Abstract
Magnetic biochar derived from agricultural biomass has been recognized as a cost-effective biochar sorbent for phosphate removal. This study evaluated the use of novel Fe/Mg-biochar nanocomposites (WBC1x), prepared by impregnating ground walnut shell in a solution with a different molar ratio of Fe2+ to Mg2+, then pyrolyzing slowly, at a temperature of 600 °C, to remove phosphate. The results showed that MgO and Fe3O4 were loaded onto the biochar successfully through the impregnation-pyrolysis method and the composites were able to be separated easily by magnetic field. Meanwhile, a higher surface area and point of zero charge on WBC1x were observed compared to the non-magnetic biochar (WBC). Moreover, the isothermal adsorption and kinetics data further suggested the that phosphate adsorption onto WBC1x resulted from chemisorption. Additionally, the maximum phosphate adsorption capacity of WBC1x was 6.9 mg.g−1, obtained though the Langmuir–Freundlich model, which was threefold higher than WBC, where MgO addition could enhance the adsorption capacity of WBC1x markedly by improving the surface charge.
Highlights
The widespread occurrence of phosphate in the aquatic environment due to human activities may pose a threat to the ecosystem [1]
In WBC1x, O% is highest (11.66%) while C% is lowest in WBC1x; as a consequence, greater O/C is obtained in WBC1x compared to walnut shell biochar (WBC)
The higher O/C in WBC1x is consistent with the findings of [14] that the introduction of MgO and Fex Oy contributed to the increase of O% in WBC1x
Summary
The widespread occurrence of phosphate in the aquatic environment due to human activities may pose a threat to the ecosystem [1]. Biological consumption and physico-chemical adsorption methods have been developed to remove the phosphate in aqueous solution [2,3]. The application of chemical precipitation and biological consumption methods are constrained by factors such as substantial investment and maintaining cost, limited application condition, introduction of secondary pollutants [4] and low efficiency due to the less active living organism [5]. The development of a sorption method to remove phosphate that is cost-effective and has a high efficiency, has received increasing research focus. The use of biochar as a cost-efficient adsorbent of organic pollutant has received increasing attention [6]. The use of a powered form of biochar released phosphate into the aqueous solution instead of removing it [7]. Some studies have produced magnetic biochar via impregnation and low-temperature pyrolysis with ferrous chloride and ferric chloride, and magnesium chloride hexahydrate [5,10,11]; the magnetic biochars in some of these studies, comprised of nano-sized
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