| 摘要 |
<p>1339471 Niobium MOLYBDENUM CORP OF AMERICA 1 Jan 1971 [5 Jan 1970] 28/71 Heading C1A A niobium concentrate is baked with sulphuric acid then treated with NH 3 or alkali metal hydroxide at pH >7 and temp. >25‹ C. then alkali metal hydroxide and water are added simultaneously or thereafter to produce a paste which is heated to form a water soluble complex which is aqueously leached in at least two stages and from which niobium values are obtained. The final stage may comprise crystallization, heating under CO 2 at superatmospheric pressure, or precipitation by the addition of mineral acid, and the product may be further purified by leaching with mineral acid. The aqueous leach may be carried out in two stages, in the first of which impurities only are removed. The product may be converted to Nb 2 O 5 by calcination.</p> |
