| Chromite ore, one of the basic industrial materials and one of the most competitive in the eight kinds of resource materials, plays an important role in everyday life. At present, the high-toxic chromium containing residue and Cr6+containing CO2green house gas from conventional chromate production process had brought serious environmental problems and made the chromic salt industry embarrassed. Institute of Process Engineering, Chinese Academy of Sciences had recently proposed and developed a novel cleaner chromate manufacturing process (sub-molten salt process). In this process, besides the reaction temperature decreased significantly to320℃, the chromite utilization efficiency had been sharply improved beyond99%, and emission of chromium containing residue approaching zero compared with traditional one. Based on the novel sub-molten salt process from the peer researchers, the influence of impurities in chromite ore on the chromium conversion rate of sub-molten salt reaction was analyzed. And high temperature roasting pro-treating chromite ore can strengthen oxygen enriched roasting and sub-molten salt reaction, in order to further optimize the existing chromite production process and reduce energy consumption significantly. The research results were summarized as followed:(1) The sub-molten salt reaction of Xinjiang ore and Indian ore with potassium hydroxide was studied. The process conditions were determined:the mass ratio of alkali-to-ore was5:1, reaction temperature was340℃, stirring rate was800r/min, and air flow was200L/h, reacted for6h. The converting rate of chromium tended to99.5%and the chromium content was lower than0.2%. Results showed that the ingredients of chromite ore influenced the chromium conversion rate in sub-molten salt reactions of different chromite ore and potassium hydroxide. Different ingredients content showed that Fe2O3slightly affected the chromium conversion rate in the process of reactions, because beneficiation of Fe2O3was in the slag. The conversion of Al2O3into potassium aluminate and the complex silicate generated by SiO2reduced the chromium conversion rate, respectively, because their products affected the viscosity of the liquid. (2) The influence of strengthen on no calcium roasting through oxygen was researched. Results showed that rich oxygen had a promoting effect on the chromium conversion rate during the process of no calcium roasting. Under the same condition, the chromium conversion rate increased by16%when oxygen content was from20%to100%. When ore:slag:alkali was100:100:150, calcinations temperature was1150℃, reaction time was2h, oxygen content was more than80%, the chromium conversion rate reached more than95%.(3) The liquid-solid separation process of chromite oxygen-enriched roasting clinker was invested. The conditions were determined:leaching temperature was100℃, leaching time was25min,l/s was5:1and the particle of clinker was38～74um. Due to the water soluble of Al, the leaching rate of Al tended to100%and the aluminosilicate was coagulated which was better for filtration.(4) The influence of crystal structure variation of chromite ore in the process of pre-roasting and the law of sub-molten salt reaction after the chromite ore in advance was studied. The results showed that, at the temperature above700℃, the exposing of Cr2O3was from chromite ore due to the damage of the spinel structure after preroasting. Under the optimum conditions alkali-ore (4:1), reaction temperature (300℃), reaction time (2h), the chromium conversion rate reached more than99%, which was far superior to the condition of existing production process of sub-molten salt chromium salt. |
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