Phosphate minerals as a non-renewable resource come either from marine sediments (75%), from igneous rocks, metamorphic and renewable sediments (15–20%), or from biological sources (2–3%). Consequently, the world's largest phosphate reserves are from sedimentary deposits, which consist mainly of carbonate minerals. Phosphate resources can also be divided into three groups according to P2O5 concentration, the first group is low-grade ore with P2O5 content of 12–16%, the second group is medium-grade ore with P2O5 content of 17–25%, and the last is high-grade ore The ore contains 26–35% P2O5. Whereas, sediments of high economic and commercial value contain 28–38% P2O5 (Rizk, 2021).
Therefore, to increase P2O5 in rocks, a number of methods have been used, including mechanical activation of RP using a rotating chamber vibrating mill. This process significantly increases the chemical reaction with 2% citric acid and neutral ammonium citrate and improves the filtration performance. This is the most efficient intermediate step in the phosphoric acid production of all phosphate fertilizers (Ibrahim et al., 2010).
Since the quality of the main impurities in phosphate rock (PR) is different, the method of extracting phosphate from it is also different according to its source (Ryszko et al., 2023). RW composition is composed of siliceous ore, which contains silica in different forms, such as quartz or chalcedony, which can be extracted by flotation, gravity separation and other techniques. Although clay ores are mainly associated with hydrated iron and aluminum silicates or their oxide impurities, they are obtained by simple enrichment techniques such as scrubbing and washing, but in some cases dispersants are required. While sedimentary rocks containing calcareous compounds such as calcite and/or dolomite with significant amounts and impurities of silica, the separation process by flotation or physical separation methods (traditional techniques) is difficult to perform efficiently, and this is because the physical properties of carbonates and phosphates are very similar. While the rocks contain carbonates in a precise manner in the phosphate particles, separation by physical means becomes impossible (Chen and Graedel, 2015; Kybartiene et al., 2015; Ptáček, 2016).
The bio-decomposition of PR by microorganism's growth depended mainly on some organic acids are produced by the oxidation process that occurs on the outer surface of the plasma membrane of the cell, and this acidic condition is produced in the medium as a reaction product. In this case, it is beneficial to the growth of bacteria, the continuous oxidation of pyrite and the leaching of phosphorus from phosphate rock. Organic acid production including citric, oxalic, malonic, butyric, malic, lactic, acetic, succinic, gluconic, glyconic, adipic, fumaric, and 2-ketogluconic acid is one of the microorganism’s mechanisms to dissolve rock phosphate is pyrites bioleaching. Other mechanisms include its oxidation by bacteria to produce H2SO4 and FeSO4. RP is dissolved by H2SO4 to form soluble phosphorus compounds. Fe2+ in FeSO4 is oxidized to Fe3+, providing energy for bacterial growth (Chi et al., 2006; Chi Ru-an, et al., 2007; Othman, and Panhwar 2014), and acid and alkaline phosphatases activities. Phosphatases eliminate phosphorus from their substrates by hydrolyzing phosphate monoesters into phosphorus ions and molecules with free hydroxyl groups (Othman, and Panhwar 2014). As shown by (Hamdali et al., 2010), the concentration of soluble phosphorus increased significantly during the stationary phase of the culture medium of Streptococcus strains. This is related to the sequential appearance of two strong ion chelators disrupting the hydroxyapatite structure, leading to the release of soluble phosphorus, as well as the accumulation of intracellular storage polymers such as glycogen and polyphosphates. So, that this strains was able to release P from RP but consumed it as soon as it was released.
Therefore, this study aimed to evaluate and improve the biological activity and growth status of Streptomyces and its effect on bio-beneficiation of RW.