Utilization of industrial by-product gypsum to prepare urea gypsum cocrystals as a sustained release fertilizer: A review

The large-scale accumulation of industrial by-product gypsum has led to land embezzlement and serious environmental pollution. Meanwhile, as a predominantly used nitrogen fertilizer, urea shows a disadvantage of high solubility in soil. Therefore, it can hydrolyze into large amounts of ammonium salts so rapidly that cannot be absorbed efficiently by crops. The sustainable method of using industrial by-product gypsum to synthesize urea gypsum cocrystals is a promising way to solve above challenges. The synthesized urea gypsum shows low aqueous solubility and hygroscopicity, which can be used as sustained release fertilizer. In this review, the present status regarding urea gypsum is systematically reviewed, including its development history, preparation methods, impact of different raw materials, evaluation of products performance, and large-scale trials. This review aims to reveal the current situation, identify current gaps, and provide suggestions for future investigations concerning urea gypsum.