不同类型粘土矿物对镉吸附与解吸行为的研究

Study on cadmium adsorption-desorption behavior of diffrent clay minerals

[目的]揭示镉在土壤环境中的化学行为。[方法]采用批量吸附试验研究了4种不同类型的粘土矿物:蒙脱石、高岭石、针铁矿、三水铝石对镉的吸附与解吸特性,同时探讨了矿物用量及pH对镉吸附的影响。[结果]与Freundlich方程相比,Langmuir方程(R2>0.98)能较好的表征4种矿物对镉的吸附行为,说明矿物对镉的吸附是单层吸附。4种矿物对镉的最大吸附量大小为:蒙脱石(32.62mg·g-1)>针铁矿(11.52mg·g-1)>高岭石(7.99mg·g-1)>三水铝石(6.29mg·g-1)。4种矿物对镉的解吸率范围分别为:蒙脱石(19.99%~32.77%)、高岭石(13.48%~19.09%)、针铁矿(2.02%~3.48%)、三水铝石(1.09%~2.43%)。随pH升高蒙脱石、高岭石、针铁矿对镉的吸附量均呈增长趋势,而三水铝石基本保持不变。矿物用量在10.0g·L-1时,针铁矿对镉的吸附率达72.8%,与蒙脱石相近(79.1%)。[结论]针铁矿吸附率较高,而解吸率低,是一种较好的吸附剂。

[Objective]To study on cadmium chemical behavior in soils. [Methods] A batch adsorption experiment was used to investigate the adsorption-desorption of Cd（ Ⅱ ） on four clay minerals, such as kaolinite, montmorillonite,goe- thite and gibbsite. [Results]And the quantity of the added clay mineral and the impact of solution with various pH val- ues on the adsorption of Cd（ Ⅱ ） on the four target mineral clays was investigated. The results showed that Langmuir equation was more accurately than the Freundlich equation in describing adsorption behavior of cadmium the sequence of the adsorption amounts of four clay minerals： montmorillonite （32.62 mg. g- 1 ） 〉goethite（ 11.52 mg. g- 1 ）〉 kaolinite （7.99 mgg-1）〉gibbsite（6. 29 mg,g-1 ）. The range of cadmium desorption rate of montmorillonite, kaolinite, Goe- thite and gibbsite were 19.99%-32.77%,13.48%-19.09%, 2.02%-3.48%, 1.09%-2.43%, the adsorption amounts of Cd（Ⅱ ） on the four clay minerals was increased with the rising of pH values. But gibbsite basically remain unchanged. When the amounts of the added clay mineral was 10.0 g. L-1 , the cadmium adsorption rate of goethite is 72.8% ,and it is close to montmorillonite. [Conclusion]Compaired with montmorillonite, kaolinite and gibbsite, goe- thite had relatively high, adsorption amounts, and low desorption rate, so it was a better adsorbent.