Preparation of high‐strength gypsum by crystal regulation of phosphogypsum in nitrate solution

Abstract Phosphogypsum (PG) suffers from impurities and low resource utilization, posing significant environmental challenges and negatively impacting the phosphorus chemical industry. Herein, the technique that combines flotation for PG purification with the conversion of the purified PG into high‐strength gypsum using a magnesium nitrate (Mg(NO 3 ) 2 ) solution under atmospheric conditions was investigated. A “reverse‐direct” flotation successfully removed organic matter and quartz from PG, making it be an ideal secondary resource. The purified PG achieved a whiteness of 55.4%, and a CaSO 4 ·2H 2 O content of 96.57%, meeting the specifications for first‐grade PG outlined in the GB/T 23456‐2018 standard. Mg(NO 3 ) 2 was found to facilitate the conversion of the PG, and glutaric acid (GA) modified the morphology of the high‐strength gypsum. The optimum conditions for high‐strength gypsum with excellent mechanical property were conducted at temperature—85°C, PG fraction—15 wt%, and Mg(NO 3 ) 2 concentration—30 wt%, resulting in an average length of 28.6 µm and aspect ratio of 2.0. The mechanism was that GA selective adsorbed on the end faces of hemihydrate gypsum, inhibiting the crystal growth along the c ‐axis. By supplementing appropriate amounts of Mg(NO 3 ) 2 and of GA in each cycle, the sustainable recycling of filtrate was achieved. Such technology enables the clean production and high‐value utilization of PG.