Study On The Leaching Behavior Of Titanium Slag In Ammonium-fluoride System

The preparation of titanium dioxide by fluorination method can realize the circulation of reagents,and is expected to replace the production process of titanium dioxide by sulfuric acid method with serious environmental pollution.It is a clean new method of titanium dioxide production.The leaching process of this method determines the titanium recovery rate and the quality of titanium dioxide products.It is of great significance to find out the dissolution behavior of titanium and impurity elements during the leaching process,which is of great significance for promoting the engineering application of the new method.Taking titanium slag as the object,the research on the reaction process and microscopic evolution behavior of fluorination leaching was carried out,and the following main conclusions were obtained:（1）During the leaching process of titanium-containing minerals and main gangue minerals,H⁺in the ammonium fluoride system first dissolves titanium and impurity elements,and then combines with other ions in the ammonium fluoride system to form corresponding compounds.The rutile leaching reaction requires the highest H⁺concentration,and the reaction can only occur when the[NH₄⁺]/[F^-]is 0,that is,the hydrofluoric acid system.Titanium-containing minerals such as iron brookite,magnesium brookite,aluminum brookite,titanium pentoxide and ilmenite have lower H⁺concentration requirements than rutile,and the reaction can occur when the[NH₄⁺]/[F^-]is less than 1,calcium silicate can react at any[NH₄⁺]/[F^-].In addition to calcium and magnesium ions to form Ca F₂and Mg F₂ precipitation,titanium and other component ions generate corresponding fluorine（oxy）ammonium titanate and fluorine ammonium salt complexes respectively with the increase of[NH₄⁺]/[F^-].Among them,the saturated solubility of ammonium fluoride（oxy）ammonium titanate and ammonium fluorosilicate is obviously higher than that of other component ion ammonium fluoride complexes.（2）During the leaching process of titanium slag,the titanium ions dissolved by H⁺generate（NH₄）₂Ti F₆ into the solution,and calcium and magnesium ions will form Ca F₂ and Mg F₂ precipitation alone,and interact with some aluminum ions to form Ca Mg₂Al₂F₁₂,NH₄Mg Al F₆precipitation,and the rest of aluminum ions and iron ions form the corresponding（NH₄）₃Al F₆,（NH₄）₃Fe F₆ precipitates.With the increase of[NH₄⁺]/[F^-]in the leaching system,the reactivity of titanium slag decreased,and the selectivity of titanium and impurity elements was enhanced.When the[NH₄⁺]/[F^-]of the ammonium fluoride system is 0and 0.2,relatively dense product deposit layer is formed during the reaction process,when the[NH₄⁺]/[F^-]is 0.5,the structure of the product deposition layer formed in the reaction process is loose.（3）When titanium slag is used as the raw material for the preparation of titanium dioxide by the fluorination method,in order to achieve efficient dissolution of the Ti element,most of the impurity elements are precipitated,and to prevent the solid-phase products from forming a dense sedimentary layer that hinders the leaching reaction,it is recommended that the[NH₄⁺]/[F^-]control of the actual system be 0.5.The paper includes 105 figures,12 tables,and 90 references.