Rock phosphate solubilization by abiotic and fungal-produced oxalic acid: reaction parameters and bioleaching potential.

Gilberto De Oliveira Mendes,Laszlo Csetenyi,Thomas Dyer,Geoffrey Michael Gadd

doi:10.1111/1751-7915.13792

Gilberto De Oliveira Mendes, Laszlo Csetenyi + Show 2 more

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https://doi.org/10.1111/1751-7915.13792

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Abstract

SummaryOxalic acid‐producing fungi play an important role in biogeochemical transformations of rocks and minerals and possess biotechnological potential for extraction of valuable elements from primary or waste ores and other solid matrices. This research investigates the extraction of phosphate from rock phosphate (RP) by oxalic acid. Reaction parameters were derived using pure oxalic acid solutions to solubilize RP. It was found that the oxalic acid concentration was the main factor driving reaction kinetics. Excess oxalic acid could retard the reaction due to calcium oxalate encrustation on RP surfaces. However, complete P extraction was reached at stoichiometric proportions of apatite and oxalic acid. This reaction reached completion after 168 h, although most of the P (up to 75%) was released in less than 1 h. Most of the Ca released from the apatite formed sparingly soluble calcium oxalate minerals, with a predominance of whewellite over weddellite. Bioleaching of RP employing biomass‐free spent culture filtrates containing oxalic acid (100 mM) produced by Aspergillus niger extracted ~ 74% of the P contained in the RP. These findings contribute to a better understanding of the reaction between apatite and oxalic acid and provide insights for potential applications of this process for biotechnological production of phosphate fertilizer.

Highlights

SummaryOxalic acid-producing fungi play an important role in biogeochemical transformations of rocks and minerals and possess biotechnological potential for extraction of valuable elements from primary or waste ores and other solid matrices
This research describes a process for rock phosphate (RP) solubilization employing oxalic acid
Up to 100% P was extracted from RP by oxalic acid when stoichiometric proportions of apatite and oxalic acid (1 Ca10(PO4)6F2:10 H2C2O4) were reacted, which means that an excess of oxalic acid was not required to complete the reaction

Summary

Introduction

Oxalic acid-producing fungi play an important role in biogeochemical transformations of rocks and minerals and possess biotechnological potential for extraction of valuable elements from primary or waste ores and other solid matrices. This research investigates the extraction of phosphate from rock phosphate (RP) by oxalic acid. Complete P extraction was reached at Global food demand is increasing rapidly, with some forecasts indicating the need to double agricultural output from 2005 to 2050 (Alexandratos and Bruinsma, 2012). One of the main components required to increase crop yields is fertilization, and this will probably result in increasing fertilizer consumption from 166 Mt in 2005 to 263 Mt in 2050 (Alexandratos and Bruinsma, 2012). Unlike nitrogen-containing fertilizers which are derived from atmospheric N2 through biological or industrial fixation, phosphate fertilizers are obtained mainly from non-renewable mineral deposits, primarily rock phosphates (RPs). The depletion of RP reserves is concerning and the subject of a vigorous debate since there is a consensus that sustainable P use is paramount for global food security (Cordell et al, 2009; Schroder et al, 2010; Cordell and White, 2011; Withers et al, 2015)

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