Phase Regulation of Alkali Heat Activated Fly Ash Based Geopolymer Composites and Its Phosphorus Removal Performance
In order to improve the phosphorus removal effect of geopolymer effectively,fly ash geopolymer composite rich in LDHs was synthesized in situ using alkali heat-activated high-alumina fly ash as precursor,calcium hydroxide-calcium sulfate dihydrate as mixed activators.The main mineral composition of the fly ash,the alkali heat-activated fly ash and the alkali heat-activated fly ash geopolymer were analyzed by XRD and SEM.The phosphorus removal effect of alkali heat-activated fly ash geopolymer composites was investigated by static adsorption test.The results show that alkali heat activation can transform the mullite and corundum phases into active aluminosilicate and silicate.The crystalline phase minerals of the alkali heat activated fly ash geopolymer excited by the mixture of calcium hydroxide and calcium sulfate dihydrate are mainly zeolite phase(4A zeolite,stellerite,laumontite)and the layered double hydroxide phase of hydrocalumite and AFt,which have the function of nitrogen and phosphorus removal.When the mass ratio of calcium hydroxide to calcium sulfate is 1∶1,the alkali heat-activated fly ash geopolymer have the best adsorption effect on H2PO4--P.Under the adsorption conditions of an initial H2PO4--P concentration of 100 mg/L and solid-liquid mass ratio of 1∶100,the adsorption capacity is 9.913 mg/g,and the removal rate is 99.13%.
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