**5. Conclusion**

structural incorporation of pollutants by co‐precipitation and dissolution/precipitation

Aluminosilicates, primarily clay minerals, and zeolites are inorganic ion‐exchangers with high surface area, which have been conventionally used for water treatment processes, for the treatment of liquid nuclear waste, and for the protection against nuclear waste leaking [79– 90]. Natural zeolites are the framework aluminosilicates, with variable porosity due to which they can selectively capture the ions having an appropriate radius. Zeolites are excellent sorbents of fission products that otherwise exhibit very low affinity for sorption on solid surfaces (such as Cs and Sr isotopes [78, 80]. Clay minerals (montmorillonite, vermiculite) are layered aluminosilicates, in which ion‐exchange is typically associated with cations situated

soils was tested using different synthetic and natural zeolites [91]. With the addition rate of

was observed, as well as the significant changes in cationic composition and pH of the soil. By comparing the effect of various materials onto Sr2+ immobilization in the soil, zeolite has been identified as the most efficient, followed by bone char, synthetic hydroxyapatite, and phos‐ phate rock [92]. The most of the results have been obtained on the laboratory level or out of small‐scale field applications, while in solving the actual problems of soil contamination,

The other promising group of materials is the phosphate group. Among different soluble and sparingly soluble phosphate bearing materials, hydroxyapatite (Ca10(PO4)6(OH)2, HAP) exhibited superior physicochemical and sorption properties, that is, low solubility in water, high specific surface area, high buffering capacity, and the high sorption capacities towards variety of cationic and anionic pollutants [93]. HAP is by far the most selective to U and Pb, due to the removal mechanism which involve dissolution of HAP and precipitation of thermodynamically more stable Pb and U containing phases [87, 94]. In soil, apatite matrices were highly effective for U uptake; however, the increase of organic matter content influenced the decrease of amendments efficiency [95]. Furthermore, the selectivity and capacity of HAP towards Pu, Co, Ni is very high, moderate for Sr, while low considering Cs and Tc [78, 81–84,

Comparing different apatite forms (synthetic, mineral, and biogenic), the product extracted

metal concentrations, poor crystallinity, and high microporosity necessary for optimal performance in the field [87]. Giving that this sorbent is produced from the commercial fish industry waste, it is both environmental friendly and cost‐effective for large‐scale operations. However, the bioavailability of essential trace elements was found to decrease at high HAP addition rates (5%), while uptake of As by plants was found to increase after HA treatment [96]. These results demonstrate that HAP application for the remediation of contaminated soil

In addition to animal bones as the source material for apatite production, many other industrial by‐products, wastes, and recycled materials are being tested as potential soil additives [65, 72]. In order to preserve natural mineral resources and reduce the costs of the immobilization

from fish bones exhibited the best sorption properties, due to CO3

and Sr2+ contamination in the sandy

and 24.5 for Sr2+ions,

2− substitutions, low trace

in clay mineral interlayers [72]. The stabilization of Cs+

266 Soil Contamination - Current Consequences and Further Solutions

1%, the maximum reduction of soil‐to‐plant transfer factor of 12.5 for Cs+

applications are generally connected with Chernobyl and Fukushima disasters.

processes).

86–88].

must be optimized and controlled.

The source term and a wide variety of soil and environmental parameters affect the radionu‐ clide behavior in terrestrial systems. Weaker bonds between the pollutant and soil components implicate higher mobility of pollutant, higher potential to get into the solution and to be adopted by the biota. In addition to total concentration of the pollutant, understanding of its environmental behavior by determining distribution pattern in different fractions of the soil is of principal importance for the selection of optimal remediation technologies. Due to the large number of factors that affect the outcome of the soil rehabilitation process, selection of optimal solution must be done on a case‐by‐case basis. Still, some guiding principles can be derived from the research studies and the practical experience: pollutants mainly bonded in exchangeable, carbonate and reducible phase are suitable for chemical extraction, while removal of contaminants from organic and residual fraction is neither economical nor feasible. Optimization of extracting solution composition, pH, the time, and the mode of the interaction with the soil are the perspective fields of research which must include the type of the soil and the radionuclide, and the effects of the extracting solution to other important soil characteris‐ tics. Analyzing the contamination level, the size and the properties of contaminated area, *in situ* soil immobilization may prove to be more suitable solution which permanently increases sorption capacity of the soil. The use of mineral‐based amendments as soil remediation additives should be as much as possible substituted by appropriate waste materials and by‐ products, which environmental compatibility, selectivity, and long‐term effectiveness, must be verified on a variety of soil types. Immobilization technologies may be particularly useful if applied in combination with conventional *ex situ* (soil removal, chemical extraction) or *in situ* technologies (bioremediation, phytoremediation, reactive barriers, capping, monitored natural attenuation), for the stabilization of the residual activity.
