Environmental assessment of phosphogypsum: A comprehensive geochemical modeling and leaching behavior study

Understanding the variations in the geochemical composition of phosphogypsum (PG) destined for storage or valorization is crucial for assessing the safety and operational efficacy of waste management. The present study aimed to investigate the environmental behavior of PG using different leaching tests and to evaluate its geochemical behavior using geochemical modeling. Regarding the chemical characterization, the PG samples were predominantly composed of Ca (23.03-23.35 wt%), S (17.65-17.71 wt%), and Si (0.75-0.82 wt%). Mineralogically, the PG samples were primarily composed of gypsum (94.2-95.9 wt%) and quartz (1.67-1.76 wt%). Moreover, the automated mineralogy revealed the presence of apatite, fluorine and malladrite phases. The overall findings of the leaching tests showed that PG could be considered as non-hazardous material according to US Environmental Protection Agency limitations. However, a high leachability of elements at a L/S of 2 under acidic conditions ([Ca] = 166.52-199.87 mg/L, [S] = 207.9-233.59 mg/L, [F] = 248.62-286.65 mg/L) is observed. The weathering cell test revealed a considerable cumulative concentration over 90 days indicating potential adverse effects on the nearby environment (S: 8000 mg/kg, F: 3000 mg/kg, P: 700 mg/kg). Based on these results, it could be estimated that the surface storage of PG could have a serious impact on the environment. In this context, a simulation model was developed based on weathering cell results showed encouraging results for treating PG leachate using CaO before its disposal. Additionally, PHREEQC was used to analyze the speciation of major elements and calculate mineral phase saturation indices in PG leaching solutions. The findings revealed pH-dependent speciation for Ca, S, P, and F. The study identified gypsum, anhydrite, and bassanite as the key phases governing the dissolution of these elements.

Exploring the potential reuse of phosphogypsum: A waste or a resource?

Phosphogypsum (PG), the main industrial by-product of phosphate fertilizer industry, primarily consists of calcium sulfate dihydrate. However, it contains various impurities with variable quantities depending on the origin of the phosphate rock. These impurities can restrict the reuse of phosphogypsum as a secondary primary resource. Consequently, large quantities of produced PG are stored in surface stockpiles that occupy extensive land areas and may pose a significant risk of ecological contamination to the surroundings. Researchers have shown growing interest in addressing the worldwide accumulation of this waste material. To gain a comprehensive understanding of the environmental impact of phosphogypsum, it is crucial to explore its properties (e.g., chemistry, mineralogy, radioactivity), and how it interacts with the surrounding environment, enabling well-informed decisions decision regarding its management and its valorization. In this review, we will i) explore the chemical, radiological and mineralogical characteristics of PG; ii) discuss the environmental concerns related to land discharge and sea disposal; and iii) examine the latest advancements in various valorization techniques developed including agriculture, REE extraction, environmental application, chemical and thermal transformation, and also construction sector. Outlining their limitations and challenges restrict in the global variability of phosphogypsum (PG), technical and economic limitations, and the potential for secondary pollution in select valorization approaches. This requires a thorough assessment and comparison with conventional disposal alternatives.