# Phosphogypsum Recycling: A Review of Environmental Issues, Current Trends, and Prospects
## 2 Analysis of Trends in Phosphogypsum Use  
Considering the quantities of formed and produced phosphogypsum, the actual problem is not only the phosphogypsum removal, transportation, and storage in waste dumps and sludge collectors, but also its utilization with already developed methods and the development of new methods and more possibilities for its use.  
Based on the number of publications (Figure 1), the interest in phosphogypsum as a source of secondary raw materials has significantly increased over the past decade. Initially, phosphogypsum was considered mainly as a component for construction, cement, road-building, and agricultural industries. However, over the last 10-20 years, given the increasing anthropogenic pressure on the environment and the resulting shortage of natural sources of raw materials, the focus has shifted. Phosphogypsum, which has many useful elements, is thus being considered as a source of calcium, phosphorus, rare-earth elements, and trace elements, among other, as well as a mineral resource in technological processes of environmental protection.  
Figure 1: Publishing trends (number of papers) in the area of phosphogypsum research (using Scopus Database).  
There are various directions and ways for the direct use of phosphogypsum and its processing into other products, which have proven technical feasibility and expediency for the use of phosphogypsum in the national economy instead of traditional raw materials.  
According to the aforementioned properties of phosphogypsum, the field of research is currently (Figure 2) shifting more towards environmental sciences, but engineering research is simultaneously being actively developed. Research in materials science is also being developed owing to the component composition of phosphogypsum (Figure 3).  
Figure 3: The main directions of phosphogypsum recycling.  
Figure 2: Papers in the field of “phosphogypsum” classified by fields (Scopus Database).  
At the same time, the direction of using phosphogypsum in agriculture for fertilization and reclamation of soils, especially saline soils, remains a quite promising direction, owing to the changes in climatic parameters and aridization, with increasing areas of anthropogenic (secondary) saline soils (Figure 3).  
Areas of biotechnology and environmental protection where phosphogypsum is not only applied as a substrate, a carrier of bioculture, but at the same time is used as a substrate that has nourishing value when it comes to phosphogypsum application in technologies based on the microorganisms (for example, off-gas cleaning, wastewater treatment, reclamation of soils contaminated with oil-based products/petroleum products, and drilling cuttings) are becoming relevant and increasingly popular.  
Development in the field of research on the properties and applications of phosphogypsum is taking place in many countries with different levels of economic development, such as in Western Europe, Africa, India, Russia, and especially in China (Figure 4). The use of phosphogypsum as a secondary raw material is in high demand in many countries of the world. Leadership in terms of published papers belongs to China, as a country where the economy is gaining momentum and the use of cheap secondary resources is a very relevant issue, although countries of America and Europe, as well as India and Russia, are also in a tow.  
Considering the nature of Ukraine, as a country with an agrarian component and because of the economic situation, the use of phosphogypsum has shifted the emphasis in recent times. The use of phosphogypsum for road construction has been suspended because of the short duration of the roadway covering and the possibility of harmful components of phosphogypsum getting into the environment. In addition, the use of phosphogypsum in the construction materials and cement industry has been slowed down by the economic crisis.