Chromium Salts Calcium-free Roasting Process Vanadium, Chromium Enrichment Separation

With low resource utilization and calcium-containing chromium residue pollution problems in calcium roasting technology for chromium salt, the elimination of calcium roasting technology and promotion of clean producing technology such as non-calcium roasting technology is explicitly encouraged in chromium salt industry-wide. In this thesis, two issues are restricting the development of non-calcium roasting technology for chromium salt: resource utilization of chromium slag and removal of vanadium from sodium chromate leachate. The theoretical basis of the resource utilization of chromium slag is obtained through systematic analysis on chromium slag; preliminary enrichment and high leaching rate is achived by using acidic medium in the leaching process of chromium slag; a new non-calcium efficient and clean method to remove vanadium from sodium chromate leachate is established, which offers important theoretical basis and practical value for non-calcium roasting technology. Main innovative results obtained in this paper are as follows:1) The phase structure and composition of chromium slag is determined by systematic analysis and characterization.The main components are:chromite (FeCr2O4), iron magnesium (Mg (Fe, Al)2O4), the kind of spinel’s content is73.11%; hematite (a-iron)12.42%; sodium nepheline(NaAlSiO4)10.02%; free state of periclase (MgO)0.38%; calcined intermediate silica and calcite are2.17%and1.75%, respectively; unknown ash0.15%.2) Optimum condition for sulfuric acid enrichment of chrome spinel phase in chromium slag at low temperatures is obtained. It is found that chromite is severely parceled by aluminosilicate in the slag phase study. According to that, sulfuric acid is used to decompose aluminosilicate to make chromium component enriched. The effect of acid concentration, reaction temperature and reaction time on acid chemical enrichment of chromium slag is studied. Chromium content in chromium slag increased from16.44%to22.10%, iron from31.16%increased to39.54%, the slag after the enrichment can be back to the process as a secondary non-calcium roasting slag.3) New technology of leaching Chromium in chromium slag is developed. Through systematic study of sulfuric acid concentration, reaction temperature, the amount of chromic anhydride added, reaction time, size and other factors on chromium, optimum condition for dissolution on chromium in chromium slag has been obtained, the dissolution rate can reach 97.93%, efficient conversion of chromium in slag is achieved. The dissolution slag is silica-based, with80.8%SiO2, which could be used as a primary material in making glass to be utilized in the subsequent process.4) A new non-calcium method to remove vanadium from sodium chromate leachate is formed. In connection with the existing problems of calcium added capacity, the need to repeatedly adjust the pH value, large amount of the vanadium slag with hexavalent chromium, difficult to be used and other issues, it is intended to use iron as vanadium vanadium precipitation. The effects of added amount of iron salt, pH value and temperature on the rate of vanadium removal is studied to obtain the optimum process condition, the vanadium removal rate is95%or more, satisfing the requirement of the subsequent process.The characterization of slag phase shows that the adsorption mechanism is adsorption the vanadate on the inner surface of ferric hydroxide.