Abstract A surface complexation model of Se(IV) sorption on biotite with one type of strong sorption sites and two types of weak sorption sites were developed based on experimental data obtained from titration, sorption edge and sorption isotherm experiments. Titration data was collected using a batch-wise manner together with backtitration to calibrate the effect of mineral dissolution in 0.01 M KClO4 background electrolytes from pH 3 to 11 in an inert atmosphere glovebox. Further calibrations of the titration curve include proton exchange and cation exchange in which the calculations of cation occupancies on biotite surfaces were taken into account. The sorption edge measurements were determined by measuring the sorption of 10−9 M total Se with a radioactive Se-75 tracer on converted biotite in 0.01 M KClO4 solution from pH 3 to 11. Se sorption was observed to be strongly dependent on pH. Surface complexation modelling was performed by deriving a set of optimized parameters that can fit titration, sorption edge and sorption isotherm (at pH ~7.7) experimental data. A CASTEP code implemented into Materials Studio was used to calculate the site densities and site types on the biotite surfaces. Weak sorption sites with site densities of 3.2 sites/nm2 and 1.4 sites/nm2 were derived from the codes and used in the sorption model. A computer code that coupled PHREEQC with Python was developed for the fitting and optimizing processes. The model was validated by sorption data at pH ~9.5. The results show that the model can provide quantitative predicts of Se(IV) sorption in groundwater conditions of a deep geological repository and help improve the performance assessments by giving more convincing estimates of the release of radionuclides towards aquifers and biosphere.

中文翻译：

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Se(IV)在黑云母上吸附的多位点表面络合模拟

摘要 基于滴定、吸附边缘和吸附等温线实验获得的实验数据，建立了具有一类强吸附位点和两类弱吸附位点的黑云母对Se(IV)吸附的表面络合模型。使用分批方式和反滴定收集滴定数据，以校准在惰性气氛手套箱中从 pH 3 到 11 的 0.01 M KClO4 背景电解质中矿物溶解的影响。滴定曲线的进一步校准包括质子交换和阳离子交换，其中考虑了黑云母表面阳离子占有率的计算。通过使用放射性 Se-75 示踪剂在 0.01 M KClO4 溶液中从 pH 3 到 11 测量转化的黑云母上 10-9 M 总 Se 的吸附来确定吸附边缘测量值。观察到Se吸附强烈依赖于pH。表面络合建模是通过导出一组可以拟合滴定、吸附边缘和吸附等温线（pH ~ 7.7）实验数据的优化参数来进行的。在 Materials Studio 中实施的 CASTEP 代码用于计算黑云母表面上的站点密度和站点类型。位点密度为 3.2 个位点/nm2 和 1.4 个位点/nm2 的弱吸附位点来自代码并用于吸附模型。为拟合和优化过程开发了将 PHREEQC 与 Python 相结合的计算机代码。该模型通过 pH ~ 9.5 下的吸附数据进行了验证。