壳聚糖螯合铬(Ⅵ)的稳定常数测定及螯合效果分析

Determination of Stability Constant and Analysis of Chelating Effect of Chitosan Chelating Chromium (Ⅵ)

为了考察壳聚糖(CTS)对重金属离子铬(Ⅵ)的螯合性能,利用紫外分光光度法对壳聚糖螯合铬(Ⅵ)的机理进行了研究,测定了不同c(Cr^6+)/c(-NH+3)浓度比下壳聚糖-铬(Ⅵ)螯合物的紫外吸收光谱,确定了螯合物的配位比并计算了稳定常数。结果表明:壳聚糖对铬(Ⅵ)具有螯合作用,在不同壳聚糖氨根配体浓度下,当c(Cr^6+)/c(-NH+3)≥0.5时,螯合反应达到平衡;壳聚糖中主要配体-NH 2基团与铬(Ⅵ)按物质的量比2∶1形成螯合物,壳聚糖铬(Ⅵ)螯合物的稳定常数为1.212×10^8。通过实验考察了壳聚糖用量、体系pH对壳聚糖螯合铬(Ⅵ)离子效果的影响。结果表明:壳聚糖用量为0.15 g·L,反应酸碱度为pH=4的弱酸环境时,铬(Ⅵ)离子去除率可达到87.5%。

To investigate the chelation properties of chitosan to heavy metal ions Cr(Ⅵ), the mechanism of chelating Cr(Ⅵ) with chitosan was studied in ultraviolet spectrophotometry. The ultraviolet absorption spectra of chitosan-Cr(Ⅵ) chelate at different c(Cr6+)/c(-NH+3) concentration ratios were measured, on which the coordination ratio of the chelate was determined and its stability constant was calculated. The results show that chitosan had chelating ability to Cr(Ⅵ). At different chitosan ammonia ligand concentration, when c(Cr6+)/c(-NH+3) was above 0.5, the chelating reaction reached equilibrium. The main ligand in chitosan-NH2 group formed a chelate with Cr(Ⅵ) according to the molar ratio of 2∶1, and the stability constant of chitosan Cr(Ⅵ) chelate was 1.212×108. The effects of the chitosan dosage and pH value on the chelating effect of chitosan on Cr(Ⅵ) ions were investigated experimentally. The results show that the removal rate of chromium ions an reach 87.5% when chitosan dosage is 0.15 g/L at pH=4.