磁性Mg/Al-LDHs制备条件对其吸附除磷性能的影响

为提高粉末状水滑石吸附剂的工程应用性,采用共沉淀法制备了磁性Mg/Al水滑石(Layered Double Hydroxides,LDHs).结合XRD、FTIR、SEM及VSM等材料表征结果,考察了制备条件(磁基质投加量、金属物质的量比和层间阴离子)对其吸附除磷性能、磁学性能及结构特征的影响.结果表明,在Fe_3O_4与Mg~(2+)物质的量比为0.02、Mg/Al物质的量比为2∶1和层间阴离子为Cl~-/OH~-的条件下制备出的磁性Mg/Al-LDHs对TP吸附性能最好,平衡吸附量可达49.60 mg·g~(-1);比饱和磁化强度为2.78 emu·g~(-1),能够实现吸附剂的快速高效磁分离回收.层间阴离子种类对水滑石焙烧前后吸附除磷性能有一定的影响:经高温焙烧后,层间含有CO■的水滑石吸磷能力虽有所提高,但仍低于无CO■型LDHs.因此,在水滑石制备过程中避免使用碳酸盐作为共沉碱原料,这样无需焙烧即可获得较高吸磷能力的吸附剂.

Adsorption performance of phosphorus by magnetic Mg/Al-LDHs prepared under different conditions

In order to enhance the engineering application of powdered hydrotalcite adsorbents, magnetic Mg/Al hydrotalcites (layered double hydroxides, Mg/Al-LDHs) were prepared using co-precipitation method. Combined with the results of XRD, FTIR, SEM and VSM, the effects of Mg/Al-LDHs'' preparation conditions (magnetic matrix dosage, metal molar ratio and interlayer anion) on their phosphorus adsorption, magnetic properties and structural characteristics were investigated. The results show that the magnetic Mg/Al-LDHs prepared with the molar ratio of Fe₃O₄ to Mg²⁺ at 0.02, Mg/Al molar ratio at 2:1 and an interlayer anions of Cl^-/OH^- had the optimal adsorption performance to total phosphorus (TP), with an equilibrium adsorption capacity reaching 49.60 mg·g^-1, while their specific saturation magnetization intensity reached 2.78 emu·g^-1, which enabled rapid and efficient magnetic separation and recovery of adsorbent. It is found that the interlayer anions had a certain influence on the phosphorus adsorption by hydrotalcites before and after calcination. After calcination, the phosphorus absorption capacity of hydrotalcites containing CO₃^2- in the interlayer improved, but is still lower than that of LDHs without CO₃^2-. Therefore, in the preparation of hydrotalcites, carbonate should not be used as the raw material of co-precipitation alkali, so that the adsorbent with high phosphorus absorption ability could be obtained without calcination.