Modified Sodium Alginate Composite\Compound With Coagulant On Treating AgNPs And The Feasibility Of Flocs Regeneration

With the wide application of nanomaterials,the potential harm of nanoparticles to the environment and ecology has attracted the attention of researchers.Coagulation-ultrafiltration（C-UF）process is considered to be one of the highly efficient processes for controlling the contamination of nanopaticles.Aiming at the limitation of traditional coagulants which can not remove the nanopaticles efficiently and the low efficiency of inhibition for membrane fouling,this study grafted AM,DMDAAC to SA by free radical reaction and named MSA.The removal efficeincy of silver nanoparticles（AgNPs）and inhibition for membrane fouling under different conditions（dosage and initial pH）were investigated when the MSA was used in combination with polyaluminum chloride（PAC）and titanium tetrachloride（TiCl₄）treating the AgNPs water sample.In addition,the effect of AgNPs on sludge disposal and reuse of titanium salt was also studied.The main research contents and conclusions are as follows:1.In order to clear out the optimum modification conditins,the MSA was used in the treatment of humic acid-kaolin water sample.According to the coagulationefficiency,the optimum conditions were as follows:the mass of SA was 1g,the initiator concentration was 6 mmol/L,the mass ratio of SA,AM and DMDAAC was 1:2:1.8,the reaction temperature was 45℃ and the reation time was 4 h.The FTIR,SEM,TEM and other data showed that the MSA was a high molecular weight subsatances,which has the rough surface and thick water-soluble form.And its surface charge was close to the isoelectric point due to the grafting of the amine group.2.MSA with positive group and long chain structure can be combined with PAC forming PAC-MSA composite coagulant,which can improve the coagution efficiency of PAC and the optimum compound ratio（PAC/MSA）was 1:0.25.Compared with PAC alone and PAC+SA compound coagulant,PAC-MSA has a better coagulation effect.Under the optimum dosage of 8 mg/L（calculate as Al）,PAC-MSA can remove more than 90%AgNPs and the removal efficiency of DOC increased 25%.In addition,PAC-MSA can produce larger and more loose flocs especially in the high dosage and acidic conditions.This character allowed the PAC-MSA resulting in the minimal membrane resistance,which was reduced by a maximum of about 37%compared with PAC and caused the membrane to lightest contamination.3.MSA as a coagulant aid used with TiCl₄ forming TiCl₄+MSA compound coagulant,which can be more effective in the removal of AgNPs on the basis of TiCl₄ and TiCl₄+SA,especially at the low TiCl₄ dosage.Under the optimum conditions（TiCl₄=12.0 mg/L,MSA=1.0 mg/L）,TiCl₄-MSA can remove more than 90%AgNPs.Besides,the pH of solution has a certain effect on the coagulation effect of TiCl₄ + MSA,and the acidic condition is more favorable for its coagulation.TiCl₄ + MSA can produce larger and more loose floc,floc size can be increased by 300μm compared with PAC.And the particle size distribution of the particles in the three coagulants increased with the increase of dosage and pH.In comparison,TiCl₄+MSA coagulated water contained more particles with larger particle size,which all had the effect on the following membrane fouling.The cake layer foemed by TiCl₄+MSA was loose and porous,which greatly inhibited the subsequent formation of ultrafiltration membrane fouling.While TiCl₄+SA formed a dense cake layer,which aggravated the membrane fouling.By analyzing the existence of silver elements in the flocs,it was found that TiCl₄+MSA could not only adsorb in the form of elemental silver,but also the silver ions dissociated from AgNPs.This would significantly reduce the toxicity of AgNPs in the water environment.4.Based on the research of the properties of AgNPs floc calcined products,the study discussed the feasibility of the regeneration of AgNPs flocs and clarified the effect of MSA on floc regeneration.The results indicated that the presence of AgNPs did not affect the regeneration of TiCl₄ floc for anatase TiO₂ and its photocatalytic performance is increased by 30%due to silver doping.Besides the floc products regenerated by TiCl₄+MSA contain more anatase TiO₂,and its photocatalytic performance increased by 20%compared with PAC flocs.While the photocatalytic performance of TiCl₄+SA flocs was reduced.This proved the regeneration feasibility of AgNPs flocs.