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正常条件下,Cr(Ⅲ)与 EDTA 在 pH3.5±0.2缓慢形成紫色络合物。该反应可以用超声波来催化。用强度为1.5W/cm~2的超声波照射7.5分钟,络合物可迅速定量形成。该方法已成功地应用于原矿及选矿样品中20—60%Cr_2O_3的测定而无需分离基体元素。铬的比色分析是将 Cr(Ⅲ)氧化成 Cr(Ⅵ)后再进行络合,即使是原子吸收分光光度法或 ICP 法也都着眼于 Cr(Ⅵ)上。相比之下,用 Cr(Ⅲ)比色的测定方法因为其取代反应缓慢而不为人们所重视。Cr(Ⅲ)与多元羧酸(DCTA,NTA,EDTA)之间的反应很慢。Cr(Ⅲ)与乙二胺四乙酸(EDTA)在 pH3—5.2范围内可缓慢形成紫色的络合物 H[Cr(EDTA)—(H_2O)]。但是加入碳酸氢根离子,锰盐或煮沸溶液30分钟都可增加络合速度。最近,超声波对化学反应的作用成了研究的焦点,高强度超声波可以加速常规条件下发生的化学反应,还可以引发常规条件下根本不可能发生的化学反应。Irving 曾报道,将锌粒直接加到含过量 EDTA 溶液中,新产生的二价铬离子可催化 Cr(Ⅲ)与 ESTA 的络合反应。但在以后实验中发现.在高浓度硫磷酸盐存在下,加碳酸氢盐或锌粒,Cr(Ⅲ)与 EDTA的络合不能定量进行。本文尝试用超声波照射催化 Cr(Ⅲ)与 EDTA 的络合反应,并将其推广应用于原矿及选矿样品中铬的测定。
Under normal conditions, Cr (III) and EDTA slowly form a purple complex at pH 3.5 ± 0.2. The reaction can be catalyzed by ultrasound. With the intensity of 1.5W / cm ~ 2 ultrasonic irradiation for 7.5 minutes, the complex can be quickly quantitatively formed. The method has been successfully applied to the determination of 20-60% Cr 2 O 3 in raw ore and beneficiation samples without separation of matrix elements. The colorimetric analysis of chromium is the oxidation of Cr (III) to Cr (VI) followed by complexation, even though the atomic absorption spectrophotometry or ICP method also focuses on Cr (VI). In contrast, with Cr (Ⅲ) colorimetric determination method because of its slow substitution and not as people pay attention. The reaction between Cr (III) and polycarboxylic acids (DCTA, NTA, EDTA) is very slow. Cr (Ⅲ) and ethylenediaminetetraacetic acid (EDTA) slowly formed the purple complex H [Cr (EDTA) - (H_2O)] in the range of pH3-5.2. However, adding bicarbonate ions, manganese salts or boiling solution for 30 minutes can increase the rate of complexation. Recently, the role of ultrasound in chemical reactions has become the focus of research. High-intensity ultrasound can accelerate the chemical reactions that occur under normal conditions and lead to chemical reactions that would otherwise not occur under normal conditions. Irving has reported that the addition of zinc particles directly to an excess of EDTA solution resulted in the formation of a new chromium (II) ion that catalyzed the complexation of Cr (III) with ESTA. However, it was found in later experiments that the complexation of Cr (Ⅲ) with EDTA could not be quantified in the presence of high concentrations of thiophosphate with bicarbonate or zinc particles. In this paper, we try to catalyze the complexation of Cr (Ⅲ) with EDTA by ultrasonic irradiation and apply it to the determination of chromium in ore and ore dressing samples.