Study On Antimony (?) Removal Efficiency And Membrane Fouling During Combined Process Of Ballasted Flocculation And Ultrafiltration

In recent years,with the development of the antimony industry,China has become the world's largest producer of antimony.At the same time,the problem of surface water resources being polluted by antimony is severe.In aqueous environments,antimony usually exists in the form of positive trivalent and positive pentavalent,and Sb???has greater solubility,fluidity and toxicity than Sb?V?.In this paper,the simulated water sample of humic acid?HA?-Sb???composite pollution was treated by the combined process of ballasted flocculation and ultrafiltration.Then the treatment effect and membrane fouling of the combined process were analysed.The effects of coagulant dosage,coagulant aid dosage,pH value and micro-sand dosage on the treatment efficiency in the combined process were investigated,and the membrane fouling was analysed based on the evolution of floc morphology.The results showed that the optimum coagulation conditions for the flocculation-ultrafiltration process were PFS 30.0mg/L,PAM 0.3mg/L,pH=7.0,micro-sand 3.0g/L and turbidity removal rate at 99.24%,HA removal rate at 96.13%,residue antimony concentration after ultrafiltration at 4.26?g/L.Further research found that the HA removal effect was dissatisfactory when the PFS dosage was low.When the dosage was too high,the HA-PFS system would be re-stabilized,and the removal rate also decreased.The residue Sb???concentration in the flocculation and ultrafiltration effluent decreased with the increase of PFS dosage.PAM and micro-sand have no direct effect on the removal of Sb???.However,it will indirectly affect the Sb???removal by ballasted flocculation through the removal of suspended particles.The mechanism of hydrazine may be the adsorption coprecipitation of PFS and Sb???,which is then intercepted by ultrafiltration membrane.During the flocculation process,PAM promoted the formation of flocs by the adsorption of briquettes and micro-sand particles.The greater the amount was,the larger the average particle size of the flocs with looser structure would be,but the excessive addition of PAM reduced the flux of the ultrafiltration membrane and the irreversible pollution of the membrane;In the range of pH=4.0-9.0,the residual strontium concentration after ultrafiltration had little effect,and the residual strontium concentration after loading flocculation was mainly positively correlated with the supernatant turbidity;when the micro-sand dosage was low,the flocculating carrier medium was insufficient,causing poor effect of flocculation.And the floc average particle size came with smaller diameter,which was not conducive to the attenuation of the membrane flux.But when the micro-sand dosage was too much,the flocculation density would increase and the average floc size decreased.The reason might be that surplus micro-sand destroys mature flocs and reduces the average size of flocs.It may also be that when there are more micro-sand,the number of flocs would be large and the size would be small,which ultimately leads to a larger attenuation of membrane flux.The experiment also showed that the degree of membrane fouling was affected by the morphological characteristics of flocs.When the average floc size was large and the structure was loose,the ultrafiltration process was beneficial to form a loose cake layer with large porosity,which made the membrane flux.The attenuation was usually slow and the membrane was less irreversible.The ultrafiltration membrane was chemically cleaned with different types of cleaning agents such as acid,alkali and oxidant.The results show that the alkaline solution can remove the humic acid on the surface of the membrane,and effectively alleviate the irreversible pollution of the membrane.The recovery effect of various types of cleaning agents on membrane fouling was:NaOH>NaClO>citric acid>H ₂ O₂.