Study On Phosphate Removal By Superconducting Magnetic Separation Combined With FeOOH

Phosphorous is the main cause of water eutrophication,but it is also an important mineral resource.Therefore,it is of great practical significance to study on the recovery of phosphorous from wastewater.The current water treatment processes emphasize on phosphorous removal,and ignore the recovery of phosphorous,which result in an increasing amount of sludge.Combined with superconducting magnetic separation,this paper proposed the use of iron oxyhydroxide magnetic adsorbents for phosphorus removal and recovery process.Three FeOOH adsorbents with mean particle size of 36.47μm,40.74μm,58.68μm（T1,T2,T3）were prepared through a method of co-precipitation followed by screening.XRD analysis showed that the FeOOH was an amorphous structure.Particle size was an effect on saturated adsorption capacity.Finer particles showed larger adsorption capacity.Aqueous phosphate concentration decreased as FeOOH dosages increased.In order to obtain a concentration lower than 0.5mg/L,a dosage of 2g/L and 4g/L FeOOH was needed when the initial phosphorous concentration was 2mg/l and 5 mg/L,respectively.The size of FeOOH had effects on magnetic separation.Large particles were advantageous to the capturing of FeOOH in the magnetic field.A number of 1087 column volumes were reached with T1 used in the breakthrough test.The P concentration of effluent was lower than 0.5mg/L in the magnetic separation,and the removal rate reached up to 92.5%.NaOH was used as the desorption solution.The relative optimal NaOH concentration was 1.5 mol/L and the desorption rate of phosphate was 98.57%.CaCl2 was added into the desorption solution to recover phosphorous.The phosphorous recovery rate was 91.23% when the rate between n（Ca）and n（P）was 6.68.The concentration of phosphate in the product reached 40.03%（calculated by P2O5）.Based on the above,four Fe₃O₄@FeOOH adsorbents（H1-H4）were prepared through coating Fe₃O₄ by FeOOH of different rates.The intensity of Fe₃O₄ peak in XRD decreased as Fe₃O₄ rate in the adsorbents decreased.FTIR spectra showed that the-OH group of the adsorbents decreased with the increase of Fe₃O₄ rate.Adsorbents with Fe₃O₄ showed ferromagnetism,and H4 showed a higher magnetization than the other three adsorbents.With the increase of the rate of Fe₃O₄ in the adsorbents,the adsorption capacity of the adsorbents decreased from 11.67mg/g to 4.55mg/g,and the adsorption of phosphorus was inhibited by wastewater.In order to obtain a concentration lower than 0.5mg/L,2g/L of H1,3g/L of H2,3.5g/L H3 and 4g/L H4 was needed.Under the premise of ensuring that the effluent concentration was lower than 0.5mg/L,the H1-H4 adsorbent could be repeatedly adsorbed for 4,3,2,and 1 times,respectively.A higher magnetization and lower flow velocity were advantageous to the capturing of FeOOH in the magnetic field.The desorption rate of the four adsorbents was similar to each other,and were all reached more than 98%.The main component of the products was HAP,and the phosphorus content was 38.25%（calculated by P2O5）,and the recovery rate was above 90%.The processing capacity and cost of the 600 mm bore industry-scale superconducting magnetic separator are evaluated.The processing capacity and cost of superconducting magnetic separation are 6.86×106 t/a and 2.44 yuan/t,respectively.