Abstract
Phosphogypsum (PG) and titanium gypsum (TG), as a by-product (solid waste) in phosphate fertilizer and titanium dioxide industry, are causing serious environmental hazards. The resource/harmless application of PG and TG is the development trend in the future. The biological function of red yeast (Rho: Rhodotorula mucilaginosa) can effectively reduce the concentration of pollutants in the environment and has the potential of biological flotation/purification of mineral solid waste. In this study, the bioremediation mechanism and safe utilization efficiency of Rho for different contents of PG and TG were explored by using its biological flotation function. The X-ray fluorescence spectrometry (XRF) results showed that F was the main toxic element in PG and TG, and Pb and Cd did not reach the detection limit. The processing capacity of Rho for PG (>10 g/ml) is higher than that of TG (<5 g/ml). After bioleaching by Rho, the proportion of F in PG and TG solid decreased by 61.45–63.79% and 49.45–59.19%, respectively. The results of three-dimensional fluorescence, extracellular polymeric substance (EPS) extraction, X-ray diffraction (XRD), and scanning electron microscopy (SEM) confirmed that Rho could accelerate the release of harmful elements (F) in PG and TG. SEM showed that Rho cells and secretions adhered and wrapped on PG/TG, causing PG/TG decomposition and fragmentation. In addition, the adsorption of EPS and the formation of Ca5(PO4)3F are two main ways for Rho to remove F. Furthermore, under the condition of high concentration bioleaching, Rho can accelerate the release and utilization of P in PG, which is not only for the re-precipitation of Ca5(PO4)3F but also conducive to the reproduction and utilization of microorganisms. Meanwhile, the purification/safe reuse of PG by Rho is easier than that of TG. Therefore, the toxicity of PG and TG bioleaching by Rho can be greatly reduced, suggesting the huge potential of Rho in soil improvement and remediation.
Highlights
Phosphogypsum (PG) is a complex solid waste produced during the production of phosphate fertilizer and phosphoric acid from the raw phosphate ore using a wet-process treatment (Papastefanou et al, 2006)
ICPOES results showed that the content of Pb, Cd, Zn, and Cu elements was below the detection limit in PG or Titanium gypsum (TG) solution (
This study found that there are three main mechanisms for the resource/safety utilization of solid waste (PG/TG) by red yeast (Rho) bioleaching
Summary
Phosphogypsum (PG) is a complex solid waste produced during the production of phosphate fertilizer and phosphoric acid from the raw phosphate ore using a wet-process treatment (Papastefanou et al, 2006). The main constituents of PG are anhydrous calcium sulfate and massive impurities including phosphate, fluoride, and heavy metals (Hao et al, 2005; Rashad, 2017; Li and Zhang, 2020; Romero-Hermida et al, 2020). Titanium gypsum (TG) is an industrial by-product from the titanium dioxide industry. Due to the complex composition of PG and TG (such as, Pb, F, P, Fe, and Si), discarding/stacking them in large quantities will lead to soil hardening, eutrophication, heavy metal pollution, and other serious environmental pollution problems (Li et al, 2020; Marchi et al, 2020; Costa et al, 2021)
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