Classification
445.1 Water Treatment Techniques - 451.2 Air Pollution Control - 451.4 - 802.1 Chemical Plants and Equipment - 802.3 Chemical Operations - 804.2 Inorganic Compounds
445.1 Water Treatment Techniques - 451.2 Sewage Treatment - 451.4 Industrial Wastes Treatment and Disposal - 802.1 Chemical Plants and Equipment - 802.3 Chemical Operations - 804.2 Inorganic Compounds
Type
Microstructure and surface elemental distribution of granular AA were altered by NaOH impregnation as indicated by BET, SEM and XPS analyses (Fig. 2A–C). It is well known that NaOH reacts with AA to form AlO2−, which dissolves in water at high alkalinity [30], while Al(OH)3 precipitation at low alkalinity leads to the clogging of the MAA pores [31]. As shown in Fig. S6 (Supporting Information), AA and MAA have significant hysteresis loops, which indicates abundant mesopores and favorable adsorption [32]. ThePs andPv of MAA firstly increased and then decreased with increasing NaOH concentration. The maximum total Pv (0.447 cm3/g) and Ps (3.58 nm) corresponded to the NaOH concentrations of 15 and 20 g/L, respectively. Increasing the NaOH concentration to 25 g/L NaOH led to complete reaction with the surface of MAA resulting in a porosity decrease. The change in surface structure shown by the SEM image also proves the change of pore structure of MAA as shown in Fig. 2B. The increase in scale-like structures in yellow circles which was reported to increase the pore structure of the material demonstrated an increase in material porosity [33]. The surface of MAA included scale-like structures as compared to AA, and this structure first increased and then decreased with the increase of NaOH concentration. Similar results were found by Lin et al. [34] and Wang et al. [35], who also suggested that only the NaOH with appropriate concentration could create mesoporous and scale-like structure of modified materials.XPS analyses indicated elemental variations on the surface of MAA. As shown in Fig. S8 (Supporting Information), Al 2p and O1s located at 531 and 73 eV are the major components of AA and MAA [36,37]. Compared with AA, the surface of MAA was successfully loaded with Na element as shown in Fig. 2C. The MAA Na1s and Na-O was located at 1070.9–1071.3 eV and 496 eV, respectively which may be due to the presence of Na-O structures [30,38,39]. The Na loading increased and then decreased with the increasing of NaOH concentration, as shown in Table S3 (Supporting Information) and Fig. 2C. Alkaline solution modification can enhance the alkalinity of AA, and the ability to adsorb Na can be improved [40,41]. However, less abundant pore structure could not ensure sufficient Na adsorption in high alkaline solution. This resulted in a decrease in Na loading for the 25 g/L NaOH- MAA.Fig. 3A and B depict the MD performance with different MAA filtration media. Scaling on membrane led to the reduction in membrane performance, which included the formation of scaling in the polarization (boundary) layer and homogeneous scaling in the bulk solution deposited on the membrane surface to increase the mass transfer resistance [42,43]. As shown in Fig. 3C, the SI is high in the polarization layer compared to the bulk solution, which leads to scaling in the polarization layer earlier than in the solution. The SI in the polarization layer was higher than the SI for homogeneous scaling, which led to the rapid formation of homogeneous scaling and heterogeneous scaling in the polarization layer at the beginning. However, this did not result in a significant change in MD flux due to the limited amount of scaling material available in the polarization layer. As the water recovery increased, the increase in feed water SI led to a large amount of homogeneous scaling forming in solution and depositing on the membrane surface, at which point the MD flux decreased dramatically and the permeate conductivity increased. Thus, the overall change in flux showed a steady and then rapid decline and conductivity increased dramatically at a certain point [44]. MD performance was greatly influenced by MAA properties in granular filter. Increasing NaOH concentration, mass ratio of AA to NaOH solution and impregnation time resulted in a higher MD final flux and lowe
