Abstract

Chromium is one of the most hazardous inorganic water pollutants which is constantly released into water resources by natural and industrial processes. Microfiltration membranes (with pore sizes between 0.1–10 μm) cannot separate chromium ions and hence nanofiltration membranes (with pore sizes between 0.5–2 nm) are necessary which need high pressure pumps. Using adsorptive membranes, i.e. membranes which can adsorb impurities without using any extra adsorptive particles, is a new and developing method for water treatment which can be considered as a combination of adsorption and membrane technology. In this paper, clay-based adsorptive microfiltration membranes were successfully synthesized for chromium removal from water. 80 wt % of bentonite and 20 wt % of carbonates (calcium, magnesium and their mixture) were mixed, uniaxially pressed, dried, and fired at 1100°C for 3 h. Then, phase analyses of the samples, their physical and mechanical properties, microstructure, mean pore size and also their ability for chromium removal from water were studied. Results showed that the addition of carbonates lead the porosity to increase while contrary to organic pore formers like starch, due to the formation of phases like wollastonite, the mechanical strength not only didn’t collapse but also improved. It was seen that Cr³⁺ ions were removed from water up to 95% and regarding that the mean pore sizes of the microfiltration membranes used in this work (0.6–2.5 μm) were 10 000 times bigger than the size of Cr³⁺ ions (0.615 A), it was deduced that Cr³⁺ ions were removed through adsorption mechanism and the microfiltration membrane prepared the media for adsorption. By analyzing the filtered water and observation of Ca²⁺ ions in it, it was concluded that ion exchange was the main mechanism. Hence, a combination of membrane filtration and adsorption was achieved for water treatment which made microfiltration membranes act as nanofiltration ones and considering that the concentration of Cr³⁺ ions in real drinking water resources is less than 5 ppm (which is regarded in this research), it can be said that these low-cost adsorptive microfiltration membranes can be used to gain high quality drinking water.

中文翻译：

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粘土基吸附微滤膜的合成

摘要

铬是最危险的无机水污染物之一，通过自然和工业过程不断释放到水资源中。微滤膜（孔径在 0.1–10 μm 之间）不能分离铬离子，因此需要使用高压泵的纳滤膜（孔径在 0.5–2 nm 之间）。使用吸附膜，即在不使用任何额外的吸附颗粒的情况下吸附杂质的膜，是一种新兴的水处理方法，可以认为是吸附和膜技术的结合。在本文中，成功合成了粘土基吸附微滤膜，用于去除水中的铬。将 80 wt% 的膨润土和 20 wt% 的碳酸盐（钙、镁及其混合物）混合、单轴压制、干燥、并在 1100°C 下烧制 3 小时。然后，研究了样品的相分析、它们的物理和机械性能、微观结构、平均孔径以及它们从水中去除铬的能力。结果表明，碳酸盐的添加导致孔隙率增加，而与淀粉等有机造孔剂相反，由于硅灰石等相的形成，机械强度不仅没有坍塌，而且有所提高。可以看出，Cr 机械强度不仅没有崩溃，反而有所提高。可以看出，Cr 机械强度不仅没有崩溃，反而有所提高。可以看出，Cr^{3+离子从水中去除高达 95%，并且关于本工作中使用的微滤膜的平均孔径（0.6-2.5 μm）是 Cr 3+}离子（0.615 A）尺寸的 10 000 倍，推测Cr ³⁺离子通过吸附机理被去除，微滤膜制备了吸附介质。通过分析过滤后的水和观察其中的Ca ²⁺离子，得出离子交换是主要机理的结论。因此，在水处理中实现了膜过滤和吸附的结合，使微滤膜充当纳滤膜，并考虑到Cr ^3+的浓度实际饮用水资源中的离子含量低于5 ppm（本研究认为），可以说这些低成本的吸附式微滤膜可以用来获得高质量的饮用水。