Role of Al speciation on humic acid coagulation
The hydrolyzed species distribution of A1 coagulants ale significantly affected by pH,which determines the coagulation mechanisms affecting the removal efficiency of natural organic matter(NOM).The aim of this study is to investigate the role of A1 speciafion on the coagulation of humic acid(HA).Two polyaluminum chloride(PACI)coagulants,one commercial PACl(termed PACl)and another custom-made PACl(designated PACl-Al13)containing Al13 with 7％and 96％of total Al concentration.Respectively,were appfied to mix with humic acid in water.The A1-HA floes formed after coagulafion at various pH values were identified by Fourier transform infrared(FTIR)and solid-state27 Al nuclear magnettc resonance(27AI NMR)to verify the reaction mechanisms between HA and A1 species.The morpholog)r of Al-HA floes was examined by wet scanning electron microscopy(WSEM).The results have shown that leSS dosage was required for organic coagulation by PACl-Al3 than that by PACl at pH ranging from 4 to 6,at which the optimum dosages of PACl and PACl-Al13 were observed due to Al-HA complexation as well as charge neutralization by monomeric Al and Al13.At pH 6,the opttmum dosage for PACl-Al13 was lower than for PACl.Indicating that charge neutralization is the predominant mechanism at acidic pH.The FTIR spectra revealed that carboxylic groups(-COOH)of HA form complexes with monomenc Al as well as Al13 polycafion.WSEM images have illustrated that the PACl-HA floe turned into a linear-shaped structure while the PACl-Al13-floc was slightly cufled.In addition,the solid-state“Al NMR spectra have indicated that a few monomeric Al as well as oligmeric Al are generated via the depolymerization of Al13 after the coagulation of PACl and PACl-Al13 For PACl and PACl-Al13 coagulation of humic acids,the interaction mechanisms between predominant hydrolyzed Al species and HA are depicted in Fig.1.At pH 6,a considerable amount of A13+ species of PACl preferentially binds to HA through complexation.At such acidic pH.free A13+species could in-situ transform into Al13 which would further react with HA to form Al13.HA complexes.Certain percentage of formed Al13-HA complexes could be decomposed to form monomeric or oligomeric A1.In addition,some Al species have precipitated as Al(OH)3 to remove HA by adsorption and co-precipitation.Since the in-situ formed Al13-HA complexes ale not stable,they gradually transform into octahedral Al-HA complexes.On the other hand,because the voluminous preformed Al13 species in PACl-Al13 coagulant is fairly stable at acidic condition,only a small number of Al13-HA complexes are decomposed into monomenc Al;as a conscquence,either Al-HA complexes or Al(OH)3 precipitates could form co-precipitate.
Coagulation PACl Al13 NOM humic acid
Chihpin HUANG Jr-Lin LIN Jinyi HU
Institute of Environmental Engineering National Chiao Tung University Hsmchu,Taiwan
国际会议
西安
英文
63-64
2008-05-15（万方平台首次上网日期，不代表论文的发表时间）