Study On Leaching Of Magnesium From Phosphorus Tailings By Simulated SO₂ Flue Gas

At present,the utilization rate of phosphate tailings is low,tailings accumulation can result in waste of resources and environmental pollution.In the situation that the phosphate ore resources is gradually depleted,these phosphate tailings should be available secondary resources.Therefore,it is an urgent need for the sustainable development of economy and resources to carry out the research on the utilization of phosphate tailings.Extracting elements in tailings by acidolysis is a kind of resource utilization method with development prospect.After analyzing various acid leaching methods,it was found that SO₂ can be removed while extracting metal elements from minerals,which has certain advantages.In this study,simulated SO₂flue gas was used as extractant,and its extraction performance of magnesium element in phosphate tailings was investigated by orthogonal experiment and single factor influence experiment.On the basis of single factor experiment,the kinetic process of the reaction system was analyzed,and the strengthening way of magnesium leaching was explored to shorten the reaction period.In the single factor experiment,the effects of reaction temperature,SO₂concentration in flue gas,solid-liquid ratio,p H and gas flow rate on the leaching rate were investigated.The results showed that the leaching rate increased with the increase of temperature,gas flow rate and the concentration of SO₂,but the solubility of SO₂ decreases with the increase of temperature,so the leaching rate is not sensitive to the change of temperature.The solid-liquid ratio had the greatest effect on the leaching rate,when the solid-liquid ratio increased,the leaching rate decreased rapidly.With the decrease of p H,the leaching rate increased,when the p H was 4,the leaching rate was the highest,and then the p H decreased,the leaching rate decreased.The results of orthogonal experiment showed that the order of effection was:solid-liquid ratio>gas flow rate>reaction temperature>p H>SO₂ concentration.The optimum reaction conditions were determined:solid-liquid ratio 1%,p H 5,gas flow rate600m L/min,SO₂ concentration 8500mg/m³,and reaction temperature 50℃,under which the leaching rate of magnesium could reach 97.74%after 120 min of reaction.The kinetic study was investigated by analyzing the main reaction steps of SO2flue gas extraction of phosphate tailings,which is simplified as the gas-liquid mass transfer process of sulfur dioxide dissolving and the solid-liquid mass transfer process of acid decomposing phosphorus tailing.Then,the internal control factor of the whole reaction system was obtained by discriminating the control steps of each stage.In the process of gas-liquid mass transfer,the gas film resistance and liquid film resistance are distinguished.Through the experiment of the influence of stirring speed on the leaching rate,it was concluded that the influence of gas-liquid film resistance can be ignored in this study.In the solid-liquid phase mass transfer process,three models were used to fit the relationship between leaching rate and reaction time at different reaction temperatures,and the fitting degree of the chemical reaction control model was the best.Then the experimental data under different reaction conditions were used to verify that the reaction system belongs to chemical reaction control.The activation energy of the reaction is 12.64 k J/mol,and the macro kinetic equation is1-2/3X-（1-X）²/3=0.4719?Q^0.899?e^-12640/RT?t.The results of strengthening experiments showed that calcination can effectively improve the leaching rate of magnesium.After calcination at 700℃for 2 hours,the surface structure of phosphate tailings became loose,and the porosity increased.The leaching rate of magnesium element increased by 49.91%,which effectively shortens the reaction period of the system.The enhancement effect of microwave treatment on the leaching rate was not obvious,the surface structure of phosphate tailings after microwave treatment changed little,.Therefore,microwave treatment could not effectively enhance the leaching rate of magnesium.The additive has certain strengthening effect on the leaching rate of magnesium,but the effect is small,among the adipic acid,citric acid,sodium citrate and sodium chloride,the strengthening effect of adipic acid was the best,sodium citrate was the lowest.