Method for integrated processing of titanium-containing feedstock to obtain high value-added products based on titanium, iron, calcium and nitrogen

A method for integrated processing of titanium-containing feedstock to obtain high value-added products based on titanium, iron, calcium and nitrogen, which comprises the following stages:

• a) digesting ilmenite concentrate, namely, decomposing a milled ilmenite concentrate with hydrochloric acid in two or more stages in a countercurrent system using a reducing agent, to obtain a solid residue and a solution of titanium oxychloride, which is sent to Stage c);
• b) processing the solid residue obtained in Stage a), which comprises:
• neutralization of the solid residue with ammonia water containing 3-25% NH4OH to produce a neutralization precipitate and a mother liquor,
• filtration of the mother liquor, washing the neutralization precipitate, drying the neutralization precipitate at a temperature of 100-200° C., and calcining the neutralization precipitate for 1-8 hours at a temperature of 300-1050° C.,
• obtaining the neutralization precipitate with a titanium dioxide content of more than 50% and the mother liquor, which is sent to Stage i);
• c) hydrolysis of titanium oxychloride {TiOCl2}from Stage a) to obtain a precipitate of titanium oxides/hydroxides with a specified particle size distribution, wherein the precipitate of titanium oxides/hydroxides remains suspended in the solution of titanium oxychloride to form a slurry of titanium oxides/hydroxides, wherein HCl vapor released during hydrolysis is captured and returned to Stage a) in the form of an aqueous solution of hydrogen chloride;
• d) washing the precipitate of titanium oxides/hydroxides during which the slurry of titanium oxides/hydroxides obtained in Stage c) is filtered to separate the precipitate of titanium oxides/hydroxides as a cake of titanium oxides/hydroxides, which is washed with purified water, then the cake of titanium oxides/hydroxides is sent to calcination stage e), and the mother liquor is sent to iron hydroxides precipitation stage f);
• e) calcination of the cake of titanium oxides/hydroxides at a temperature of 250-1000° C. for 0.5-10.0 hours to produce titanium dioxide, followed by cooling and milling of the resulting titanium dioxide;
• f) part of the mother liquor from Stage d) containing iron chlorides and free hydrochloric acid is mixed with milk of lime slurry with Ca(OH)2 content in the range between 5% and 35%, thereby neutralizing the hydrochloric acid and iron chlorides and forming a precipitate of iron hydroxide, the precipitate of iron hydroxide is oxidized with ambient oxygen for 5-40 hours, the slurry is cooled and filtered, the precipitate of iron hydroxide is washed and dried at a temperature of 30-80° C., after which a resulting black iron oxide pigment is obtained, which is subjected to milling, while at the same time an oxidizing agent is introduced into the mother liquor, which is then neutralized to a pH=7-12 with Ca(OH)2 to form a resulting mother liquor slurry, wherein the resulting mother liquor slurry is filtered to separate the precipitated iron hydroxide from the mother liquor to result in an iron hydroxide cake, then the iron hydroxide cake is dissolved using a hydrochloric acid solution, thus obtaining a solution of iron chloride FeCl3, with a pH in the range of 0.5-2.0, after which FeCl3 is reduced to FeCl2 using iron and the resulting solution of FeCl2 chloride is sent for mixing with solutions coming from Stage d), and the mother liquor is sent to Stage i) for processing;
• g) part of the mother liquor from Stage d) containing iron chlorides and free hydrochloric acid is mixed with milk of lime slurry with Ca(OH)2 content in the range between 5% and 35%, thereby neutralizing the hydrochloric acid and iron chlorides and forming a precipitate of iron hydroxide, the precipitate of iron hydroxide is oxidized with ambient oxygen for 5-40 hours, the slurry is cooled and filtered, the precipitate is washed and calcined at a temperature of 350 to 1000° C. for 1-10 hours, after which a resulting red iron oxide pigment is obtained, the red iron oxide pigment resulting from calcination is cooled and subjected to milling, while at the same time an oxidizing agent is introduced into the mother liquor and which is then neutralized to a pH=7-12 with Ca(OH)2 to form a resulting mother liquor slurry, wherein the mother liquor slurry is filtered to separate the precipitated iron hydroxide from the mother liquor to result in an iron hydroxide cake, then the iron hydroxide cake is dissolved using hydrochloric acid solution, thus obtaining a solution of iron chloride FeCl3, with a pH in the range of 0.5-2.0, after which FeCl3 is reduced to FeCl2 using iron and the resulting solution of FeCl2 is sent for mixing with solutions supplied from Stage d), and the mother liquor is sent to Stage i) for processing;
• h) precipitation of iron hydroxides to obtain yellow iron oxide pigment, during which, for the production of nuclei, part of the mother liquor from Stage d) containing iron chlorides and free hydrochloric acid is mixed with milk of lime slurry having Ca(OH)2 content in the range between 5% and 35%, hydrochloric acid and iron chloride are neutralized and a resulting slurry is held for 0.1-2 hours with continuous circulation provided, then iron hydroxide is oxidized with ambient oxygen for 5-40 hours, followed by the addition of the rest of the mother liquor from Stage d), free hydrochloric acid, and iron chloride are neutralized and iron hydroxide is oxidized with ambient oxygen for 5-40 hours, the slurry is cooled and filtered, the iron hydroxide is washed and dried at a temperature of 30-80° C., after which the resulting yellow iron oxide pigment is subjected to milling, while at the same time an oxidizing agent is introduced into the mother liquor from the stage of precipitate washing and the solution is neutralized to a pH=7-12 with Ca(OH)2 and the resulting slurry is filtered to separate the precipitated iron hydroxide from the mother liquor to result in an iron hydroxide cake, then the iron hydroxide cake is dissolved using hydrochloric acid solution, thus obtaining a solution of iron chloride FeCl3, with a pH in the range of 0.5-2.0, after which FeCl3 is reduced to FeCl2 using iron and the resulting solution of iron (II) chloride is sent for mixing with solutions supplied from Stage d), and the mother liquor is sent to Stage i) for processing;
• i) processing mother liquor containing calcium chloride, during which the mother liquors from Stages f), g), h) are used, calcium carbonate is precipitated using ammonia or ammonium compounds and carbon oxide or carbonates, the calcium carbonate precipitate is washed, filtered and dried at a temperature of 100-200° C., while the resulting mother liquor is sent to Stage j);
• j) regeneration of hydrogen chloride from ammonium chloride solution, during which the mother liquor from Stage i) is evaporated to a concentration of NH4Cl≤773 g/dm3, then, with thorough stirring, 95-100% sulfuric acid is fed according to a ratio of NH4Cl to H2SO4 of 1-1.75-2.05 to produce a reaction mass, then the reaction mass is heated to a temperature of 100-220° C. at an absolute pressure in the range of 0.15-1 bar, wherein hydrochloric acid released as a result of the reaction, having an HCl content of 10-35%, is condensed and returned to Stage a) of titanium-containing feedstock digestion, and the reaction mass containing ammonium hydrogen sulfate NH4HSO4 is sent to Stage k);
• k) obtaining ammonium sulfate and ammonium sulfate crystals by crystallization, during which the reaction mass obtained in Stage j) containing ammonium hydrogen sulfate is dissolved with water until crystals of ammonium hydrogen sulfate are completely dissolved, and simultaneously heating the dissolved mixture, the resulting solution of ammonium hydrogen sulfate having an NH4HSO4 content of 45-70% is mixed with a stream of ammonia gas, then the resulting ammonium sulfate solution is evaporated at an absolute pressure of 0.05-1 bar and crystallized, and the resulting slurry containing ammonium sulfate crystals with a solid (NH4)2SO4 content in the range between 5 and 50%, wherein the resulting slurry is further processed to separate the mother liquor using filtration or centrifugation, and wherein the separated ammonium sulfate crystals are washed and dried to remove free moisture at a temperature of 50-150° C., while the resulting mother liquor is returned to any one of stages a-k.