Hydrothermal Treatment of Fluor-phlogopite.–Hydrothermal Treatment of Agglomerate Mass of Synthetic Mica Crystals to Facilitate Separation of Individual Crystals
Authors: Noda Tokiti , Saito Hajime , Tate Isao , Fukasawa Tsutomu , Fukase Masahiko , Sekine Eiji 
Published: July 2006

Abstract
Agglomerates of synthetic mica crystals were treated hydrothermally with alkali, acid and salt solutions in order to ease the separation of mica crystals which are bonded together by glassy substance.
(1) Among treatments with sodium hydroxide solutions of the concentration from 0.5 to 2 n at 350°C for 24 hr., that with 2n sodium hydroxide facilitated greatly the separation of mica crystals. A small amount of fluor-phlogopite probably changed to hydroxyl-phlogopite and hydroxides were produced by the hydro-thermal treatment.
(2) The hydration of fluor-phlogopite and the formation of hydroxide were suppressed by the addition of fluorides in the treating solution. It was found that the presence of 1.5 mol. potassium fluoride per liter of treating solution was effective for the suppression.
(3) Among treatments with potassium hydroxide solution in the presence of 2 mol. potassium fluoride per liter solution at 350°C for 24 hr., that with 0.25 n or more concentrated solution of potassium hydroxide was effective for easing separation of mica crystals. Potassium fluoride itself was found to be effective for easy separation.
(4) It was necessary to keep the temperature at 250°C or above in the treatment with 10 n potassium hydroxide and 300°C or above in the treatment with 0.5 n potassium hydroxide in order to obtain a good result.
(5) Treatments with potassium hydroxide solution in the presence of 2 mol. potassium fluoride per liter solution at 300°C for 24 hr. were as effective as those with the same solution at 350°C.
(6) Among treatments with solutions of various concentrations of potassium carbonate or potassium carbonate and potassium hydroxide at 250°C for 24 hr., 10 n or more concentrated potassium carbonate solution was effective as a treating solution and in a mixed solution of potassium carbonate and potassium hydroxide the latter played the main role.
(7) Among treatments with solutions of various concentrations of hydrochloric acid or hydrochloric acid and potassium chloride at 250°C for 24 hr., 0.125 n or more concentrated hydrochloric acid solution was effective as a treating solution and the presence of potassium chloride had no effect.
(8) Among treatments with potassium hydrogen sulfate, potassium hydrogen carbonate and potassium dihydrogen phosphate, that with potassium hydrogen sulfate was most effective and the smallest necessary concentration of the treating solution was 2 n.
(9) A solution of 7 n potassium fluoride or a more concentrated one was effective as a treating solution at 250°C for 24 hr.
(10) Split crystals from the mass treated with alkali and potassium fluoride solutions were flexible and those treated with acid were harder and less flexible than the former. The difference of the effects of acid and alkali was interpreted as the difference of their action on binding glass.
(11) Hydrothermal treatment for easy separation was much more effective on agglomerates of well developed crystals than on those of small crystals because the treating solution penetrates easily into the mass along plate crystals.
(12) Investigation of X-ray powder diagram of treated products revealed that the main part of fluor-phlogopite crystals remained unchanged and only a small amount of original mica changed to hydroxyl-phlogopite by treatments with strong alkali solutions. This observation was in good agreement with the experimental results deduced from the observed decreases of fluorine contents and temperature-weight loss curves of treated products.
(13) It was found that split crystals from a treated mass evolved less gas than those from an untreated mass because of the low content of adhering glass in the former. Split crystals which contained a small amount of hydroxyl-phlogopite began to evolve gas at about 950°C.