Factorial design for process optimization and generation of kinetic data for yttrium and europium leaching

Abstract

Factorial design has been implemented to develop regression equations for leaching of Y and Eu from phosphor coating of spent fluorescent lamps (FLs). On the basis of leaching extent, H₂SO₄ was the most suitable lixiviant. Parameter chosen for 2³ full factorial design were temperature, H₂SO₄ concentration and pulp density. Leaching extent obtained at design conditions were fed to Minitab and regression equations for time intervals namely 1, 2, 3 and 4 h were generated. Experiments were carried out to validate equations and results were within ±5% w/w of calculated values. These equations were solved for 99.9–100% leaching and obtained conditions have been represented as response surfaces. More than 99% of Y and Eu can be leached with H₂SO₄ of concentration 6–9.3% v/v at temperature 70–95°C and pulp density 5–20% w/v in 3 h.Leaching extents required for kinetic studies were also determined from regression equations.