Study On The Application Of Gore Membrane In The Making Of High Purity Phosphoric Acid And Determination Of Its Property

Phosphoric acid is grouped as four kinds by its production method, that is agricultural grade, technical grade, food grade and semiconductor grade. High purity phosphoric acid means food grade, semiconductor grade and other high purity and high concentration phosphoric acid. At present the production of high purity phosphoric acid is one big developmental tendency from the beginning of hot-process phosphoric acid. Hot-process phosphoric acid contains a little impurities which are mainly Pb and very little Zn, Cu, Ni, Mn, Cr and Cd. Phosphoric acid can be purified through adding heavy metal removal reagent to form sedimentations and then filtrate to get rid of them.In this study, P2S5 was used as heavy metal removal reagent to react with technical grade phosphoric acid heated by water bath, beat up, filtrated by Gore membrane at the first time instead of the normally used filtration cloth.Through orthorhombic experiment, the effect abilities of six factors were studied; through single factor experiment, the effect laws of react time, react temperature, react pressure, dosage of P2S5, filtration times by Gore membrane and sedimentation time were determined; then Gore membrane's interception rate, filtration constant, condensation exponent of filtration cake, filtration resistance, etc. were determined and compared with 747# and 758# filtration cloths.These following conclusions were drawn on the basis of the experiments:(1) It is feasible to use Gore membrane instead of filtration cloth to purify phosphoric acid in the production of high purity phosphoric acid. This method can greatly improve the filtration efficiency and the filtration effect is much better than the traditional method, the Pb removal rate can reaches 86.9 % filtrating once by Gore membrane and the rate is 95.5% at the best technical conditions. Gore membrane can successfully filtrate most of the impurities by once, the filtration effect is good and the phosphoric acid is clear and transparent after filtration.(2) Considering the practical production , the best technical conditions are : reaction time 60min, reaction pressure 2 105Pa ,reaction temperature 80 C, dosage of P2S5 0.2%, sedimentation time48h , filtration times 2 by Goremembrane . At the conditions, the Pb removal rate can reach 95.5% and the quantity of heavy metals decline to 2.6ppm.(3) At the pressure of 16.38Kpa, 24.66KP, 32.90KPa, the filtration constants when filtrating phosphoric acid by Gore membrane are K=0.2521m2/s, 0.3719m2/s, 0.489Im2/s respectively . The characteristic constant of phosphoric acid is k=1.2502 10-5m4/(N.s), the condensation exponent of filtration cake is s=0.05. Gore membrane's medium constants are :e=1010s, qe= 0.1483 m3/m2. The filtration cake can be regarded as impressible cake.(4) The general resistance of gore membrane are mainly the filtration cake resistance RC, it means the resistance of gore membrane itself is small. So it is more suitable to use Gore membrane when filtrating some fine suspending.(5) The interception rate of Gore membrane is 93.3% at 16.38Kpa and filtrating for 275 seconds. This rate is much better than those of 747# and 758 # filtration cloths. This demonstrates Gore membrane has good interception effect to the impurities in the phosphoric acid...