Arsenite and arsenate adsorption on ferrihydrite: Kinetics, equilibrium, and adsorption envelopes
Arsenite and arsenate adsorption on ferrihydrite: Kinetics, equilibrium, and adsorption envelopes
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DOI：
10.1021/es970421p
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发表时间：
1998-02-01
影响因子：
11.4
通讯作者：
Loeppert, RH
中科院分区：
文献类型：
--
作者：
Raven, KP;Jain, A;Loeppert, RH
由于其毒性，砷引起了相当大的环境问题。它在自然系统中的溶解度受到氧化铁表面吸附的强烈影响。本研究的目的是在严格控制的条件下比较亚砷酸盐和砷酸盐在水铁矿上的吸附行为，包括吸附动力学、吸附等温线以及 pH 对吸附的影响。吸附反应相对较快，反应几乎在最初的几个小时内完成。在相对较高的砷浓度下，亚砷酸盐与水铁矿的反应速度比砷酸盐更快，即更快达到平衡，但在低砷浓度和低 pH 条件下，砷酸盐吸附更快。在pH 4.6（括号中的pH 9.2）下，亚砷酸盐和砷酸盐的吸附最大值分别约为0.60 (0.58) 和0.25 (0.16) mol(As)、mol(Fe)(-1)。高亚砷酸盐保留率完全排除了其作为表面吸附物质的保留，表明水铁矿可能转化为亚砷酸铁相，尽管这种可能性尚未通过光谱研究证实。当初始砷浓度大于或等于0.27 mol(As) kg(-1)水铁矿时，在pH 4-9范围内，总体趋势是随着pH的增加，砷酸盐吸附增加，砷酸盐吸附减少。当初始As浓度为0.27-0.80 mol(As), kg(-1)水铁矿时,吸附包络线在大约pH 6-7.5处交叉,即在较低pH值下吸附砷酸盐浓度相对大于吸附亚砷酸盐浓度,而在较高pH值时吸附亚砷酸盐浓度较高。在水铁矿的最高初始砷浓度为13.3 mol(As) kg(-1)时，在大约pH 9.0时观察到亚砷酸盐吸附的明显吸附最大值，这与H3AsO30的第一个pK(a) (9.2)密切对应，而随着pH从3增加到11，砷酸盐吸附持续下降。
Because of its toxicity, arsenic is of considerable environmental concern. Its solubility in natural systems is strongly influenced by adsorption at iron oxide surfaces. The objective of this study was to compare the adsorption behavior of arsenite and arsenate on ferrihydrite, under carefully controlled conditions, with regard to adsorption kinetics, adsorption isotherms, and the influence of pH on adsorption. The adsorption reactions were relatively fast, with the reactions almost completed within the first few hours. At relatively high As concentrations, arsenite reacted faster than arsenate with the ferrihydrite, i.e., equilibrium was achieved sooner, but arsenate adsorption was faster at low As concentrations and low pH. Adsorption maxima of approximately 0.60 (0.58) and 0.25 (0.16) mol(As), mol(Fe)(-1) were achieved for arsenite and arsenate, respectively, at pH 4.6 (pH 9.2 in parentheses). The high arsenite retention, which precludes its retention entirely as surface adsorbed species, indicates the likelihood that ferrihydrite was transformed to a ferric arsenite phase, although this possibility has yet to be confirmed by spectroscopic studies. The general trend at initial arsenic concentrations greater than or equal to 0.27 mol(As) kg(-1) ferrihydrite within the pH range of 4-9 was increasing arsenite adsorption and decreasing arsenate adsorption with increasing pH. At initial As concentrations of 0.27-0.80 mol(As), kg(-1) ferrihydrite, the adsorption envelopes crossed at approximately pH 6-7.5, i.e., adsorbed arsenate concentrations were relatively greater than adsorbed arsenite concentrations at lower pH values whereas adsorbed arsenite was greater at higher pH. At the highest initial arsenic concentration of 13.3 mol(As) kg(-1) ferrihydrite, a distinct adsorption maximum was observed for arsenite adsorption at approximately pH 9.0, which corresponds closely to the first pK(a) (9.2) of H3AsO30, whereas there was a continuous drop in arsenate adsorption with increasing pH from 3 to 11.