Abstract
Organic acids produced by soil microorganisms can be useful to promote the release of potassium (K) from potassium mineral rocks (KR), but the complexity of low reactivity minerals limits K solubilization and their use as fertilizer. Here, we investigate the ways that different organic acids (gluconic, oxalic, and citric) can affect the solubilization of potassium minerals, in order to propose process strategies to improve their solubility. For this, evaluations were performed using the model minerals KRpolyhalite (sedimentary mineral), KRfeldspar (igneous mineral), and KCl (commercial fertilizer). For KCl and KRpolyhalite, complete solubilization was achieved using all the organic acids, while for KRfeldspar, the highest K+ solubilization (34.86mg L-1) was achieved with oxalic acid. The solubility of KRfeldspar was further investigated under submerged cultivation with the filamentous fungus Aspergillus niger, as well as after a mechanochemical grinding treatment. The biotechnological route resulted in solubilized K up to 63.2mg L-1. The mechanochemical route, on the other hand, increased the release of K by about 8.6 times (993mg L-1) compared to the natural mineral, due to the greater fragmentation of the particles after the treatment (with a surface area about 2.5 times higher than for the in natura KRfeldspar). These findings demonstrated the potential of applying biotechnological and mechanochemical routes with organic acids to improve the solubilization of K present in low reactivity mineral rocks, indicating the possible use of these minerals in more sustainable agricultural practices.
Highlights
The potential of microorganisms to solubilize low solubility mineral rocks for application as fertilizers has been explored by applying the microorganism together with the mineral in the soil, as well as in vitro using microbial cultivation techniques to promote solubilization [1,2,3]
In the present work we investigated the effects of different organic acids on the solubilization of potassium rocks in order to develop strategies to improve the solubility of low reactivity potassium minerals
The results showed that the type of organic acid affected the extent of solubilization of low reactivity potassium rocks
Summary
The potential of microorganisms to solubilize low solubility mineral rocks for application as fertilizers has been explored by applying the microorganism together with the mineral in the soil, as well as in vitro using microbial cultivation techniques to promote solubilization [1,2,3]. The organic acids act directly in increasing the acidity of the medium, where the carboxyl and hydroxyl groups are responsible for chelating the metals present in the mineral and release of nutrients [8] Another important factor that affects the solubilization process is the particle size of the minerals [9, 10]. Knowledge about the effect of organic acids and properties of the mineral rock are essential to improve the nutrient solubilization process, especially for low reactivity potassium minerals
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