Zn2+）和有机物（苯酚）对其Pb2+吸附性能的影响，探究G3.0BC10对Pb2+吸附的动力学、等温线和循环使用性能，基于XRD、SEM、FTIR、BET表征，推测G3.0BC10对Pb2+的吸附机制。结果表明，硅铝比为3.0、玉米秸秆生物炭加入质量为矿渣总质量的10%制备的G3.0BC10比表面积（55.6 m2/g）较无玉米秸秆生物炭掺杂制备的G3.0（15.5 m2/g）增加了258.7%，羟基、羧基等官能团数量明显增多；当溶液pH＝5~7，G3.0BC10加投量为1 g时，其对100 mL质量浓度500 mg/L的硝酸铅的Pb2+去除率达到99%以上；G3.0BC10对Pb2+的吸附是以物理吸附为主的单分子层吸附过程，更符合拟二级动力学模型（R2＝0.9354）和Langmuir等温吸附模型，最大理论吸附量为1274.217 mg/g；金属离子（Cu2+、Zn2+）的存在会降低G3.0BC10对Pb2+吸附量4.61%，有机物（苯酚）的存在会稍微提高G3.0BC10对Pb2+吸附量0.16%，经历6次循环使用，G3.0BC10对Pb2+去除率从99.5%降至80%；G3.0BC10对Pb2+的吸附机制包括络合作用、离子交换作用、结构吸附作用，生物炭的添加改善了地质聚合物的孔隙结构，增大其比表面积，并提供了丰富的含氧官能团。

Abstract:

In order to improve the adsorption capacity of a single type of adsorbent (geopolymer or biochar), a geopolymer-biochar composite material G3.0BC10 was prepared by using slag and corn straw biochar as raw materials and sodium hydroxide as an activator. The adsorption performance of G3.0BC10 on Pb2+ was tested by aqueous solution adsorption experiments. The effects of solution pH value and G3.0BC10 dosage on its Pb2+ adsorption performance, as well as the effects of metal ions (Cu2+, Zn2+) and organic matter (phenol) on its Pb2+ adsorption performance were investigated. The kinetics, isotherm and recycling performance of G3.0BC10 for Pb2+ adsorption were explored. Based on XRD, SEM, FTIR and BET characterization, the adsorption mechanism of Pb2+ by G3.0BC10 was speculated. The results showed that the specific surface area (55.6m2/g) of G3.0BC10 prepared with a silicon-aluminum ratio of 3.0 and a corn straw biochar addition of 10 % of the total mass of the slag was 258.7 % higher than that of G3.0 (15.5m2/ g) prepared without corn straw biochar. The number of functional groups such as hydroxyl and carboxyl groups increased significantly.When the pH of the solution was 5~7 and the dosage of G3.0BC10 was 1 g, the Pb2+ removal rate of 100 mL lead nitrate with mass concentration of 500 mg/L reached more than 99 %. The adsorption of Pb2+ by G3.0BC10 was a monolayer adsorption process dominated by physical adsorption, which was more in line with the pseudo-second-order kinetic model (R2=0.9354) and Langmuir isotherm adsorption model. The maximum theoretical adsorption capacity was 1274.217 mg/g ; the presence of metal ions (Cu2+, Zn2+) will reduce the adsorption capacity of G3.0BC10 for Pb2+ by 4.61 %, and the presence of organic matter (phenol) will slightly increase the adsorption capacity of G3.0BC10 for Pb2+ by 0.16 %. After 6 cycles, the removal rate of Pb2+ by G3.0BC10 decreased from 99.5 % to 80 %. The adsorption mechanism of Pb2+ by G3.0BC10 includes complexation, ion exchange and structural adsorption. The addition of biochar improves the pore structure of geopolymer, increases its specific surface area and provides abundant oxygen-containing functional groups.