Preparation Of Ferrous Sulfate From NdFeB Secondary Waste And Its Application Of Phosphorus Removal From Wastewater

With the expansion of NdFeB magnetic material application field,the demand increases,which also produces NdFeB magnetic material waste problem,waste recycling has become an important topic.However,the current research focuses on the recovery and utilization of rare earth and trace precious metals in the waste,ignoring the comprehensive utilization of the secondary waste generated after the recovery of rare earth,which not only causes the waste of resources,but also causes environmental pollution.In this paper,ferrous sulfate was prepared from secondary waste materials according to components and physical properties,and the application of ferrous sulfate in wastewater containing phosphorus was studied.The main research contents were as follows:(1)Experimental study on iron leaching rate.Considering the reasonable route of product preparation,sulfuric acid solution was used for leaching,the influencing factors of leaching temperature,acid concentration,acid hydrolysis time,liquid-solid ratio and leaching times were investigated experimentally.The experimental results showed that under the conditions of reaction temperature 90℃,sulfuric acid concentration 7.0 mol/L,acid leaching time 120 min,liquid-solid ratio 4:1 and leaching twice,the iron leaching rate reached 97.89%.Under these conditions,the two kinetic equations controlling the leaching process were fitted and analyzed.The correlation coefficient R2 of the curve fitting phase relationship value was greater than 0.90 to determine the controlling factors of the reaction rate in the leaching process,indicating that the leaching process was affected by chemical reaction control and diffusion control,and diffusion control was slightly dominant.(2)Reduction experimental study.The reduction temperature,reaction time and excess coefficient of scrap iron were experimentally studied.The optimum reduction conditions were as follows:under the conditions of temperature 80℃,excess coefficient of scrap iron 1.2,reaction time 120 min,The conversion rate of Fe3+ to Fe2+ reached 98.19%.(3)Study on extraction of ferrous sulfate by solution-crystallization.The solubility of ferrous sulfate in pure water and ethanol solution was measured,and the Apelbalt equation fitting was carried out,and the linear correlation coefficient was above 0.99.In the experiment,ferrous sulfate was extracted by dissolution method.The influence of initial concentration of ferrous sulfate,ethanol dosage,crystallization temperature and operating conditions on the crystallization rate was investigated.The experiment showed that when the solution temperature was 10℃,the concentration of ferrous sulfate solution was 200 g/L,the volume ratio of ethanol to ferrous sulfate solution was 1:1,the continuous dropping method was adopted for ethanol addition,the dropping acceleration was 10 mL/min,the stirring speed was 50 r·min-1,the aging time was 1 h,the crystallization rate was more than 95%.(4)Experimental study on phosphorus removal from wastewater by ferrous sulfate.When the temperature was 25℃ and the concentration of Fe2+,Fe3+ and PO43-was 1 mol/L,Using the Van ’t Hoff isothermal equation ΔrGm(T)=ΔrGmθ(T)+RTlnJ to computΔrGm(T,(Fe2+))and ΔrGm(T,(Fe3+)),the results were-56.86 KJ·mol-1 and-124.92 KJ·mol-1 respectively.This indicates that Fe2+ and Fe3+ are easy to form iron salt precipitation with phosphate to achieve the purpose of phosphorus removal.In this experiment,the simulated high phosphorus wastewater(containing phosphorus 100 mg/L)was taken as the research object.Through the investigation of the pH of the reaction system,the amount of hydrogen peroxide,Fe/P(molar ratio)and the oxidation mode,the results showed that the removal rate of phosphorus was above 97%with hydrogen peroxide concentration 7.23 mmol/L,Fe/P(molar ratio)1.6 and the reaction system pH=7.0.The removal of phosphorus from wastewater by ferrous sulfate is the result of three factors:the effect of unoxidized Fe2+on phosphate,the precipitation of newly oxidized Fe3+ on phosphate,and the adsorption and removal of phosphate by iron ion hydrolysate.The results showed that The results showed that Fe2+ alone had poor phosphorus removal effect,and the main product was Fe3(PO4)2.Under the condition of H2O2 oxidation,the removal product is mainly FePO4,accompanied by the adsorption of phosphorus by the hydrolysis product of iron ion.