Investigation into the Influence of Flocculants on Kinetic Parameters of Reducing Copper in an Aqueous Solution by Metallic Zinc

Аннотация

A series of models is investigated for describing the reduction of copper by fine zinc powder in aqueous solutions. The experiments were performed in apparatuses with a magnetic stirrer at 15–50°C and stirring rates of 40–150 rpm. The influence of high-molecular flocculants such as nonionogenic magnafloc 333, cationic besfloc 6645, and anion besfloc 4034 on this process is investigated. These flocculants are applied under industrial conditions at the stage of hydrolytic purification of solutions and then enter the cementation purification along with the settled solution. Aqueous solutions of flocculants of 2.5 g/L with dosages of zinc dust of 2–4 g/L and flocculant of 50–200 mg/L are used in experiments. The copper content is determined quantitatively in initial and final solutions by spectrophotometric analysis with the preliminary transfer of copper into an ammonia complex. The experiment duration varied from 1 to 8 min. The degree of reduction of copper reduced from solutions was 10–90%. It is established that the process kinetics at low stirring rates can be described by the first-order equation. The kinetics of the heterogeneous reaction under study at high stirring rates in the presence of flocculants additives is most adequately described by the equation of the variation in the rate as the root square of the process duration. It is shown that the largest cementation rate constant is observed without adding surfactants. The cementation is retarded to a smaller degree in the presence of the anionic flocculant when compared with the cationic one, which agrees with the theory of electrochemical processes and shows that the discharge of copper cations under these conditions limits the cementation. The regularities of the process under study are retained with an increase in temperature. It is noted that the additions of high-molecular substances with a relative molecular mass of 20 million in an amount of 50–200 mg/L retard cementation. This fact should be taken into account under industrial conditions where cementation purification with the removal of copper and other impurities is performed from solutions containing flocculants.