Study On The Process For Chrome Ore Liquid Phase Oxidation And The Dissolution Equilibrium For Liquid Phase Oxidation System Of Chrome Ore

Chromate is one of the important basic raw materials in the chemical andmetalluraical, which accounted for70%of chromium salt production. The conventionalmanufacture method of chromium salts is the process of “calcium roasting of chromite”,Which has the disadvantages of low energy efficiency and high environmental pollution.Accordingly, it is gradually being replaced by the cleaner processes, e.g. calcium-freeroasting and liquid-phase oxidation. Among them, the liquid-phase oxidation processescan achieve high resource and energy efficiency and enable the comprehensiveutilization of the valuable components in chromite and zero emission of thechromium-containing residue, and therefore, have received considerable attentionduring the past decade.According to the characteristic of resources and the market demand in china, Anovel metallurgical clean process for production of chromate by decomposing chromitewith sub-molten salt was proposed in the present paper; meanwhile, the gold of thisresearch is to solve the following separation problem. As phase equilibrium is thefoundation of crystallization separation, this dissertation studied the separation methodof sodium chromate, sodium nitrate, sodium silicate in the sub-molten salt medium byusing stationary method to determine the solubility of the involved system, Which canprovide the theoretical basic for the process design and optimization of the sub-moltensalt technology.This paper mainly studies the following contents:（1）A reaction system of chromite and sub-molten NaOH was established. Thepossible products of main composition existed in residue were investigated in thedecomposition process with sub-molten NaOH. Effects of reaction temperature, times,oxidative pressure, NaOH-to-ore ratio and Alkali concentration on chromium extractionrate were studied. Approximately99%of chromium in the ore could be extraction underthe optimal reaction conditions, and using SEM showed that residue was Presence of asolid product layer,which characterized to be Iron oxide and magnesium compounds byXRD.（2）For the separation of Na2CrO4, NaAlO2andNa2SiO3in the sub-molten saltprocess, the solubility ofternary systems: NaOH–H2O–Na2CrO4, NaOH–H2O–NaAlO2;quaternary systems: NaOH–H2O–Na2CrO4–Na2SiO3, NaOH–H2O–Na2CrO4–NaAlO2 and NaOH–NaAlO2–Na2SiO3–H2O; quinary systems: NaOH–H2O–Na2CrO4–Na2SiO3–NaAlO2, was measured by using the equilibrium analysis method at the atmosphericpressure and temperature ranging from353.15K to403.15K. Except the Na2CrO4solubility in the NaOH–H2O–Na2CrO4ternary system, The result show that the decreaseof Na2CrO4solubility with an increase in NaOH concentration is very obvious.However, when NaOH concentration is larger than500g·L-1, the variation of Na2CrO4solubility with NaOH concentration becomes very small and increases with increasingtemperature; The solubility of NaAlO2also increases with increasing temperature, but itGreatly influenced by temperature.（3）The experimental data were correlated by the ideal equation, λ-h equation,and Apelblat equation, demonstrating the Apelblat equation can well predict thesolubility of the systems.（4）The results showed that the existence of NaAlO2and Na2SiO3leads to andecrease in Na2CrO4solubility, while the coexistence of NaAlO2and Na2SiO3has lesseffect on Na2CrO4solubility than the sole existence of NaAlO2and Na2SiO3.