Leaching of yttrium from cathode ray tube fluorescent powder: Kinetic study and empirical models

In this paper, leaching kinetics of yttrium from cathode ray tubes in sulphuric acid and hydrogen peroxide solution was investigated. It was found that hydrogen peroxide concentration, followed by temperature, has the greatest influence on leaching rate. Leaching rate is clearly enhanced by the increase in H2O2 concentration. The leaching process without hydrogen peroxide follows the kinetic model controlled by the chemical regime, whereas in presence of H2O2 it follows the kinetic model controlled by diffusion through the product layer. The apparent activation energy was determined to be 40.0 kJ/mol and 90.3 kJ/mol with and without hydrogen peroxide in solution, respectively. Moreover, the experimental data were used to describe empirical mathematical models in order to predict the yttrium extraction as a function of sulphuric acid concentration, hydrogen peroxide concentration, temperature and time. From the analysis of the results and models, the optimal conditions to maximize the extraction of yttrium were inferred: 40 °C, 10%vol hydrogen peroxide, 15 min of reaction with 15%wt/vol pulp density, or alternatively at higher temperature (80 °C) 15%wt/vol pulp density, 120-180 min with 0% or 5%vol hydrogen peroxide in solution. Hence, yttrium is easily leached from CRTs powder at low temperature (40 °C) with higher concentration of hydrogen peroxide, or by means of higher temperature (80 °C) and lower concentration, even null, of hydrogen peroxide.