| 摘要 |
A method of purifying anhydrous soda ash containing sodium fluoride as an impurity so as substantially to remove the sodium fluoride, e.g. to level less than 0.03% w/w comprises the steps of (i) milling the crude, anhydrous soda ash; (ii) admixing the milled, crude anhydrous soda ash with a saturated solution of sodium carbonate under conditions forming a heated admixture at a temperature which is below about 112‹C and which provides formation of sodium carbonate monohydrate crystals; (iii) effecting a separation by size of sodium fluoride and the sodium carbonate monohydrate crystals; (iv) heating an aqueous slurry of the sodium monohydrate crystals from (iii) to a temperature above about 112‹C at which the sodium carbonate monohydrate crystals are converted into the anhydrous form; (v) cooling the slurry to a temperature below about 112‹C so as to convert the anhydrous crystals from step (iv) to sodium carbonate monohydrate crystals; (vi) effecting a separation by size of the sodium carbonate monohydrate crystals from step (v) from sodium fluoride, and (vii) recovering the sodium carbonate monohydrate crystals. |
