Valorization of Acidic Soapstock Wastewater and Phosphorite Mining Waste to Produce a Phosphorus-Containing Fertilizer Precursor: Effect of the AWW:MM Mass Ratio
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1
Urgench State University named after Abu Rayhan Biruni
2
Karshi State Technical University
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ABSTRACT
The vegetable oil industry produces an acidic waste stream in soapstock acid splitting, and the phosphorite mineral dressing processes generate low-grade mineralized mass (MM), which is not easy to process in a traditional way. This research paper investigates the possibility of their co-treatment through wet neutralization and the effect of the acidic soapstock wastewater-to-mineralized mass (AWW:MM) ratio on this process. AWW (pH = 2.0) and MM (total P₂O₅ = 15.09%, CaO = 43.17% and CO₂ = 14.01%) were mixed in the mass ratios of 100:10-100:40, treated at 60 °C for 30 minutes at 500 rpm and then dried at 80 °C to a level of 14% residual moisture. The ratio analyses were carried out in triplicate (n=3). The results after correction reveal that the total P₂O₅ increased from 8.19% to 12.49%, while the extractable P₂O₅ by 2% citric acid decreased from 3.81% to 2.02% with increasing amounts of MM. According to the screening criterion based on the literature that the citric acid extractable percentage must be more than 25%, ratios of 100:10-100:20 passed the screening criterion; 100:20 was selected as one of the possible compositions since it contained the highest amount of total P₂O₅, 10.42%, among the ratios that met the screening criterion, which included 3.02% citric acid extractable P₂O₅, (28.98% of total) and 2.21% 0.2 M Trilon B extractable P₂O₅ (21.31% of total). The X-ray diffraction (XRD) and Fourier-transform infrared (FTIR) spectra of the dried 100:20 sample indicated a multiphased calcium phosphate/carbonate/sulfate matrix. Hence, the solid can be termed a fertilizer precursor containing phosphorus and not an agriculturally proven fertilizer. Full pot, field, plant uptake, leachability, and complete safety studies are necessary to give agricultural recommendations.