Recovery of tungsten values from tungsten-bearing materials

Description

[0001] Tungsten is generally found in nature in scheelite type ores and wolframite type ores. These two ores differ substantially in their chemical composition being a calcium tungstate and an iron-manganese tungstate, respectively. Consequently, different processes have generally been used to recover the tungsten values from each type of ore. In the case of scheelite ores, the classical prior art process is to treat the ore with hydrochloric acid to produce insoluble tungstic acid. The tungstic acid is taken up in an ammonia solution to produce ultimately ammonium paratungstate (APT). Wolframite on the other hand is usually decomposed by fusing the ore with sodium hydroxide/sodium carbonate which extracts the tungsten as sodium tungstate. The cooled fused product is leached with water to extract the soluble sodium tungstate. Similarly, this may be treated with hydrochloric acid to precipitate tunstic acid which is taken up in an ammonia solution to produce APT.

[0002] British patent specification No. 1,089,913 describes a process for recovering tunsten values from both scheelite and wolframite type ores or concentrates. This process comprises fusing powdered scheelite and/or wolframite type ores or concentrates with a fluxing mixture of sodium carbonate, sodium chloride and sodium nitrate (which mixture also contains, in the case of the starting material containing calcium, at least sufficient siliceous material to form calcium silicate therewith), leaching the cooled, fused material with water and separating a tungsten-bearing alkaline leach liquor from water-insoluble impurities, acidifying the separated leach liquor and adding thereto sufficient of a fluoride or hydrofluoric acid to form compounds which are substantially insoluble in organic media, extracting the thus-treated material with an organic solution comprising an organic amine capable of forming a water-insoluble organic amine tungsten complex to transfer tungsten from the aqueous to the organic phase, separating the phases, treating the separated organic phase, with aqueous ammonia to form a water-soluble ammonium tungstate, and separating the aqueous phase containing ammonium tungstate from the organic phase. This process involves, as an essential step, the fusion of powdered scheelite and/or wolframite type ores or concentrates with a mixture of sodium carbonate and sodium chloride. Indeed, it is stated in the specification that a fluid melt should be produced. Typical temperatures at which the fusion take place are 698°C to 825°C.

[0003] Fox U.S. Patent No. 3,800,025 describes a process of extracting tungsten values from low grade tungsten ores which includes the steps of roasting a particulated tungsten-containing ore in a water containing atmosphere in the presence of sodium chloride and at least one of the reagents selected from sodium carbonate and sodium phosphate at a temperature in the range of about 600°C to about 900°C for about 1 to 3 hours, water leaching the resulting calcines to dissolve soluble tungsten values and filtering. This process is restricted in application to low grade tungsten ores and requires a water containing atmosphere for its operation. Moreover, relatively high roast temperatures and relatively low amounts of sodium reactant are generally used.

[0004] French Patent Specification 992821 describes a process for extracting tungsten values from low grade tungsten-containing slags in which a mixture of crushed slag and an alkali metal salt is roasted at a temperature below the melting point and the roasted product is leached in order to extract tungsten values.

[0005] We have now developed an improved method of recovering tungsten values from mixtures of wolframite and scheelite.

[0006] According to the present invention, we provide a method of recovering tungsten values from a tungsten-bearing ore or concentrate in which the ore or concentrate is roasted, without fusion, in the presence of a reagent which is an alkali metal chloride or carbonate or a mixture thereof and water-soluble tungsten values are extracted from the roasted product, characterised in that the tungsten bearing ore or concentrate is a high grade ore or concentrate which is a mixture of wolframite and scheelite and that after extraction of the water-soluble values from the roasted product, the latter is roasted again, without fusion, in the presence of the reagent and further water-soluble tungsten values are extracted from the re-roasted product.

[0007] It is essential to the process that roasting takes place without general fusion, that is the mix of ore or concentrate and reagent must not form a fluid melt during roasting. The fact that a melt is not produced confers a much greater flexibility in process design and can result in energy savings. The roasted product is an easily handleable material.

[0008] The tungsten values in the roasted product will be in the form of water-soluble alkali metal tungstate. This product may thereafter be treated in known manner to recover the tungsten values as tungsten metal. For example, the tungsten values may be water leached from the roasted mixture and the leach liquor then treated in the manner described in British patent specification No. 1,089,913. These treatment steps are essentially an application of chemistry known in the art.

[0009] The tungsten-bearing ore or concentrate is α^- high grade one, i.e. one containing at least 20 percent by weight tungsten as tungsten oxide (W0₃). Such materials may contain up to 80.5 percent by weight tungsten as tungsten oxide.

[0010] The reagent is an alkali metal chloride, an alkali metal carbonate or a mixture thereof. The alkali metal for both the chloride and the carbonate reagent is preferably sodium. It is a particularly preferred feature of the process that the reactive composition consists solely of an alkali metal carbonate, such as sodium carbonate. It has surprisingly been found that excellent tungsten recoveries, at relatively mild temperatures can be achieved using sodium carbonate alone.

[0011] The roasting temperature will vary according to the nature of the ore or concentrate being treated and the type and quantity of reagent. The important point is that a temperature must be chosen which will not result in fusion bf the mixture of ore or concentrate and reagent taking place, but will yet be high enough for the desired reaction to take place in a reasonable time. As a general rule temperatures in the range 600° to 800°C will be used.

[0012] The step of re-roasting the extracted material in the presence of further reagent and extracting tungsten values from the re-roasted material can be repeated until as much of the tungsten as desired has been extracted from the ore.

[0013] The amount of reagent present during roasting will also vary according to the nature of the ore or concentrate. There should be at least sufficient sodium present to combine with all the tungsten to form sodium tungstate and it is generally preferred to use a stoichiometric excess of sodium.

[0014] The roasting must take place for a sufficient time to convert as much as possible of the tungsten to sodium tungstate. The roasting time is typically up to 120 minutes, although for many ores no particular advantage has been found by heating for a period of longer than 60 minutes.

[0015] Where necessary, depending on the ore composition and/or type of heating equipment being used, the reagent may also contain a suitable oxidising agent, such as sodium nitrate. It may be desirable in some cases to include finely divided silica in the reactive composition. The silica reacts with the calcium to form tricalcium silicate which is subsequently readily separable from the sodium tungstate.

[0016] The tungsten-bearing ore or concentrate and the reagent will generally both be provided in finely divided state and will be intimately mixed prior to roasting. After roasting, the product may be leached with water. It has been found experimentally that one leach and a replacement wash under appropriate conditions are generally sufficient. The fact that there is no fusion during roasting means that leaching may take place on the roasted product as such without subjecting that product to a crushing or like step. Moreover, leaching may take place while the roasted product is still hot.

[0017] After leaching, the leach liquor is treated by commonly known methods to remove impurities such as aluminium, magnesium, phosphorous, silicon, antimony, arsenic and molybdenum.

[0018] After the first purification step, the filtrate may be further purified by treatment with a fluoride or hydrofluoric acid. The adequately purified solution is then subjected to a conventional solvent extraction procedure. The tungsten contained in the organic phase may be extracted with ammonium hydroxide to provide an aqueous ammonium tungstate solution.

[0019] Tungsten metal powder may be produced from the ammonium tungstate by known methods.

[0020] In order that the invention may be more fully understood, the following example is given by way of illustration.

[0021] In this exampfe, the ore (or extracted residue) and reagent was in finely divided or particulate form and was roasted as a mixture. After roasting, the sodium tungstate was leached with water, the residue separated from the leach liquor by filtration and washing and the leach liquor treated in the manner generally described above to recover the tungsten values.

Example

[0022] A scheelite concentrate containing 74.8% of W0₃ and a wolframite concentrate containing 68.1% W03 were mixed 1:1 by weight and the mixture was mixed with sodium carbonate in the proportion of 1 part of sodium carbonate to four parts of the mixture. The specific quantities used were 300 g of scheelite, 300 g of wolframite and 150 g of sodium carbonate (the theoretical stoichiometric amount of sodium carbonate was 98 g). The final mixture was roasted at 650°C for four hours. After roasting, the material was leached with water as described above to give a percentage extraction of tungsten of 58%.

[0023] The extracted residue was again mixed with sodium carbonate and roasted at 650°C and two tests conducted with different amounts of sodium carbonate. The results are given in Table I.

[0024] The overall tungsten extraction is 90 and 95 percent at residue: Na₂CO₃ ratios of 7:3 and 1:3. The particular ratio chosen will depend on the particular economic circumstances under which-the process is, operated at any given time.

Claims

1. A method of recovering tungsten values from a tungsten-bearing ore or concentrate in which the ore or concentrate is roasted, without fusion, in the presence of a reagent which is an alkali metal chloride or carbonate or a mixture thereof and" water-soluble tungsten values are extracted from the roasted product, characterised in that the tungsten-bearing ore or concentrate is a high grade ore or concentrate which is a mixture of wolframite.and scheelite and that after extraction of the water-soluble values from the roasted product, the latter is roasted again, without fusion, in the presence of the reagent and further water-soluble tungsten values are extracted from the re-roasted product.

2. A method according to claim 1 characterised in that the roasted product is leached with water while it is hot in order to extract tungsten values therefrom.

Revendications

1. Procédé de récupération de sels de tungstène à partir d'un minerai ou d'un concentré contenant du tungstène, selon lequel on grille le minerai ou le concentré, sans fusion, en présence d'un réactif qui est un chlorure ou un carbonate d'un métal alcalin, ou un mélange de ces corps, puis on extrait les sels de tungstène du produit grillé, caractérisé en ce qu'on part d'un minerai ou d'un concentré contenant du tungstène d'un grade élevé qui est un mélange de wolframite et de scheelite et que, après extraction des sels de tungstène solubles dans l'eau du produit grillé on grille ce dernier à nouveau sans fusion en présence du réactif et on extrait du produit regrillé des sels de tungstène supplémentaires.

2. Procédé selon la revendication 1 caractérisé en ce qu'on traite le produit grillé par lixiviation à l'aide d'eau pendant qu'il est chaud afin d'en extraire des sels de tungstène.

Ansprüche

1. Verfahren zum Gewinnen bzw. Wiedergewinnen von Wolfram aus einem wolframhältigen Erz oder Konzentrat, wobei das Erz oder Konzentrat ohne zu schmelzen in Gegenwart eines Reagens, das ein Alkalimetall-Chlorid oder -Karbonat oder eine Mischung davon ist, geröstet und aus dem Röstprodukt wasserlösliche Wolframverbindungen extrahiert werden, dadurch gekennzeichnet, daß ein hochwertiges wolframhältiges Erz oder Konzentrat verwendet wird, das eine Mischung aus Wolframit und Scheelit darstellt, und daß nach der Extraktion der wasserlöslichen Wolframverbindungen aus dem Röstprodukt dieses letztere abermals ohne zu schmelzen in Gegenwart des Reagens geröstet wird und weitere wasserlösliche wolframhältige Verbindungen aus dem wiedergerösteten Produkt extrahiert werden.

2. Verfahren nach Anspruch 1, dadurch gekennzeichnet, daß das Röstprodukt noch in heißem Zustand mit Wasser gelöscht wird, um die Wolframverbindungen zu extrahieren.