TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Method: Ferrochrome is high-carbon ferrochrome, carbon ferrochrome or low-carbon ferrochrome ground into more than 50 meshes fine powder (or taking carbon ferrochrome smelting molten fine powder more than 50 meshes), and placing in a reaction kettle, adding sufficient amount of hydrochloric acid or sulfuric acid, heating at 15-100 degrees C, full stirring, dissolving and reacting, making ferrochrome completely generate ion (chromium(III) ion, ferric (II) ion) solution, hydrogen collecting, preparing energy hydrogen production. In the method, adding ion containing water-soluble substance containing chromium, ferric ion solution precipitate as silicon, suspended substance as carbon, filtering solution, obtaining filter liquid and filter residue, obtaining filter residue, washing, separating, drying, preparing product silicon and carbon, preparing polycrystalline silicon product and silicon, filter liquor is chromium, ferric metal ion containing solution. In the method, adding oxalic acid in filter liquid complete precipitation for ferric ion which is ferrous oxalate, filtering, washing, crystallizing, drying, preparing product ferrous oxalate, filtered liquid is chromium ion solution and trace elements, adding thiram or sodium sulfide, removing metal ion and other trace, to obtain filter containing chromium ion filtered liquid. In the method, adding filtrate with ferrocyanide or ferricyanide salt, solution ferric ion complete precipitation is prussian blue or indigo blue, filtering, washing, drying prepared product, filtrate is chromium ion containing solution. In the method, adding filtrate with ferrocyanide or ferricyanide salt and soluble salt of copper ion, zinc ion, manganese ion, carbonate ion, nickel ion, yttrium ion, titanium ion, lead ion, cerium ion, cesium ion, cadmium ion, lanthanum ion, gallium ion, bismuth ion, zirconium ion, indium ion, tin ion, generating ferrocyanide derivative or ferricyanide salt derivatives, filtering, washing, drying to obtain product ferrocyanide derivative or ferricyanide salt derivatives, filtered liquid is chromium ion solution. Chromium ion solution prepared into different products (i) chromium ion solution is evaporated and dried to obtain goods and trivalent chromium salt, (ii) chromium ion solution is added with carbonate, bicarbonate, hydroxide, aqueous ammonia, chromium ion complete precipitate as chromium hydroxide, filtering, washing, crystallizing, drying, prepared product chromium hydroxide, high temperature sintering preparing product chromium oxide, (iii) chromium ion solution is added with special reflecting substance, carbonate (X2CO4), sulfate, hydrogen peroxide, oxygen, oxidation salt, permanganate, hypochlorite, carbonate (X2CO3), base (XOH), stirring, heating, carrying out oxidation reaction, using solution of chromium oxide solution is chromium(VI) ion, prepare chromate solution or bichromate solution, (a) using chromate solution or bichromate solution, evaporation and crystallizing, separating, drying, prepared product chromate or bichromate, (b) adding chromate solution with acidified (sulfuric acid, carbonization, electrolysis) using chromate solution complete generating bichromate solution, evaporation crystallizing, separating, drying, preparing bichromate product. In the method, adding filter liquor containing ferric ion, chromium ion solution with special reflecting substance, carbonate (X2CO4), sulfur, hydrogen peroxide, oxygen, the oxidation salt, permanganate, hypochlorite, carbonate (X2CO3), base, stirring heating, carrying out oxidation reaction, using solution of chromium oxide is chromium(VI) ion, preparing chromate solution or dichromate solution, using solution of ferric ion complete precipitate as ferric hydroxide, (i) using chromate solution or bichromate solution, evaporating and crystallizing, separating, drying, and preparing chromate or bichromate product, (ii) adding chromate solution with acidified (sulfuric acid, carbonization, electrolysis) using chromate solution complete generating bichromate solution, evaporation crystallizing, separating, drying, preparing bichromate product, (iii) containing hexavalent ferrochromium hydroxide into the acid, adding reducing agent ferric sulfate, disodium sulfate, sodium bisulfite, sodium metabisulfite, sodium sulfide, making chromium(VI ) ion is reduced to chromium(III) ion, adding alkali generating ferric hydroxide and chromium hydroxide precipitate, separating, filtering, washing, drying, preparing product of ferric hydroxide and chromium hydroxide.