用平衡吸附法研究了不同pH下,三种有机酸(乙酸、酒石酸和柠檬酸)对针铁矿和膨润土等温吸附Cd^2+、Pb^2+的影响.结果表明:在加入的Cd^2+、Pb^2+浓度分别小于0.2 mmol L^-1和4.0 mmol L^-1时,针铁矿和膨润土吸附平衡体系的pH随加入重金属浓度的增加而降低,膨润土体系的pH降低更明显.在有机酸作用下,pH对针铁矿和膨润土吸附Cd^2+、Pb^2+的影响差异显著.3<pH< 4.5时,针铁矿Cd2+的吸附率很小;4.5<pH<8时,Cd2+吸附率明显上升,并趋向饱和吸附.针铁矿Pb2+的吸附率从pH3时开始上升,pH5.5时其吸附率基本稳定于95%.三种有机酸作用下,膨润土Cd^2+的吸附率均从40%(pH3时)缓慢地上升;pH8时吸附率近90%.pH3时,加入各有机酸的膨润土Pb2+吸附率均在60%左右;pH6时,加入柠檬酸的上升至80%,其他处理均上升至95%.不同pH下,膨润土Cd^2+、Pb^2+吸附率的变幅为40%~90%,而针铁矿的为3%~90%;有机酸对促进针铁矿吸附Cd^2+和Pb^2+的影响大小顺序均为:柠檬酸>酒石酸>乙酸,其对膨润土吸附的影响差异不明显.
Effects of organic acids (acetic acid,tartaric acid and citric acid) on Cd^2+、Pb^2+ adsorption on goethite and bentonite were studied with the batch method. Results show that pH decreased with the increase in concentration of Cd^2+ and Pb^2 + in the goethite and bentonite isothermal systems when the concentration of Cd^2+、Pb^2+ was lower than 0.2 mmol L^-1 and 4.0 mmol L^- 1, respectively. The decrease of pH in bentonite system was more obvious than in goethite system. The effect of pH on Cd^2+、Pb^2+ adsorption of goethite and bentonite varied sharply with organic acids added. Cd^2+ sorption rate was small with goethite when pH was in the range from 3 to 4.5, but it went upward sharply when pH was higher (4.5 〈 pH 〈 8), and tended toward saturation at pH 8. Pb^2+ sorption rate began to increase when pH was 3 with goethite, and it leveled off to 95 % at pH 5.5. Affected by three organic acids, Cd^2+ sorption rate increased slowly from 40% at pH 3 with bentonite, and approached close to 90% at pH 8 .Pb^2+ sorption rates were around 60% in bentonite systems added with different organic acid. They increased to 80% when citric acid was added and 95% when other organic acid added. Cd^2+、Pb^2+ sorption rates varied from 40% to 90% with bentonite at different pH,but from 3% to 90% with goethite. In terms of effect of organic acids on Cd^2+、Pb^2+ adsorption of goethite, the three acids were in the order of citric acid 〉 tartaric acid 〉 acetic acid, but the effect was not clear with bentonite.