Study On Dephosphorization Of Converter Slag By Leaching And Removal Of Phosphorus From Leach Liquor

In the fifth Plenary Session of the 18 th CPC Central Committee,the concept of "innovation,harmony,green,open and sharing" was put forward.Green development has become the main melody of "13th Five-Year" in China.As the industry of high energy consumption and emissions,the steel industry is facing tremendous pressure on resources and the environment during the "13th Five-Year" plan.The steel slag is the inevitable by-product in the steelmaking process,and it is a large amount of solid waste in the iron and steel industry.In 2016,China's crude steel production had exceeded 800 million tons,and steel slag production was about 80 million tons,however,the utilization rate of steel slag was only 25~30%.The stockpiling of steel slag not only pollute the environment and waste of resources.Recycling of steel slag in iron and steel industry would bring out a problem of phosphorus enrichment in hot metal,which will do harm to steelmaking process.In order to explore a kind of clean and environmentally friendly steel slag dephosphorization method.In this study,converter slag from a domestic steel work was used as the research object,dephosphorization from the steel slag by leaching with C6H8O7-NaOH-HCl solution and phosphorus removal from dephosphorization leach liquor were studied.In the present paper,dephosphorization from steelmaking slag by leaching with solution composed of citric acid,sodium hydroxide,hydrochloric acid and ion-exchanged water was studied.Kinetic parameters including temperature,slag particle size and solution pH were optimized.The results showed that temperature has no obvious effect on dissolution of phosphorus.The dephosphorization rate increase with the decrease of slag particle size and pH value of solution.90.0 % of phosphorus can be dissolved in the solution while the corresponding leaching ratio of iron was only 30.0 % after 40 min at pH2.2,25 °C and 75~125 ?m particle sizes.In order to clarify the leaching mechanism and increase the leaching rate,the kinetics of leaching process was analyzed.Leaching kinetics of dephosphorization follows the unreacted shrinking core model with a rate controlling step by the solid diffusion layer and the corresponding apparent activation energy is 1.233 kJ mol-1.In order to recycle the leach liquor,static adsorption experiments were designed to investigate the phosphate adsorption performances with activated aluminum oxide.The influencing factors included the adsorption time,adsorbent dosage and size,initial concentration of phosphorus and the pH of the leach liquor.The results showed that the dosage of adsorbent was related to the initial concentration of phosphorus;the best pH value of the leach liquor was 6.3;The particle size of adsorbent had a great influence on the removal rate and adsorption capacity.When the particle size was less than 1.18 mm,the dephosphorization ratio and adsorption capacity increased with the increase of particle size.However,when the particle size was larger than 2mm,the dephosphorization ratio and adsorption capacity decreased with the increase of particle size.When the particle size of the adsorbent ranged between 1.18 and 2mm,the phosphorus removal rate of activated alumina was the best.The phosphorus removal rate was 88 % and the adsorption capacity was 0.72 mg/g under the optimum experimental conditions.Adsorption isotherm and adsorption kinetic behavior were analyzed.The Freundlich model can better describe the process of phosphorus adsorption on activated alumina than the Langmuir model,and the pseudo-second order kinetic model can better describe the adsorption kinetics of phosphate on activated alumina.The adsorption of phosphate ions by activated alumina was mainly chemical adsorption.