Masue Yoko, Loeppert Richard H, Kramer Tim A
Department of Soil and Crop Sciences, Texas A&M University, College Station, Texas 77843-2474, USA.
Environ Sci Technol. 2007 Feb 1;41(3):837-42. doi: 10.1021/es061160z.
Although arsenic adsorption/desorption behavior on aluminum and iron (oxyhydr)oxides has been extensively studied, little is known about arsenic adsorption/desorption behavior by bimetal Al:Fe hydroxides. In this study, influence of the Al:Fe molar ratio, pH, and counterion (Ca2+ versus Na+) on arsenic adsorption/desorption by preformed coprecipitated Al:Fe hydroxides was investigated. Adsorbents were formed by initial hydrolysis of mixed Al3+/ Fe3+ salts to form coprecipitated Al:Fe hydroxide products. At Al:Fe molar ratios < or = 1:4, Al3+ was largely incorporated into the iron hydroxide structure to form a poorly crystalline bimetal hydroxide; however, at higher Al:Fe molar ratios, crystalline aluminum hydroxides (bayerite and gibbsite) were formed. Although approximately equal As(V) adsorption maxima were observed for 0:1 and 1:4 Al:Fe hydroxides, the As(III) adsorption maximum was greater with the 0:1 Al: Fe hydroxide. As(V) and As(III) adsorption decreased with further increases in Al:Fe molar ratio. As(V) exhibited strong affinity to 0:1 and 1:4 Al:Fe hydroxides at pH 3-6. Adsorption decreased at pH > 6.5; however, the presence of Ca2+ compared to Na+ as the counterion enhanced As( retention by both hydroxides. There was more As(V) and especially As(III) desorption by phosphate with an increase in Al:Fe molar ratio.
尽管砷在铝和铁的（氢）氧化物上的吸附/解吸行为已得到广泛研究，但对于双金属氢氧化铝铁对砷的吸附/解吸行为却知之甚少。在本研究中，考察了铝铁摩尔比、pH值和抗衡离子（Ca²⁺与Na⁺）对预先形成的共沉淀氢氧化铝铁吸附/解吸砷的影响。吸附剂是通过混合Al³⁺/Fe³⁺盐的初始水解形成共沉淀的氢氧化铝铁产物而形成的。当铝铁摩尔比≤1:4时，Al³⁺大量掺入氢氧化铁结构中形成结晶度差的双金属氢氧化物；然而，在较高的铝铁摩尔比下，会形成结晶态的氢氧化铝（水铝石和三水铝石）。尽管对于0:1和1:4的氢氧化铝铁观察到的As(V)吸附最大值大致相等，但0:1的氢氧化铝铁对As(III)的吸附最大值更大。随着铝铁摩尔比的进一步增加，As(V)和As(III)的吸附量降低。在pH 3 - 6时，As(V)对0:1和1:4的氢氧化铝铁表现出很强的亲和力。在pH > 6.5时吸附量降低；然而，与Na⁺作为抗衡离子相比，Ca²⁺的存在增强了两种氢氧化物对As的保留。随着铝铁摩尔比的增加，磷酸盐对As(V)尤其是As(III)的解吸作用增强。
