Phosphate recovery from aqueous solution by K-zeolite synthesized from fly ash for subsequent valorisation as slow release fertilizer

Mehrez Hermassi; Cesar Valderrama; Oriol Font; Natalia Moreno; Xavier Querol; Narjès Harrouch Batis; Jose Luis Cortina

doi:10.1016/j.scitotenv.2020.139002

Phosphate recovery from aqueous solution by K-zeolite synthesized from fly ash for subsequent valorisation as slow release fertilizer

Sci Total Environ. 2020 Aug 20:731:139002. doi: 10.1016/j.scitotenv.2020.139002. Epub 2020 Apr 26.

Authors

Mehrez Hermassi¹, Cesar Valderrama², Oriol Font³, Natalia Moreno³, Xavier Querol³, Narjès Harrouch Batis⁴, Jose Luis Cortina⁵

Affiliations

¹ Cranfield Water Science Institute, Vincent Building, Cranfield University, Bedfordshire MK43 0AL, UK; Dept. Biol. Chem. Eng., National Institute of Applied Sciences and Technology (INSAT), University of Carthage (, Tunisia). Electronic address: hermassi.mehrez@gmail.com.
² Chemical Engineering Department, Barcelona Research Center for Multiscale Science and Engineering Escola d'Enginyeria de Barcelona Est (EEBE), Universitat Politècnica de Catalunya (UPC)-BarcelonaTECH, C/ Eduard Maristany 10-14, Campus Diagonal-Besòs, 08930 Barcelona, Spain.
³ Environmental Geochemistry and Atmospheric Research Group (EGAR), Institute of Environmental Assessment and Water Research-Severo Ochoa Excellence Center (IDAEA), Spanish Council of Scientific Research (CSIC), Jordi Girona 18-26, 08034 Barcelona, Spain.
⁴ Dept. Biol. Chem. Eng., National Institute of Applied Sciences and Technology (INSAT), University of Carthage (, Tunisia).
⁵ Chemical Engineering Department, Barcelona Research Center for Multiscale Science and Engineering Escola d'Enginyeria de Barcelona Est (EEBE), Universitat Politècnica de Catalunya (UPC)-BarcelonaTECH, C/ Eduard Maristany 10-14, Campus Diagonal-Besòs, 08930 Barcelona, Spain.; CETaqua, Carretera d'Esplugues 75, 08940 Cornellà de Llobregat, Spain.

PMID: 32417474
DOI: 10.1016/j.scitotenv.2020.139002

Abstract

The sorption of phosphate by K-zeolites synthesized from fly ash (FA) by hydrothermal conversion is investigated in this study. The aim is the synthesis of Ca bearing K-zeolites to recover phosphate from urban and industrial wastewater effluents. The loaded zeolites are considered as a by-products rich in essential nutrients such K and P (KP1) with a potential use as slow release fertilizer. A number of synthesis conditions (temperature, KOH-solution/FA ratio, KOH concentration, and activation time) were applied on two FA samples (FA-TE and FA-LB) with similar glass content but different content of crystalline phases, to optimize the synthesis of a zeolitic sorbent suitable for the subsequent phosphate uptake. Merlinoite and W rich zeolitic products synthesized from FA-LB and FA-TE were found to have sorption properties for phosphate removal. A maximum phosphate sorption capacity of 250 mgP-PO₄/g and 142 mgP-PO₄/g for the zeolitic products selected (KP1-LB and KP1-TE, respectively) was achieved. The dominant phosphate sorption mechanism, in the pH range (6-9) of treated wastewater effluents, indicated that sorption proceeds via a diffusion-controlled process involving phosphate ions coupled with calcium supply dissolution from K-zeolitic products and subsequent formation of brushite (CaHPO₄ 2H₂O(s)). The phosphate loaded sorbent containing a relatively soluble phosphate mineral is appropriate for its use as a synthetic slow release fertilizer. The simultaneous valorisation of fly ash waste and the P recovery from treated wastewaters effluents, (a nutrient with scarce natural resources and low supply) by obtaining a product with high potential for land restoration and agriculture will contribute to develop one example of circularity.

Keywords: Brushite; Fly ash; Phosphate recovery; Potassium zeolite; Sorption; Treated wastewater.