Quartz Dissolution as Influenced by pH and the Presence of a Disturbed Surface Layer

Abstract

AbstractQuartz particles (10 to 2 microns in diameter, produced by grinding) released 45 ppm of SiO2 to a buffer solution of pH 7 during a 48 hr period. The grinding of quartz particles produced a disturbed surface layer with solubility properties intermediate between crystalline quartz (6 ppm SiO2) and amorphous silica (120 ppm SiO2). Removal of the disturbed layer by treatment with 1N HF lowered the SiO2 dissolution from 45 to 3 ppm. Use of 12N HF decreased the amount of SiO2 dissolved to 2 ppm, a result found to coincide with a preferential dissolution of the finer quartz particles in addition to the removal of the disturbed surface layer. The rate of dissolution of SiO2 from quartz particles, subsequent to treatment with 1N HF, increased with decrease in particle size, from 1 to 3 ppm for quartz particles 50 to 20 microns in diameter to 30 to 44 ppm for particles 2 to 0.2 microns in diameter, during each of three consecutive 14‐day extractions with pH 7 buffer solution. The amount of SiO2 dissolved from quartz in buffer solutions increased in the pH range of 4 to 10, from 0.6 ppm of SiO2 at pH 4 to 19 ppm at pH 10 during a 14‐day period of extraction from quartz particles, 10 to 2 microns in diameter. Quartz particles, subsequent to the removal of the disturbed surface layer, removed SiO2 from pH 4 and pH 8 buffer solutions prepared with more SiO2 in solution than would be released from quartz in the respective solution.