| 摘要 |
<p>The present invention relates to a method for recovering boric acid from a liquid to be treated containing either waste water or solid waste comprising boron compounds and alkali metal compounds, wherein the liquid to be treated is concentrated after an acid is added to the liquid to be treated and the pH is adjusted to less than 4, or an acid is added to the liquid to be treated and the pH is adjusted to less than 4 after the liquid to be treated is concentrated, the concentrated and pH-adjusted liquid to be treated not containing insoluble materials is cooled to form an aqueous solution in which boric acid crystals are precipitated, the boric acid crystals are separated from the aqueous solution in which boric acid crystals are precipitated, 50-90 mass% of the filtrate after separating the boric acid crystals is added to the liquid to be treated before concentration and pH-adjustment, a liquid to be treated for recrystallization which is formed by adding a boric acid aqueous solution or water to the separated boric acid crystals is heated to dissolve the boric acid crystals, the heated liquid to be treated for recrystallization in which the boric acid crystals are dissolved is cooled to form an aqueous solution in which boric acid crystals are reprecipitated, the boric acid crystals are separated from the aqueous solution in which boric acid crystals are reprecipitated, and at least a part of the filtrate after separating the reprecipitated boric acid crystals is added to the liquid to be treated before concentration and pH-adjustment.</p> |
