Reverse Osmosis Membrane Treatment And Recycling Utilization Of Waste Water Of FePO₄

Industrial wastewater has always been the main source of water pollution.With the continuous improvement of people’s environmental awareness,the industrial wastewater discharge standard are getting stricter,and new challenges to wastewater treatment technology are put forward.Recycling and zero discharge of industrial wastewater to achieve green production has become the future development direction and goal of industrial production.Traditional treatment methods of industrial wastewater mainly include precipitation method,adsorption method,biological method,evaporation and concentration technology,etc.,but these methods are difficult to meet the requirements of recycling and zero discharge.In recent decades,with the continuous development of new energy storage materials,mobile energy storage technology and electric vehicles,the demand for lithium iron phosphate cathode materials has increased sharply.Iron phosphate is one of the most important raw materials for the production of lithium iron phosphate,so the market demand for iron phosphate is also very strong.The raw materials for the production of battery grade iron phosphate are mainly ferric nitrate,ferric chloride and ferric sulfate.In order to reduce the production cost,ferrous sulfate,a by-product produced during the production of titanium dioxide,has also become an important raw material for the production of iron phosphate.In the process of producing iron phosphate from ferrous sulfate,a large amount of waste water containing sulfuric acid,phosphate,sodium ions and other impurities will be produced,and direct discharge will cause serious environmental pollution.In order to reduce waste water discharge and recycle waste water,the reverse osmosis technology was used to design a zero-discharge process for producing battery grade iron phosphate,and CaSO₄ whisker and Fe PO₄ were prepared by mixing filtrate and concentrated liquid.The effects of operating pressure,liquid concentration,temperature and p H value on the retention rate of sulfate and phosphate,membrane flux and water yield during membrane separation were investigated.The effects of different concentration of liquid solution,reaction temperature and concentration of controlling agent on the morphology and aspect ratio of CaSO₄ whiskers were studied.The prepared CaSO₄ whiskers were also characterized by SEM,XRD and TG.The CaSO₄whisker was used as the filling material to prepare the CaSO₄ whisker/PVC composite,and the influence of different CaSO₄ whisker filling amount on the mechanical properties of the composite was studied.Meanwhile,the antirust property of prepared Fe PO₄ was also investigated.The main results are as follows:1.The reverse osmosis membrane has a high retention rate of over 99.2%for both SO₄^2-and PO₄^3-.The operating pressure,liquid concentration and temperature had a significant influence on the membrane flux and water yield,while the p H value had little influence on the membrane flux and water yield.The optimum process conditions were determined as:inlet pressure is 0.6 MPa,concentration of SO₄^2-and PO₄^3-in wastewater are 0.01-0.02 mol·L^-1,temperature is 25-30℃,p H is 6-8.2.CaSO₄ whiskers can be prepared at mass concentration range of 0.1～1.0%of morphology control agent R,its width is about 1-5μm and aspect ratio is 20-30.The optimum preparation conditions were as follows:SO₄^2-contentration is 0.3mol/L,reaction temperature is 80℃.3.The mechanical properties of CaSO₄ whisker/PVC composite can be significantly improved compared with the PVC material.Compared with the Ca CO₃/PVC composite filled with the same amount,the results showed that the impact strength of CaSO₄ whisker was similar to that of the Ca CO₃ composite,and the tensile strength,elongation at break and bending modulus of calcium sulfate whisker/PVC composite increased by 46.8%,40.6%and 50.3%respectively compared with PVC,and the increase percentage was better than that of calcium carbonate.4.The antirust performance of prepared Fe SO₄ is slightly worse than that of aluminum tripolyphosphate,but it still shows good antirust performance.