Preparation Of Nano Fe C Composite By Carbothermal Reduction And Its Arsenic Removal Performance

Nano zero valent iron is a new type of environmental remediation material with unique adsorption,reduction and flocculation,which can be widely used in wastewater treatment,soil remediation and other fields.Nano zero valent iron loaded on carbon matrix to form nano iron carbon composite can effectively inhibit the agglomeration of nano zero valent iron,and form iron carbon micro electrolysis effect to promote the removal of pollutants.At present,the main preparation method of nano iron carbon composites is impregnation reduction method,but this method has some defects,such as complex preparation process,low load and weak iron carbon bonding strength.In this paper,a new preparation method of nano iron carbon composites based on carbothermal reduction was explored.On this basis,taking the high arsenic waste acid in copper smelting as the research object,the arsenic removal process was systematically studied by single factor experiment,response surface optimization,dynamic fitting and other methods,and the mechanism of arsenic removal process was analyzed.Using carbon black as carbon source,ferrous oxalate,ferric oxalate,ferrous carbonate and ferric hydroxide as iron source,the preparation conditions of nano iron carbon composites were studied by carbothermal reduction method,and the reaction mechanism was analyzed.The results show that: when carbon black and ferrous oxalate are used as reaction system,under the conditions of temperature 900 ?,iron carbon molar ratio 1:3.4,reduction time 60 min,the zero valent iron content of the prepared nano iron carbon composite is 64.33%,the average particle size is about 50 nm,the microstructure is carbon black particles loaded with nano iron clusters,which is porous.The test results show that its arsenic removal performance is excellent.Under the same experimental conditions,the other three kinds of carbon black ferric salt systems have some disadvantages,such as insufficient reduction,serious agglomeration and low arsenic removal activity.Nano iron carbon composite was used to treat high arsenic waste acid.The effects of solution p H,iron dosage,arsenic solution concentration and arsenic solution temperature on arsenic removal process were investigated.Based on the results of single factor experiment,response surface optimization experiment was carried out,and kinetics and adsorption isotherm experiments were carried out to investigate the arsenic removal characteristics.The results showed that when the solution p H was 1.7,the iron dosage was 11 g/L,the initial concentration of arsenic solution was 5 g/L,the reaction time was 210 min,and the arsenic solution temperature was 40 ?,the arsenic removal rate of nano iron carbon composite reached 99.77%;The results show that the quadratic polynomial regression model is accurate and reliable.The order of the influence of various factors on the arsenic removal process is: Iron dosage >solution p H > arsenic concentration > arsenic temperature.The interaction between iron dosage and arsenic concentration is significant;The results of adsorption isotherm show that the process of arsenic removal is monolayer adsorption,and the maximum adsorption capacity is 546.6 mg As/g Fe,in which mass transfer and internal diffusion are the control steps of the whole adsorption process.A two-stage arsenic removal method based on nano iron carbon composite is proposed.The first stage arsenic removal process aims to achieve arsenic enrichment in slag,and the second stage arsenic removal process aims to achieve sewage discharge standard.The arsenic removal mechanism is analyzed.When the molar ratio of iron to arsenic is 2:1,the removal rate is 99.83%,the adsorption capacity is668.4 mg As/g Fe,and the residual arsenic concentration is 8.5 mg/L;When the mass ratio of iron to arsenic reaches 50:1,the arsenic removal rate reaches 98.78%,and the residual arsenic concentration in the solution is reduced to 0.104 mg/L.It has reached the limit specified in the national integrated industrial wastewater discharge standard(GB26132-2010).The results show that the nano iron carbon adsorbs arsenic to the active sites of the surface oxide layer,and forms a more closely bound internal complex with it.Part of arsenic passes through the oxide layer and is reduced to its low valence state near the zero valent iron core,and then both of them are removed by coprecipitation,showing mainly adsorption and coprecipitation,The law of arsenic removal with reduction as a supplement.A large number of hydrogen ions in the strong acid system and iron carbon micro electrolysis effect accelerate the corrosion and exfoliation of the oxide layer on the surface of the nano iron carbon composite,continue to provide adsorption sites and expose the fresh zero valent iron,which improves the utilization efficiency of the material.