Reaction parameter optimization of ammonium sulfate production from phosphogypsum

Phosphogypsum (PG), by-product of wet process phosphoric acid production, has a high recycle and reuse potential within the scope of compliance with CE strategies. This study offers a straightforward, two-step solid/liquid heterogenous reaction sequence, providing the conversion of PG to ammonium sulfate (AS). Experiments were conducted in accordance with the OFAT design matrix with 3 factors, namely solid/liquid (w/v) ratio, pH, and particle size. Highest PG to AS conversion was achieved as 54.55% by utilizing PG below 125 ?m particle size in the reaction performed with 1/10 solid/liquid (w/v) ratio at pH 10. Nitrogen and sulfur content of AS samples were characterized by Dumas Method and gravimetric SO4 (ISO 9280:1990) analysis, respectively. The elemental composition was determined by ICP-OES, the crystallographic structure was investigated by XRD analysis, and the surface morphology of the particles obtained in the reaction was examined by SEM analysis. Chemical composition of AS product obtained at these conditions was determined as 21.29 wt% nitrogen and 24.23 wt% sulfur, respectively; where theoretical nitrogen and sulfur content in AS is 21.21 wt% and 24.24 wt%, respectively. Outputs provided from this study have industrial importance since it proposes a novel approach for effective waste valorization and a new insight to AS production in current fertilizer shortage.