Mechanism of orthophosphate (PO4-P) adsorption onto different biochars

Joseph Osafo Eduah,Mathias Neumann Andersen,Stephan Weck Henriksen,Eric Kwesi Nartey,Mark Kofi Abekoe

doi:10.1016/j.eti.2019.100572

Joseph Osafo Eduah, Mathias Neumann Andersen + Show 3 more

Open Access

https://doi.org/10.1016/j.eti.2019.100572

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Abstract

Abstract The adsorption mechanisms of phosphate (PO 4 -P) onto cocoa pod husk (CP), corn cob (CC), rice husk (RH) and palm kernel shell (PK) biochar pyrolyzed at 300 °C and 650 °C were investigated. A series of batch experiments were undertaken to assess the effects of contact time and pH. Results show that PO 4 -P adsorption equilibria for the biochar types was within 6–15 h, being rapid in the 300 °C-biochar types. The equilibrium pH for maximum PO 4 -P adsorption varied among biochar types, ranging from of 2.6 to 4.8 and increasing with decreasing PO 4 -P adsorption. Pseudo-second-order and Elovich models explained the adsorption data well indicating a chemisorption process on heterogeneous biochar surface. PO 4 -P adsorption was controlled initially by intraparticle diffusion and subsequently by chemisorption. Per the properties of the biochars (FTIR and elemental composition) and pH (equilibrium pH and Δ pH), PO 4 –P was adsorbed through electrostatic attraction, surface precipitation and ligand exchange, and the relative importance of these processes differed among the biochar types. Biochar types (PK300, PK650, CP300, CP650, RH650 and CC650) that adsorbed PO 4 -P through surface precipitation and ligand exchange reactions can be used to remove PO 4 -P from wastewater since PO 4 -P is strongly adsorbed, controlling PO 4 -P enrichment of water bodies.

Highlights

Adsorption of phosphate (PO4-P) by organic material is of relevance in controlling the transport, mobility and enrichment of PO4-P in aquatic environment
Fourier transform infrared (FTIR) spectrum of corn cob (CC), palm kernel shell (PK), cocoa pod husk (CP) and rice husk (RH) at 300 ◦C and 650 ◦C revealed the information about adsorption process (Fig. 1)
PO4-P adsorption was faster on the low pyrolysis biochar types (300 ◦C) as compared to their counterparts (650 ◦C)

Summary

Introduction

Adsorption of phosphate (PO4-P) by organic material is of relevance in controlling the transport, mobility and enrichment of PO4-P in aquatic environment. PO4-P is an essential nutrient for the growth of plants and other living organisms, it can serve as an environmental pollutant (Dodds et al, 2008; Almeelbi and Bezbaruah, 2012). The increased PO4-P in water bodies as a result of inappropriate and frequent discharge of waste water stimulates excessive growth of phytoplankton and algae which in turn decrease the quality of drinking water (Dodds et al, 2008). In order to reduce the negative effects of overloading water bodies with PO4-P, it is necessary to assess various strategies and to evaluate the PO4-P removal effectiveness of adsorbents that could be exploited for use as waste water cleansing agents of PO4-P ions prior to wastewater discharge into natural water bodies (Biswas et al, 2008).

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