Abstract
During Bayer alumina production with high-sulfur bauxite, the sulfide ions in the sodium aluminate solution caused serious corrosion to Q235 steel, which is the material of the tank equipment. This study investigates the effect of corrosion time on Q235 steel synergistic corrosion in sodium aluminate solution using the weight-loss method and electrochemical measurements. The results indicate that the corrosion rate decreases sharply, the rate equation satisfies the mathematical model of power function at the initial stage of corrosion, and the transformation of unstable iron sulfide to stable iron oxide at the later stage results in the decrease in sulfur content in the corrosion products and surface pseudo-passivation. There are two main types of corrosion products, as follows: one is the octahedral crystal particle, which is composed of Fe2O3, Fe3O4, Al2O3 and NaFeO2, and the other is the interlayer corrosion between the surface layer and the matrix, which is composed of FeS, FeS2 and MnS2. At day 3, the dynamics of the Q235 steel electrode is controlled by charge transfer and ion diffusion. However, at other times the dynamics are mainly controlled by charge transfer.
Highlights
High-sulfur bauxite is a general term for bauxite with a sulfur content greater than0.7% [1]
(1) AtAtthe theinitial initialstage stageofofcorrosion, corrosion,the thecorrosion corrosionrate ratedecreases decreasessharply sharplyand andsatisfies satisfies the mathematical model of the power function, and iron sulfide with an unstable the mathematical model of the power function, and iron sulfide with an unstable structure is preferentially generated on the surface
(2) The corrosion products have two morphological patterns, as follows: one is the ococtahedral crystal particle, which is composed of Fe O, Fe O, Al2 O3 and NaFeO2, tahedral crystal particle, which is composed of Fe2O3,2Fe33O4, 3Al24O3 and
Summary
High-sulfur bauxite is a general term for bauxite with a sulfur content greater than. Are mainly formed by FeS2 reacting with alkali liquor during the high-pressure leaching process [7] These ionic forms of sulfur are prone to valence reactions and are called “active sulfur”, which can cause the corrosion of equipment material and other hazards to alumina production [8,9]. The influence of several kinds of sulfur, co-existing in the sodium aluminate solution, on the corrosion behavior of steel was studied by an author in 2018 [14], and the results showed that there is a certain synergistic effect among several sulfur forms. The main purpose is to systematically investigate the influence of corrosion time on the corrosion behavior of Q235 steel, and this will provide a theoretical basis for the material protection of alumina production equipment
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