Investigation of cadmium cementation kinetics in the presence of surfactants

The aim of the paper is to study the kinetics of cadmium cementation with zinc powder in aqueous media in a continuous mode using an ion-selective cadmium electrode. Reduction of cadmium from aqueous solutions was carried out with zinc powder, with particle sizes from 63 to 200 μm. In a number of experiments, the influence of the cationic flocculant Besfloc K6645 on the cadmium cementation process was tested. The process was carried out in the temperature range from 30 to 50 °C with continuous stirring at 200 rpm with an overhead stirrer. Kinetic curves were recorded using a cadmium-selective electrode. The kinetic curves were conditionally divided into linear segments. Tangents were drawn to each section, which made it possible to determine the apparent rate constants using the first-order equation, as well as the mode coefficients using the Erofeev-Kolmogorov equation. An increase in temperature had a positive effect on cementation. The introduction of a flocculant into the electrolyte in the amount of 70 mg/L reduced the degree of cementation from two to three times over a period of 600 s. The data obtained made it possible to calculate the activation energies of the process rates on the linear sections of the kinetic curves, which amounted to approximately 46, 32 and 11-13 kJ/mol in the first, second, and third sections, respectively, for reduction without the addition of a flocculant, as well as 117-130 and 82-85 kJ/mol in the presence of Besfloc K6645 flocculant. It has been shown that in the presence of a flocculant, the activation energy increases, especially in the first section, which is characterized by a slow cementation rate. The study demonstrates the effect of the Besfloc K6645 additive on the duration of the initial section of the cementation kinetic curves.