| 摘要 |
<p>Ammonium tungstate is made by heating Ca tungstate material at 900-1300 degrees C, in presence of a reducing agent, to form tricalcium tungstate and/or metallic tungsten. The obtd. material is treated with an aq. soln. contg. NH4+ ions and anions selected from CO32 and/or HCO3-ions at 30-70 degrees C in the presence of an excess of oxidising agent. The quantity of NH4+ ions is sufficient to react with the W values to form ammonium tungstate which is soluble in the soln. and the quantity of anions is sufficient to react with the Ca to form an insoluble Ca. cpd. The insoluble is then sepd. from the ammonium tungstate soln. The process may be operated as a batch and/or a continuous process Wolframite, scheelite, and/or Ca tungstate ores can be treated opt. in presence of Ca donor cpd. to produce ammounium tungstate which can subsequently be used to obtain, by redn., W trioxide or metallic W. The process is pollution-free and nay contaminants in effluent streams may be treated by known techniques.</p> |
