Preparation And Characterisation Of Polyaluminum Chloride-chitosan Composite Coagulant

With the constant development of economy,water pollution is becoming more and more serious in our country,the quality of flocculation effluent is getting higher and higher,the traditional aluminum salt and ferric salt flocculants might cause secondary pollution problems,therefore,the development and research of new flocculant is the hot spot in the field of current water treatment.Both polyaluminium chloride(PAC)with different preparation temperatures or alkalinity(B value)and polyaluminum chloride-chitosan(PAC-CTS)composite flocculant with different content of chitosan(C value)were prepared using AlCl3·6H2O,NaOH and chitosan as the main raw materials in this paper.First of all,Al-Ferron timed spectrophotometric method,transmission electron microscopy(TEM),X ray diffraction(XRD)and infrared spectroscopy(FT-IR)were used to investigate the distribution of aluminum species,microstructure morphology,crystal structure and chemical bonding with different preparation temperature,B value and C value.At the same time the interaction between PAC and CTS in the composite flocculant was analyzed.Then flocculation experiments of Reactive Blue 19 and humic acid as raw water was studied to investigate the flocculation properties of PAC and PAC-CTS composite flocculant with factors including the pH value,flocculant dosage,turbidity and stirring speed.Finally,the flocculation mechanism of two kinds of flocculants were analyzed.The analysis of Al-Ferron timed spectrophotometric showed that Alb content increased with the increase of B value,decreased with increase of preparation temperature,but the preparation temperature is far less than the B value on the influence of aluminum content.The content of Alb in PAC-CTS composite flocculant decreased with the increase of C value.The microstructure will be affected with preparation temperature and B value was found by TEM analysis.With the increase of B value,PAC structure became more three-dimensional.With the increase of preparation temperature,the crystal size of PAC became smaller.PAC-CTS composite flocculant was film shaped with micropores,and the number of micropores gradually increased with the increase of C value.XRD measurement reveal that the effect on the diffraction peaks of PAC with preparation temperature was little.On the contrary,B value had a great influence on the diffraction peaks.With the increase of B value,the diffraction peak intensity of AlCl3·6H2O decreased gradually until disappeared.With the increase of C value,there were several diffraction peak of PAC-CTS composite flocculant disappeared,which indicating that there may be some interaction between PAC and CTS.FT-IR showed that the infrared spectra of PAC was basically consistent in different preparation temperatures.However,with the increase of B value,the AlOH2 bending vibration peak gradually offset,which indicating the formation of chemical bond in PAC was strong influenced by B value.The diffraction peak of newly-formed Al-NH2 in PAC-CTS,which strongly suggested that there were interaction between PAC and CTS in composite flocculant.The flocculation experiments of Reactive Blue 19 and humic acid wastewater with different preparation temperatures and alkalinity PAC verified that the flocculation performance of PAC agreed with its distribution of aluminum.The results showed that among the three kinds of aluminum species in PAC,the flocculation performance was mainly influenced by Alb.Furthermore,the zeta potential were mainly influenced by the content of Ala through the zeta measurement.The flocculation experiment showed pH was one of the key factors that affect the removal rate.The flocculation effect of PAC was the best in neutral and weakly alkaline range(6< pH <9),which was obviously reduced in acidic and alkaline conditions.PAC-CTS composite flocculant was applicable for a wide range of pH and the less dosage for the same removal rate compared with PAC,which indicated that the flocculation performance of PAC-CTS was better than PAC.The effect of turbidity and stirring speed on the flocculation are not obvious compared with pH and dosage.But the lower the stirring speed was,the bigger the floc formed after flocculation,and the fast the settlement rate.The flocculation mechanism of PAC and PAC-CTS composite flocculant were analyzed combined with the flocculation experiments.The electrical neutralization play the major role in flocculation performance of PAC.In addition to the electrical neutralization,PAC-CTS exerts its flocculation performance more by the bridge/adsorption.In summary,the flocculation performance of PAC-CTS composite flocculant was better than PAC,and it’s a new type of high efficient inorganic-organic polymer flocculant,which provides a theoretical basis for practical application.