【China Molybdenum Industry News Network】
The molybdenum solution is then filtered free from the mixed precipitate formed, and calcium, iron, or other chloride is added to the sodium molybdate solution. The solution is heated to boiling temperature and simultaneously agitated, until the molybdenum present is substantially all precipitated as calcium, iron, or other, molybdate. The molybdate precipitated is then filtered, washed and dried.
If an objectionably large proportion of sulphur is present, it is advantageous to wash the precipitated molybdate with a considerable volume of warm water (optimum temperature about 350 C.) after decanting the waste solution and before the final filtering.
An important advantage of the use of NaN03 as decomposition agent is that, if any excess of NaN03 remains undecomposed by the initial sintering, this excess cannot react with CaC12 and thus contaminate the CaMoO4 with any by-product. This advantage is most apparent by contrast with both sulphide and sulphate reagents, an excess of which would produce CaS or CaSO4, both of which are particularly objectionable in CaMoO4; but NaN03 is also almost equally advantageous as compared with carbonate or hydroxide reagents, by avoiding the formation of CaCOs or Ca(OH)2 during the precipitation of CaMoO4 by CaC12.
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