Iron removal from extremely fine quartz and its kinetics

The iron impurity removal from extremely fine quartz and its kinetics have been explored. The investigation reveals that the product layer diffusion in heterogeneous reaction system is the rate-control step and the activation energy was found to be 45.37 kJ/mol. But the mechanism seems to have a trend towards homogeneous reaction system with the second order rate model from the heterogeneous system. Because the homogeneous reaction system’s average linear correlation coefficient is up to 0.978, which is very close to 0.995 of its counterpart in heterogeneous system. This result was confirmed through examination of the homogeneous system models with the first and the second order rates, as well as the heterogeneous system models with interface film, product layer diffusion and chemical reaction models. Additionally, other interesting results revealed that the leaching efficiency for such extremely fine silica sand decreased with increasing stirring speed – this observation was opposite to that for coarse particles. Usually, leaching efficiency of coarse particles increases with increasing stirring speed or higher ultrasonic power.

► Rate control step of the highly purifying process is diffusion through product layer.
► The mechanism is very close to the second order reaction of homogeneous system.
► Opposite to coarse particles, leaching yield increased with decreasing stirring speed.