Abstract:

In ammonia flue gas desulphurization，it is very important to determine the effect of liquid phase impurities on the crystallization of （NH₄）₂SO₄.In this paper，the effects of Fe³⁺ and Al³⁺ on the crystal shape and particle size distribution of （NH₄）₂SO₄ were studied by SEM，XRD and particle size analysis，and the effect mechanism of Fe³⁺ and Al³⁺ on the crystallization of （NH₄）₂SO₄ was revealed by molecular dynamics simulation.The results showed that when the concentration of Fe³⁺ in （NH₄）₂SO₄ solution was less than 200 mg/L or the concentration of Al³⁺ was less than 400 mg/L，the crystallized crystals existed in a regular prismatic shape with average particle sizes of about 168 µm and 169 µm，respectively，the uniformity was relatively high.When the concentration of Fe³⁺ in （NH₄）₂SO₄ solution was higher than 200 mg/L or the concentration of Al³⁺ was higher than 400 mg/L and continues to increase，the crystal shape of （NH₄）₂SO₄ crystal changes to sheet，and the average particle size and uniformity of （NH₄）₂SO₄ crystal showed a decreasing trend.Compared with Al³⁺，the increase of Fe³⁺ concentration had a greater inhibitory effect on the crystallization of （NH₄）₂SO₄.The molecular dynamics simulation showed that the adsorption energy of Fe³⁺/Al³⁺ and （NH₄）₂SO₄ crystal （020） surface was more negative than that of （NH₄）₂SO₄ molecule and （NH₄）₂SO₄ crystal （020） surface，and （NH₄）₂SO₄ was easy to form sheet.With the increase of Fe³⁺/Al³⁺ concentration，the pH of （NH₄）₂SO₄ solution was decreased，the metastable zone of solution was narrowed，resulting in the decrease of supersaturation，and ultimately the crystal size.Therefore，the crystallization properties of （NH₄）₂SO₄ could be reasonably regulated by controlling the concentration of Fe³⁺ and Al³⁺.

Key words: ammonia desulfurization, ammonium sulfate crystallization, Fe³⁺, Al³⁺, effect mechanism, molecular simulation