Abstract:

In order to investigate chelating ability of sodium carboxymethyl cellulose (CMC) on copper ions, the absorption spectra of the copper ion complex with CMC were measured via ultraviolet spectrophotometry. The composition of the complex was discussed and its stability constants were calculated. The experimental results show that CMC exhibits adsorption peak at 196 nm. When c(Cu²⁺)/c(—COO^-) is less than 0.6, the absorption peak of the complex appears at 237 nm, —COO^- group of CMC is the main ligand and reacts with Cu²⁺ in a molar ratio of 2:1 to form complex CMC-Cu²⁺, and the complex stability constant is 1.88×10¹⁰. When c(Cu²⁺)/c(—COO^-) is from 0.6 to 1.0, the maximum absorption peak of the complex appears at 214, 237 nm. —COO^- and —OH are involved in the complexation reaction to form a new complex. When c(Cu²⁺)/c(—COO^-) is greater than 1.0, the maximum absorption is in 214 nm and —OH is the primary ligand. The paper also investigates the removal effect of Cu²⁺ by CMC chelating. Experiments show that CMC-Cu directly precipitates to complexes in the solution, with precipitates as floc. c(Cu²⁺)/c(—COO^-) of 0.5 is the optimal usage of CMC in the supernatant, and the removal rate of Cu²⁺ can reach above 96%.

Key words: CMC, copper(Ⅱ), ultraviolet spectrophotometric method, chelation, stability constant

摘要：

为了考察羧甲基纤维素钠(CMC)对重金属离子 的螯合能力,利用紫外分光光度法测定了不同c(Cu²⁺)/c(—COO^-)浓度比下CMC与 形成螯合物的吸收光谱,探讨了螯合物的组成,并计算其稳定常数。结果表明:CMC对 有螯合作用,当c(Cu²⁺)/c(—COO^-)小于0.6,螯合物在237 nm处出现最大吸收峰,—COO^-为主要配体,与 按物质的量比为2:1进行螯合,此时,螯合物稳定常数为1.88×10¹⁰;c(Cu²⁺)/c(—COO^-)为0.6～1.0时,214、237 nm处出现最大吸收峰,—COO^-、—OH都参与螯合反应并形成新的螯合物;c(Cu²⁺)/ c(—COO^-)大于1.0时,214 nm存在最大吸收峰,—OH为主要配体。考察了利用CMC螯合去除溶液中 的效果,实验表明,CMC-Cu螯合物可在溶液中直接析出,析出物为絮状沉淀。当c(Cu²⁺)/c(—COO^-)等于0.5时为最佳CMC用量,此时上清液中 去除率可以达到96%以上。

关键词: 羧甲基纤维素钠, 铜离子, 紫外分光光度法, 螯合, 稳定常数