Removal Of Fluorine And Phosphorus In Phosphoric Acid Wastewater By Neutralization,Flocculation And Adsorption Process

This paper was based on waste water including 515mg/L fluorinion and 958mg/L total phosphorus produced in production technology of phosphoric acid in Hubei Dajiang Chemical Group Co.Ltd.The existing processes including two-step neutralization,two-step flocculation and adsorption were improved by processes including neutralization by alkaline white mud,flocculation and adsorption by modified fly ash.The key point of the processes was that the alkaline white mud by ball mill beating was used in the stage of neutralization and that the fly ash modified by H₂SO₄ and Fe³⁺ was used in the stage of adsorption.Compare the improved processes with the existing processes,the effluent concentration of fluorinion was reduced from 12.6mg/L to 0.64mg/L,the effluent concentration of total phosphorus was reduced from 4.5mg/L to 1.3mg/L,the reactions time of neutralization and adsorption were reduced from 120 min to 90 min,average cost of wastewater treatment was reduced from 6.76 yuan per ton to 4.00 yuan per ton,and the unstable emission was replace by stable emission reaching the national standard.This paper mainly discussed the following points.In these cases that the slurry concentration was 30%,the ratio of ball-to-powder ratio was 9:1,the ball milling time was135 min,and the ball milling speed was 450r/min,the minimum partical size of alkaline white mud was 1.08 um.In these cases that the partical size was 1.08 um,the pH was 3,the dosage was 36mL/L,and the reaction time was 90 min,the removal rate of fluorinion was96.8%,the removal rate of total phosphorus was 77.6%.Compared existing and improved neutralization and flocculation,the improved process had the advantages of less dosage,shorter reaction time and better treatment effect.In these cases that the partical size was1.08 um,the pH was 3,the dosage was 36mL/L,and the reaction time was 90 min,the removal rate of fluorinion was 96.8%,and the removal rate of total phosphorus was 77.6%.In these cases that the concentration of sulfide acid was 1.5mol/L,the impregnation ratio of sulfide acid was 5:10,the concentration of ferric iron was 0.055mol/L,and the impregnation ratio of ferric iron was 7:20,specific surface area of fly ash was increased from 2.49m²/g to 12.26m²/g,and ferric content was increased from 3.45% to 6.82%.In these cases that specific surface area was 12.26m²/g,ferric content was 6.82%,dosage of adsorbent was 12g/L,and time of adsorbent was 90 min,the removal rate of fluorinion was94.7%,and the removal rate of total phosphorus was 97.1%.Compared with theunmodified fly ash,the modified fly ash had the advantages of less adsorbent amount,shorter adsorption time and larger adsorption capacity.