Tungsten ore tailings

Flexible — the process developed should be applicable to a broad range of compositions found in tungsten ore tailings. 

The sodium tungstate is the process solution from which the tungsten is recovered by further treatment. The insoluble hydroxides are filtered off and constitute the tungsten ore tailings, the subject of this study. The tailings are usually stored in a self-contained site prior to ultimate disposal. 

Table L Typical Elemental Competition of the Tungsten Ore Tailings...

The results of the first dissolution experiments have shown that the tungsten ore tailings do not have a homogeneous composition but are a complex material consisting of a variety of constituents with different stoichiometry, structure, chemical reactivity, and solubility. Thus, the weight fractions reported in Tables I and II are macro representations of the overall sample content but do not imply that these constituent ratios can be found uniformly in every particle throughout its mass. 

Acid Dissolution. In view of the fact that the oxides of two transition metals, Fe and Mn, account for 65% of the mass of the tungsten ore tailings, acids are the obvious choice for material dissolution. It was found that concentrated HCl dissolves up to 80% of the total mass, including nearly all of the Fe, Mn, and Sc content, leaving behind a residue which is quite different in nature. While the starting material is black, soft, and fairly reactive, the insoluble residue obtained from the acid digestion, the so-called acid residue, is much lighter in color, sandy in texture, and unreactive. It contains primarily W, Si, Nb, Ta, and other acid-insoluble constituents. 

Table IV. Acid-Soluble Fe and Mn in Tungsten Ore Tailings Size Fractions ...

While the alkaline digestion of wolframite ores results in the formation of Mn(OH)2 (equation 1) in which Mn is divalent, the presence of Mn02 in the ore tailings is not surprising because the air oxidation of Mn(OH)2 is well known (5). Extensive observations of the dissolution behavior of the tungsten ore tailings indicate that it is not a simple acid dissolution but a redox reaction such as... 

The key trends observed in the dissolution of tungsten ore tailings are independent of the reductant system or sample variation. These are the following ... 

The experimental evidence obtained indicates that the thr key constituents may be segregated within the tungsten ore tailings whose acid-soluble fraction consists of three major phases ... 

The objective of this effort was the initial recovery of Sc with subsequent process steps to separate and recover the other metallic constituents. The initial step was the acid digestion of the tungsten ore tailings, which produced an insoluble residue containing W and a solution rich in most of the other metals. The steps in the overall separation scheme are outlined by the flow sheet presented in Figure 3. The hydrazine/ sulfuric acid solution was chosen as the reductant/solvent reagent based on the following considerations ... 

The scandium recovery process is ouUined schematically in Figure 5. The tungsten ore tailings are dissolved in the hydrazin sulfuric reagent, the pH is adjusted to 2.0, and the resulting solution is checked for the presence of ferric ion colorimetrically using the thiocyanate spot test. Any ferric ion content is reduced to the ferrous state by the addition of elemental iron as per the following equation ... 

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