Pressure leaching of synthetic zinc silicate in sulfuric acid medium

The pressure leaching of synthetic zinc silicate is studied in the present paper. Five key parameters were explored, namely, sulfuric acid concentration, the final pH of leaching pulp, leaching temperature, water content and iron addition. The experimental results obtained show that sulfuric acid concentration, the final pH, iron addition, water content and leaching temperature have significant effect on the leaching behavior of zinc and silica. Higher leaching temperature and final pH improved filtration characteristics of the leaching pulp. The final pH affected the co-precipitation of silica and iron (III) oxide. Once all these five parameters were optimized, the Zn extraction percentage was found to be as high as 97% and the extent of Si dissolution as low as 0.6%; the filtration rate increased to 1057L/m2·h. The kinetic study showed that the leaching process follows shrinking core model with diffusion control with an apparent activation energy of 16.4kJ/mol in the temperature range of 110–170°C. The empirical reaction order with respect to the concentration of sulfuric acid is 1.0, which is also consistent with a diffusion-controlled process.