Harvey O R, Rhue R D
Water Management and Hydrological Sciences, Texas A&M University, 3408 TAMU, College Station, TX 77843, USA.
J Colloid Interface Sci. 2008 Jun 15;322(2):384-93. doi: 10.1016/j.jcis.2008.03.019. Epub 2008 Mar 18.
Multi-component Al-Fe hydr(oxides) are ubiquituous in soil and aquatic environments, where they exhibit biogeochemical controls on nutrients and contaminants. Although, sorption on single-component Al and Fe hydr(oxides) have been extensively studied, limited studies have been done on their multi-component counterparts. In this study, effects of Al/Fe content on the kinetics and energetics of phosphate sorption in a poorly-crystalline co-precipitated mixed Al-Fe hydr(oxide) system were investigated using a combination of traditional batch techniques and flow adsorption calorimetry. Differences in Al/Fe content was found to influence the structural development and anion exchange capacity of the hydr(oxides) and subsequently their phosphate sorption characteristics. Higher structural development decreased phosphate sorption, while higher AEC was associated with increased phosphate sorption, initial sorption rate, and smaller losses in sorption with increasing pH. Results from flow adsorption calorimetry indicated that at pH 4.8 phosphate sorption: (i) occurred irreversibly on anion exchange sites, with a loss of 1.9 moles of AEC per mole of phosphate sorbed, and (ii) was exothermic, with molar heats of adsorption between -25 and -39 kJmol(-1). Molar heats of adsorption were ten times that for anion exchange and independent of hydr(oxide) composition with the amount of energy evolved being directly proportional to the quantity of phosphate sorbed.
多组分铝铁氢氧化物在土壤和水生环境中普遍存在，在这些环境中它们对养分和污染物具有生物地球化学控制作用。尽管对单组分铝和铁的氢氧化物的吸附已进行了广泛研究，但对其多组分对应物的研究却很少。在本研究中，结合传统的批量技术和流动吸附量热法，研究了铝/铁含量对 poorly - crystalline 共沉淀混合铝铁氢氧化物体系中磷酸盐吸附动力学和能量学的影响。发现铝/铁含量的差异会影响氢氧化物的结构发展和阴离子交换容量，进而影响它们的磷酸盐吸附特性。较高的结构发展降低了磷酸盐吸附，而较高的阴离子交换容量与磷酸盐吸附增加、初始吸附速率增加以及随着pH值升高吸附损失较小有关。流动吸附量热法的结果表明，在pH 4.8时磷酸盐吸附：(i) 在阴离子交换位点上不可逆地发生，每吸附一摩尔磷酸盐损失1.9摩尔阴离子交换容量，(ii) 是放热的，吸附热在 - 25至 - 39 kJmol(-1) 之间。吸附热是阴离子交换热的十倍，且与氢氧化物组成无关，释放的能量直接与吸附的磷酸盐量成正比。
