2001 Volume 34 Issue 2 Pages 232-235
The SiO2 concentrate after extracted of aluminum from clay from Sancheong-Hadong, Korea, was leached with NaOH at 25-100°C under atmospheric pressure. About 80% of the silicon in the concentrate was extracted at 25°C within 30 minutes. The molar SiO2/Na2O of the sodium silicate solution thus obtained ranged from 2.5 to 3.1. The silicate solution contains 0.11 wt.% of alminum and 67 ppm of iron as impurity. Out of 150 g of the concentrate charged, about 100 g was dissolved and the balance was undissolved. The filterability of the resulting slurray was studied in a pressure filter with varying pressures and temperatures. By analysis of the undissolved solid, the formation of insoluble sodium compounds during NaOH leaching is found to be negligible.