A Novel Process to Recover Gypsum from Phosphogypsum

A Review of Fluoride Removal from Phosphorous Gypsum: A Quantitative Analysis via a Machine Learning Approach

This review comprehensively explores fluoride removal from phosphogypsum, focusing on its composition, fluorine-containing compounds, characterization methods, and defluorination techniques. It initially outlines the elemental composition of phosphogypsum prevalent in major production regions and infers the presence of fluorine compounds based on these constituents. The study highlights X-ray photoelectron spectroscopy (XPS) as a pivotal method for characterizing fluorine compounds, emphasizing its capability to determine precise binding energies essential for identifying various fluorine species. Additionally, the first-principle density functional theory (DFT) is employed to estimate binding energies of different fluorine-containing compounds. Significant correlations are observed between the total atomic energy of binary fluorides (e.g., of alkali metals, earth metals, and boron group metals) and XPS binding energies. However, for complex compounds like calcium fluorophosphate, correlations with the calculated average atomic total energy are less direct. The review categorizes defluorination methods applied to phosphogypsum as physical, chemical, thermal, and thermal-combined processes, respectively. It introduces neural network machine learning (ML) technology to quantitatively analyze and optimize reported defluorination strategies. Simulation results indicate potential optimizations based on quantitative analyses of process conditions reported in the literature. This review provides a systematic approach to understanding the phosphogypsum composition, fluorine speciation, analytical methodologies, and effective defluorination strategies. The attempts of adopting DFT simulation and quantitative analysis using ML in optimization underscore its potential and feasibility in advancing the industrial phosphogypsum defluorination process.

Process Optimization and Mechanism Study for Sulfur Recovery from High-Silica Phosphogypsum via Carbothermal Reduction Smelting

Phosphogypsum produced from wet-processed phosphoric acid mainly consists of calcium sulfate dihydrate, which is an important sulfur resource. The traditional sulfuric acid and cement process based on phosphogypsum suffers from unstable cement quality owing to impurities such as phosphorus and fluorine and kiln ringing caused by the low-melting phase. This study investigated sulfur recovery and value-added utilization of liquid slag from high-silica phosphogypsum via carbothermal reduction smelting. A phosphogypsum ingredient (PGI) system was constructed by adding appropriate amounts of silica, alumina, magnesium oxides, and iron oxides to meet the production requirements of slag wool. Carbothermal reduction smelting experiments suggested that the temperature and C/S molar ratio significantly affected the desulfurization rate and phase structure of the slag. More than 97.44 wt % of sulfur could be recovered with a C/S molar ratio of 0.5-0.8 at 1300 °C or above in the molten state, and the molten slag was an amorphous magnesium-calcium-aluminosilicate. The PGI desulfurization mechanism is discussed based on the phase transformation and slag microstructure evolution.

Future Trends in Advanced Materials and Processes

The main objective of this Special Issue was to publish original high-quality research papers covering the most recent advances in materials properties, as well as comprehensive reviews addressing the relevant state-of-the-art topics in the area of materials processing, with relevant practical applications [...].

Potential uses of phosphogypsum: A review

Phosphogypsum (PG) is a by-product of the phosphate fertilizer industry that is produced during the phosphoric acid production process. Annual global PG production ranges between 100 to 300 Mt, with only 15% of that utilized while the rest is usually placed on large dumps with potential serious human and environmental impacts. The aim of this study is to give an overview and to evaluate the existing and potential uses of PG that extend from soil stabilization to cement and chemical industry and for agricultural to geotechnical, human impacts, and environmental applications. More specifically, PG can be used as a substitute in the cement industry, in building materials and in road construction, as a fertilizer for soil improvement, as a raw material for the production of some chemicals, and as a backfilling material for the rehabilitation of abandoned mines and quarries, while the recovery of gypsum and the extraction of rare earth elements signifies the potential importance of PG to cyclic economy. The paper offers an extensive overview of existing and potential uses of PG, discusses their adequacy, and reveals that PG can be widely used under certain conditions, rather than disposed as waste in stockpiles.