Kirwan Luke J, Fawell Phillip D, van Bronswijk Wilhelm
A. J. Parker Cooperative Research Centre for Hydrometallurgy, Department of Applied Chemistry, Curtin University of Technology, G.P.O. Box U1987, Perth, WA 6845, Australia.
Langmuir. 2004 May 11;20(10):4093-100. doi: 10.1021/la036248u.
FTIR-ATR was used to examine in situ the interaction of polyacrylate and hematite at pH 13. Static light scattering and mobility measurements were used to assess solution polyacrylate dimensions and hematite surface charge, respectively. Polyacrylate adsorption occurred only with the addition of electrolyte (e.g., NaCl), and it was found that excess cations, up to approximately 1 M, facilitated adsorption, above which the effect was found to plateau. At pH 13 and at low ionic strength, adsorption of polyacrylate onto hematite is facilitated by cations in solution shielding both the negative acrylate functionality of the polymer and the negative hematite surface. The shielding of the hematite surface continues to increase with increasing salt concentration up to a measured 3 M. Similarly, the shielding of the polymer increased with electrolyte concentration up to approximately 1 M salt, beyond which no further increase in shielding was observed. At this concentration the polymer assumes a finite minimum size in solution that ultimately limits the amount adsorbed. The dimension of the polymer in solution was found to be independent of monovalent cation type. Thus, at high pH and high ionic strength adsorption is determined by the degree of hematite surface charge reduction. The cation-hematite surface interaction was found to be specific, with lithium leading to greater polyacrylate adsorption than sodium, which was followed by cesium. The stronger affinity of lithium for the hematite surface over sodium and cesium is indicative of the inverse lyotropic adsorption series and has been rationalized in the past by the "structure-making-structure-breaking" model. These results provide a useful insight into the likely adsorption mechanism for polyacrylate flocculants at high pH and ionic strength onto residues in the Bayer processing of bauxite.
采用傅里叶变换红外光谱-衰减全反射（FTIR-ATR）原位研究了在pH值为13时聚丙烯酸酯与赤铁矿的相互作用。分别使用静态光散射和迁移率测量来评估溶液中聚丙烯酸酯的尺寸和赤铁矿的表面电荷。聚丙烯酸酯仅在添加电解质（如NaCl）时发生吸附，并且发现过量的阳离子（高达约1 M）促进吸附，超过此浓度后效果趋于平稳。在pH值为13且离子强度较低时，溶液中的阳离子屏蔽了聚合物的负丙烯酸酯官能团和赤铁矿的负表面，从而促进了聚丙烯酸酯在赤铁矿上的吸附。随着盐浓度增加至实测的3 M，赤铁矿表面的屏蔽作用持续增强。同样，随着电解质浓度增加至约1 M盐，聚合物的屏蔽作用增强，超过此浓度后未观察到屏蔽作用进一步增加。在此浓度下，聚合物在溶液中呈现出有限的最小尺寸，最终限制了吸附量。发现溶液中聚合物的尺寸与单价阳离子类型无关。因此，在高pH值和高离子强度下，吸附取决于赤铁矿表面电荷减少的程度。发现阳离子与赤铁矿表面的相互作用具有特异性，锂导致的聚丙烯酸酯吸附量大于钠，其次是铯。锂对赤铁矿表面的亲和力强于钠和铯，这表明了反溶致吸附序列，过去已通过“结构形成-结构破坏”模型进行了合理解释。这些结果为聚丙烯酸酯絮凝剂在高pH值和离子强度下对铝土矿拜耳法加工残渣的可能吸附机制提供了有用的见解。
