Fe(Ⅱ)、Fe(Ⅲ)对砷与不同分子量腐植酸络合性能的影响

Effect of Fe(Ⅱ)/Fe(Ⅲ) on complexation properties of arsenic and humic acid with different molecular weights

以腐植酸(HA)代表天然有机质,采用平衡透析和超滤的方法研究铁离子(Fe(Ⅱ)、Fe(Ⅲ))对不同分子量HA与砷离子(As(V)、As(Ⅲ))络合作用的影响,并利用红外光谱(FT-IR)表征其络合特征.结果发现,Fe(Ⅱ)和Fe(Ⅲ)均能增强HA络合As能力,且对As(V)络合能力的增强作用大于As(Ⅲ);pH值显著影响HA络合As能力;溶解性有机碳(DOC)浓度由5mg/L增大到200mg/L,As络合百分比随之增加,此时HA-Fe(Ⅲ)络合As(Ⅲ)百分比最大,为24.55%;初始As浓度由10μg/L增加1000μg/L,As络合百分比随之降低,其中HA-Fe(Ⅲ)络合As(Ⅲ)百分比最低,为3.11%.相同环境条件下,分子量>100kDa络合As百分比最大,其中HA-Fe(Ⅱ)络合As(Ⅲ)的百分比最高为26.43%;分子量小于10kDa的HA络合As百分比明显高于其他分子量的HA.Fe的增强作用主要源于Fe与羧基形成桥梁再与As络合形成三元络合物.

Humic acid(HA) was used to represent natural organic matter,and the effects of Iron ions(Fe(Ⅱ)/Fe(Ⅲ)) on the complexation of HA with arsenic(As(V)/As(Ⅲ)) of different molecular weights were investigated by equilibrium dialysis and ultrafiltration,and the complexation characteristics were characterized by infrared spectroscopy(FT-IR).Both Fe(Ⅱ) and Fe(Ⅲ)enhanced the As complexation ability of HA,and the enhancement effect on As(V) complexation ability was greater than that of As(Ⅲ);pH significantly affected the As complexation ability of HA;the percentage of As complexation increased with the increase of dissolved organic carbon(DOC) concentration of HA from 50 to 200mg/L,and the percentage of HA-Fe(Ⅲ) complexation was the maximum at 24.55%.Increasing the initial As concentration from 10μg/L to 1000μg/L,the percentage of As complexation decreased,with the minimum As(Ⅲ) complexation percentage by HA-Fe(Ⅲ) at 3.11%.Under the same environmental conditions,the percentage of As complexed with molecular weight more than 100kDa was the highest,and the percentage of As(Ⅲ) complexed at HA-Fe(Ⅱ) was 26.43%;The percentage of As complexed at HA with molecular weight less than 10kDa was significantly higher than that at other molecular weights.The enhancement of Fe was mainly due to the formation of a bridge between Fe and carboxyl groups of HA and then complexation with As to form a ternary complex.