Study On Recovery Of Magnesium Sulfate By Oxidation Of Magnesium Sulfate In Desulfurization Wastewater

Magnesium desulfurization process is one of the most widely used coal desulfurization technologies in China at present.It is the key to the sustainable development of magnesium desulfurization process to efficiently oxidize its by-product magnesium sulfite into magnesium sulfate for recycling.In order to improve the oxidation rate and efficiency of magnesium sulfate from magnesium sulfite,a product of magnesium desulfurization,this paper studies the influencing factors of oxidation rate and efficiency of magnesium sulfate from magnesium sulfite under the optimal catalytic system of manganese dioxide and ultraviolet light through the selection of catalytic system,and discusses the mechanism of free radical oxidation.The results are as follows.1.Through the research on the influencing factors of oxidation rate and oxidation efficiency of magnesium sulfite to magnesium sulfate under the condition of non-catalytic oxidation,it is determined that when the solution p H is 8,the aeration rate is 2 L·min^-1,the stirring speed is 1250 r·min^-1,and the temperature is 65℃,the oxidation rate and oxidation efficiency of magnesium sulfite to magnesium sulfate reach the maximum,which are 0.0219 mmol·L^-1·s^-1and 15.47%,respectively.2.Four catalytic oxidation systems of non-catalytic,ultraviolet irradiation,manganese dioxide and manganese dioxide combined with ultraviolet irradiation,were selected and studied.The results showed that the oxidation rate and oxidation efficiency of magnesium sulfite produced by different catalytic systems were as follows:manganese dioxide combined with ultraviolet irradiation>manganese dioxide>ultraviolet irradiation>non-catalysis,and the oxidation rate and oxidation efficiency were 0.0725 mmol·L^-1·s^-1and 47.01%respectively;0.0535 mmol·L^-1·s^-1and 39.24%;0.026 mmol·L^-1·s^-1and 18.72%;0.0135 mmol·L^-1·s^-1and 10.12%.3.Through the research on the influencing factors of oxidation rate and oxidation efficiency of magnesium sulfite to magnesium sulfate under the catalysis system of manganese dioxide and ultraviolet light,it is determined that when the dosage of manganese dioxide is 5.5 g·L^-1,the p H of the solution is 5,the aeration rate is 2L·min^-1,the stirring speed is 1250 r·min^-1,and the temperature is 65℃,the oxidation rate and oxidation efficiency of magnesium sulfate generated by magnesium sulfite reached the maximum value,0.0889 mmol·L^-1·s^-1and 71.32%,respectively.4.The oxidation rate of magnesium sulfite to magnesium sulfate under the optimal reaction condition of catalytic oxidation is more than 4 times that under the optimal reaction condition of non-catalytic oxidation,and the oxidation efficiency is more than4.6 times.Under the catalytic oxidation condition,the concentration and yield of magnesium sulfate from 20 g·L^-1magnesium sulfite were 17.12 g·L^-1and 85.6%,respectively,which were 4.6 times higher than those under the non-catalytic oxidation condition.5.The main reason for the best oxidation rate and oxidation efficiency of magnesium sulfite to magnesium sulfate under the catalytic conditions of manganese dioxide and ultraviolet light irradiation is that under the catalytic conditions,·OH,HO₂·,O·,·O₂^-,SO₄^-·,·SO₅^-and other free radicals are generated in the system,which accelerates the oxidation rate and oxidation efficiency of sulfite to sulfate.