Study On Sulfur Removal In The Process Of Producing Alumina From High-sulfur Bauxit

The sulfur in high-sulfur bauxite enters the sodium aluminate solution in the form of sulfur of different valence states(S^2-,S₂O₃^2-,SO₃^2-,SO₄^2-)during the dissolution process,causing many hazards to industrial production of alumina.Therefore,studying an economically feasible method to reduce the sulfur in high-sulfur bauxite to meet the production requirements of Bayer method has important practical significance for the effective utilization of high-sulfur bauxite in China.In this paper,taking the high sulfur bauxite of an aluminum oxide plant in Guizhou as the research object,thermodynamic calculation and theoretical analysis were carried out on the dissolution of different valence sulfur in the high sulfur bauxite and the oxidation of low sulfur by different oxidants.Through the study of the dissolution experiment of high sulfur bauxite under different experimental conditions,the sulfur dissolution behavior of high sulfur bauxite is clarified.Through wet oxidation desulfurization experiment,the oxidation capacity of different oxidants to low sulfur in solution was analyzed and compared,and the optimal oxidation conditions and oxidation effects of different oxidants were determined.On the basis of wet oxidation desulfurization with oxidant,copper oxide was selected as the catalyst for the experiment of catalytic oxidation desulfurization,and the catalytic oxidation effects of different catalytic conditions on different valence sulfur in sodium aluminate solution were studied respectively.The main results of this paper are as follows;（1）The study of sulfur removal by pretreatment and oxidation of high-sulfur bauxite was carried out.First,the effects of different experimental conditions on the total sulfur content and sulfur dissolution rate in the alkaline liquor were studied.The results show that the best dissolution conditions are dissolution temperature 90℃,dissolution time 60 min,alkali concentration 220g/L,the total sulfur content at this time is 4.32g/L,and the sulfur dissolution rate is 26.73%.（2）Theoretical calculations show that in the temperature range of 100～400℃,the easy order of sulfur generation in different valence states is S^2->SO₄^2->SO₃^2->S₂O₃^2->S₂^2->S.Based on the oxidation of S^2-to SO₄^2-,the oxidation capacity of the four oxidants is KMn O₄>H₂O₂>O₂>Na NO₃.Finally,the kinetics of oxygen wet oxidative desulfurization were studied.The kinetic rate expression of oxygen wet oxidation of S^2-can be expressed by the equation-（?）,and the activation energy Ea=2.73KJ·mol is obtained.The results show that the reaction rate of oxygen oxidation of S^2-follows the first-order reaction relationship with the S_2-concentration in solution.（3）Different experimental conditions affect the dissolution behavior of sulfur,alumina dissolution rate and sulfur dissolution rate in high-sulfur bauxite.The best dissolution conditions of high-sulfur bauxite are:Ca O addition amount of 13%,dissolution temperature 260°C,dissolution time 60min,alkali concentration 250g/L,alumina dissolution rate 86.77%,sulfur dissolution rate 34.56%.（4）The experimental results show that the four oxidants can oxidize S^2-in solution and increase the content of SO₄^2-in solution.The addition amount of H₂O₂is 9%,the oxidation temperature is 260℃,the oxidation time is 60min,and the removal efficiency of S^2-oxidation in the solution is 91.85%;The addition amount of sodium nitrate is 3%,the oxidation time is 80min,the oxidation temperature is 260℃,and the S^2-removal efficiency is 67.26%;The addition amount of KMn O₄is 4%,the oxidation temperature is 260℃,and the oxidation time is 60min.At this time,the S^2-removal efficiency is 57.64%.Under the conditions of oxygen input 10.25g/L,oxidation time 60min,oxidation temperature 260℃,S^2-oxidation removal efficiency is 99.13%（5）On the basis of the best experimental conditions of oxygen oxidation desulfurization,the catalytic oxidation desulfurization was studied.The results show that Cu O as a catalyst can almost completely oxidize S^2-in the solution,and the oxidation removal rate for difficult to oxidize S₂O₃^2-is 23.62%,while the SO₃^2-removal rate is 74.27%.