# Phosphogypsum Recycling: A Review of Environmental Issues, Current Trends, and Prospects
## 2 Analysis of Trends in Phosphogypsum Use
### Phosphogypsum Recycling in Agriculture
[76] substantiates the expediency of creating X-ray protective structures from composite material based on phosphogypsum. However, the influence mechanisms of composite materials based on phosphogypsum binders require further studies in the field on the efficiency of protection against X-ray and gamma radiation, which also requires further studies [76]. In several studies [77; 78], there was a focus on using phosphogypsum for remediation of contaminated soils (after oil pollution, for remediation of soils contaminated with fuel oil). There is a well-known method for remediation of oil-contaminated soils or soils in the elimination area of oil pollution, characterized by the fact that contaminated soil is not removed, and ameliorants are applied to the soil based on a mixture of phosphogypsum; sand; humus; and mineral fertilizers from nitrogen, phosphorus, and potassium with subsequent ploughing and sowing of crops. It is one of the directions for using phosphogypsum in environmental protection technologies. A mechanical action (ploughing and application of phosphogypsum) mixes the layers. In this case, soil particles saturated with oil will interact with intact soil particles, reducing the pressure of contamination on the substrate. Further decomposition of the organic component of oil will take place under conditions of acidic reaction preservation. Moreover, the redox potential (RP) will be rebalanced, and the reaction of soil respiration will be restored. Finally, the soil uptake of CO2 and its intoxication will be reduced [77]. Automorphic soils are characterized by high levels of RP (550-750 mV in podzols, 400-600 mV in chernozems, 350-450 mV in gray soils). Irrigation reduces RP. In hydromorphic soils, RP is subject to strong seasonal fluctuations and, when the soil is moistened, its level is significantly reduced. Values of RP below 200 mV correspond to cutting and restoration conditions in which the processes of transformation take place and restored forms of iron and manganese compounds, sulfites, and nitrites are formed. Accumulation of the latter has a toxic effect on most cultivated plants. Grape plant is highly sensitive to changes in oxidation-reduction conditions and, at RP below 300 mV, it suffers from chlorosis. There is a possibility to use phosphogypsum in the reclamation of drilling cuttings, which are accumulated and stored directly at the drilling site [78; 79]. Drilling cuttings are characterized by adverse chemical properties: under wet conditions, they swell and become viscous and sticky, whereas under dry conditions, they are characterized by cohesion and hardness owing to the Na content in the absorbing complex. Drilling cuttings also have high alkalinity, and pH of 8.68-9.10, which affects plants [79]. For improvement of physical and chemical properties of drilling cuttings, it is necessary to displace the absorbed sodium by calcium; for this purpose, coagulants are used, among which the use of phosphogypsum is very demanded. This is because phosphogypsum, which is a waste product, is much cheaper than gypsum and has higher solubility, and the presence of water-soluble phosphorus in it enhances the reclamation effect [78; 79]. It is important to consider the processes of using phosphogypsum with the help of biotechnological methods, which gives grounds to substantiate the possibility of conversion of phosphogypsum components of various groups of microorganisms in environmental protection technologies. Thus, bioremediation can be used as one of the phosphogypsum management strategies. It is based on the use of living organisms, in particular, microorganisms, to decompose or detoxify an environmental pollutant as a safe and inexpensive alternative [80]. Different groups of microorganisms can be involved under these bioprocesses. Thus, the presence of autochthonous microorganisms in the phosphogypsum accumulated in the dump, in particular, bacteria capable of recovering radioactive elements and heavy metals, oxidation, and reduction of sulfates, was determined.