Synthesis of zeolite/hydrous lanthanum oxide composite from coal fly ash for efficient phosphate removal from lake water

• Zeolite/hydrous lanthanum oxide composite was synthesized from coal fly ash.
• The material was highly efficient to capture phosphate from lake water.
• The performance of phosphate removal was correlated with properties of lake water.
• pH effect and pH reversibility of phosphate adsorption was investigated.
• The material showed additional ability to retain cationic pollutants.

We investigated the use of coal fly ash as a raw material for the production of a zeolite/hydrous lanthanum oxide hybrid material (ZHLO) and as a means of controlling internal phosphorus loading in lakes. We found that the use of ZHLO, as a method for capturing phosphate from five lake water samples, was considerably more efficient than the existing alum-treatment method. There was some variability in the performance of the ZHLO-method in different lake waters but we noted that, within the La/P molar ratio range of between 2:1 and 4:1, we were able to attain an almost-complete removal of phosphate. Correlation analysis indicated that high alkalinity reduced the performance of phosphate binding. Phosphate adsorption by ZHLO was found to decrease with increasing pH. The phosphate adsorbed at acidic pH levels was partly released with increasing pH, while phosphate that was in equilibrium solution at high pH was adsorbed when the pH declined. The extent of reversibility when using the ZHLO method was much lower than that observed when using the alum treatment method. FTIR measurements showed that the monodentate surface species of ≡La-OPO3 was formed via a ligand exchange mechanism. Moreover, ZHLO could also function as a means of removing cationic pollutants. This has important implications in terms of preventing the release of toxic substances (such as manganese and ammonium) from sediments in eutrophic lakes.

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