The present invention discloses a method for decomposing medium-/low-grade scheelite, specifically comprising steps of: grinding medium-/low-grade scheelite, decomposing in an autoclave by using sodium phosphate and activated magnesium fluoride as leaching agents, and treating by solid-liquid separation to obtain crude sodium tungstate solution and residue. In this way, the medium-/low-grade scheelite is decomposed. Magnesium chloride is added in a sodium fluoride solution to prepare activated magnesium fluoride as a leaching agent. The present invention has the advantage that the high-efficiency decomposition of medium-/low-grade scheelite can be realized with low consumption of leaching agents, and the leaching cost can be greatly reduced in comparison to the existing decomposition processes using sodium hydroxide and sodium carbonate. This process is short in route, simple in operation, readily available and reliable in production equipment, and easy for industrialization.

The present invention discloses a method for decomposing medium-/low-grade scheelite, specifically comprising steps of: grinding medium-/low-grade scheelite, decomposing in an autoclave by using sodium phosphate and activated magnesium fluoride as leaching agents, and treating by solid-liquid separation to obtain crude sodium tungstate solution and residue. In this way, the medium-/low-grade scheelite is decomposed. Magnesium chloride is added in a sodium fluoride solution to prepare activated magnesium fluoride as a leaching agent. The present invention has the advantage that the high-efficiency decomposition of medium-/low-grade scheelite can be realized with low consumption of leaching agents, and the leaching cost can be greatly reduced in comparison to the existing decomposition processes using sodium hydroxide and sodium carbonate. This process is short in route, simple in operation, readily available and reliable in production equipment, and easy for industrialization.

The present invention provides a method for selective recovery of a valuable metal from a waste denitrification catalyst through alkali fusion, the method comprising the steps of: (a) adding an alkali metal to a waste denitrification catalyst, followed by mixing and alkali fusion, to generate a calcination product; (b) subjecting the calcination product to water-leaching to recover an alkali leachate and a residue; (c) adding a precipitator to the alkali leachate, followed by stirring, to recover calcium metavanadate (Ca(VO.sub.3).sub.2) or calcium tungstate (CaWO.sub.4) through precipitation; and (d) subjecting the recovered calcium tungstate to acid decomposition to prepare tungstic acid. Therefore, vanadium and tungsten can be recovered at high efficiency by a method in which a precipitator is added to a leachate, which is obtained by adding an excess amount of an alkali metal to a waste denitrification catalyst and carrying out calcination and water-leaching, and then a reaction rate is controlled.

The present invention relates to a method for leaching precious metals contained in a waste denitrification catalyst by using a pressure leaching process, and more specifically, to a method for leaching precious metals contained in a waste denitrification catalyst by using a pressure leaching process, the method comprising the steps of: forming a mixture by mixing a waste denitrification catalyst with a sodium salt solution; and leaching vanadium and tungsten contained in the mixture by feeding the mixture into a sealed pressurized reactor, and then heating and stirring the mixture.

This invention relates to a method for controlling exothermic reactions between metal chlorides of Zn, V, Cr, Co, Sn, Ag, Ta, Ni, Fe, Nb Cu, Pt, W, Pd, and Mo, and Al and the use of the method for preparation of metallic alloys and compounds based on base metals Zn, V, Cr, Co, Sn, Ag, Ta, Ni, Fe, Nb Cu, Pt, W, Pd, and Mo. The method provides for a mixture of precursor chemicals including at least one solid base metal chloride to be mixed and reacted exothermically with a control powder based on Zn, V, Cr, Co, Sn, Ag, Ta, Ni, Fe, Nb Cu, Pt, W, Pd, and Mo and then reacting the resulting intermediates with an Al scavenger. Reduction is carried out in a controlled manner to regulate reaction rates and prevent excessive rise in the temperature of the reactants and the reaction products.

The invention relates to a method for preparing high-melting-point metal powder through multi-stage deep reduction, and belongs to the technical field of preparation of powder. The method includes the following steps of mixing dried high-melting-point metal oxide powder with magnesium powder and performing a self-propagating reaction, placing an intermediate product into a closed reaction kettle, leaching the intermediate product with hydrochloric acid as a leaching solution so as to obtain a low-valence oxide Me.sub.xO precursor of the low-valence high-melting-point metal; uniformly mixing the precursor with calcium powder, pressing the mixture, placing the pressed mixture into a vacuum reduction furnace, heating the vacuum reduction furnace to 700-1200 C., performing deep reduction for 1-6 h, leaching a deep reduction product with hydrochloric acid as a leaching solution and performing treatment, so as to obtain the high-melting-point metal powder.

The present invention discloses a method for decomposing medium-/low-grade scheelite, specifically comprising steps of: grinding medium-/low-grade scheelite, decomposing in an autoclave by using sodium phosphate and activated magnesium fluoride as leaching agents, and treating by solid-liquid separation to obtain crude sodium tungstate solution and residue. In this way, the medium-/low-grade scheelite is decomposed. Magnesium chloride is added in a sodium fluoride solution to prepare activated magnesium fluoride as a leaching agent. The present invention has the advantage that the high-efficiency decomposition of medium-/low-grade scheelite can be realized with low consumption of leaching agents, and the leaching cost can be greatly reduced in comparison to the existing decomposition processes using sodium hydroxide and sodium carbonate. This process is short in route, simple in operation, readily available and reliable in production equipment, and easy for industrialization.

The present invention discloses a method for decomposing medium-/low-grade scheelite, specifically comprising steps of: grinding medium-/low-grade scheelite, decomposing in an autoclave by using sodium phosphate and activated magnesium fluoride as leaching agents, and treating by solid-liquid separation to obtain crude sodium tungstate solution and residue. In this way, the medium-/low-grade scheelite is decomposed. Magnesium chloride is added in a sodium fluoride solution to prepare activated magnesium fluoride as a leaching agent. The present invention has the advantage that the high-efficiency decomposition of medium-/low-grade scheelite can be realized with low consumption of leaching agents, and the leaching cost can be greatly reduced in comparison to the existing decomposition processes using sodium hydroxide and sodium carbonate. This process is short in route, simple in operation, readily available and reliable in production equipment, and easy for industrialization.

The present invention discloses a method for effectively decomposing mixed wolframite and scheelite ore in an alkaline system, specifically comprising steps of: grinding mixed wolframite and scheelite ore, putting in an autoclave, adding an appropriate amount of water, and then adding sodium phosphate, sodium hydroxide and calcium fluoride for decomposition, and treating by solid-liquid separation to obtain crude sodium tungstate solution. The present invention has the advantage that the high-efficiency decomposition of the mixed wolframite and scheelite ore can be realized with low consumption of leaching agents. By this method, the mixed wolframite and scheelite ore can be directly treated by an existing tungsten smelting autoclave, with low leaching cost, high decomposition rate and easy industrial application.

The present invention discloses a method for effectively decomposing mixed wolframite and scheelite ore in an alkaline system, specifically comprising steps of: grinding mixed wolframite and scheelite ore, putting in an autoclave, adding an appropriate amount of water, and then adding sodium phosphate, sodium hydroxide and calcium fluoride for decomposition, and treating by solid-liquid separation to obtain crude sodium tungstate solution. The present invention has the advantage that the high-efficiency decomposition of the mixed wolframite and scheelite ore can be realized with low consumption of leaching agents. By this method, the mixed wolframite and scheelite ore can be directly treated by an existing tungsten smelting autoclave, with low leaching cost, high decomposition rate and easy industrial application.