Beattie D A, Chapelet J K, Gräfe M, Skinner W M, Smith E
Ian Wark Research Institute, University of South Australia, Mawson Lakes Campus, SA 5095, Australia.
Environ Sci Technol. 2008 Dec 15;42(24):9191-6. doi: 10.1021/es801767b.
Despite the existence of many single ion sorption studies on iron and aluminum oxides, fewer studies have been reported that describe cosorption reactions. In this work, we present an in situ ATR FTIR study of synergistic adsorption of sulfate (SO4) and copper (Cu) on goethite, which is representative of the minerals and ions present in mine wastes, acid sulfate soils, and other industrial and agricultural settings. Sulfate adsorption was studied as a function of varying pH, and as a function of increasing concentration in the absence and presence of Cu. The presence of Cu ions in solution had a complex effect on the ability of SO4 ions to be retained on the goethite surface with increasing pH, with complete desorption occurring near pH 7 and 9 in the absence and presence of Cu, respectively. In addition, Cu ions altered the balance of inner vs outer sphere adsorbed SO4. The solid phase partitioning of SO4 at pH 3 and pH 5 was elevated by the presence of Cu; in both cases Cu increased the affinity of SO4 for the goethite surface. Complementary ex situ sorption edge studies of Cu on goethite in the absence and presence of SO4 revealed that the Cu adsorption edge shifted to lower pH (6.3 --> 5.6) in the presence of SO4, consistent with a decrease of the electrostatic repulsion between the goethite surface and adsorbing Cu. Based on the ATR FTIR and bulk sorption data we surmise that the cosorption products of SO4 and Cu at the goethite-water interface were not in the nature of ternary complexes under the conditions studied here. This information is critical for the evaluation of the onset of surface precipitates of copper-hydroxy sulfates as a function of pH and solution concentration.
尽管已有许多关于铁和铝氧化物对单一离子吸附的研究，但描述共吸附反应的研究报告较少。在本研究中，我们进行了一项原位衰减全反射傅里叶变换红外光谱（ATR FTIR）研究，考察了硫酸盐（SO4）和铜（Cu）在针铁矿上的协同吸附，针铁矿是矿山废弃物、酸性硫酸盐土壤以及其他工农业环境中存在的矿物和离子的代表。研究了硫酸盐吸附随pH值变化的情况，以及在有无铜存在时随浓度增加的吸附情况。溶液中铜离子的存在对SO4离子在针铁矿表面的保留能力随pH值升高产生了复杂影响，在无铜和有铜存在时，分别在pH约7和9时发生完全解吸。此外，铜离子改变了内层与外层吸附SO4的平衡。在pH 3和pH 5时，铜的存在提高了SO4在固液相间的分配；在这两种情况下，铜都增加了SO4对针铁矿表面的亲和力。对有无SO4存在时铜在针铁矿上的非原位吸附边界的补充研究表明，在有SO4存在时，铜的吸附边界向较低pH值（6.3 --> 5.6）移动，这与针铁矿表面和吸附的铜之间静电排斥力的降低一致。基于ATR FTIR和批量吸附数据，我们推测在此研究条件下，针铁矿-水界面处SO4和Cu的共吸附产物并非三元络合物的性质。该信息对于评估作为pH值和溶液浓度函数的羟基硫酸铜表面沉淀的起始情况至关重要。
