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The New Conception of Radiological Sustainability Possibilities by Reutilization of Residues Products and Building Materials

by
Amin Shahrokhi
*,
Lordford Tettey-Larbi
,
Esther Osei Akuo-ko
,
Edit Tóth-Bodrogi
and
Tibor Kovács
Department of Radiochemistry and Radioecology, Research Centre for Biochemical, Environmental and Chemical Engineering, University of Pannonia, 8200 Veszprém, Hungary
*
Author to whom correspondence should be addressed.
Sustainability 2023, 15(13), 10647; https://doi.org/10.3390/su151310647
Submission received: 6 April 2023 / Revised: 26 June 2023 / Accepted: 26 June 2023 / Published: 6 July 2023
(This article belongs to the Section Environmental Sustainability and Applications)
Browse Figure
Versions Notes

Abstract

:
The concept of radiological sustainability has been reviewed using the possibility of the reutilization of NORMs regarding the 2050 sustainable development concepts. This study is reviewing the capability of re-production of NORM residues based on their properties and the applicable treatment before reutilization. Linking the waste producers and construction materials industry as mineral end-users could contribute to the creation of industrial symbiosis and result in waste reduction and preserving natural resources on one hand, and CO2 reducing and energy saving on the other hand. According to EU-BSS (European Basic Safety Standards Directive), the characterization of NORMs as a secondary raw material for use as construction materials is necessary, however as an additive or secondary material their radiological behavior and material properties are quite important regardless of their origin. This is to say that the reutilization of NORM residues provides a better financial and environmental solution while reducing possible radiological effects on humans. NORM residue or waste could become a high material resource for the cement industry. In this regard, the assessment of radium equivalents (Raeq) and external and internal indexes (I-indexes) are useful tools to classify NORM residues before their inclusion in building products. This assessment and/or indexes reflect the risk of external exposure much better than the specific activity concentration of Ra-226, Th-232 and K-40. Equally, building material properties such as density and thickness should be taken into consideration when designing building materials that contain NORM residue. Furthermore, mixtures or additives of NORM residues are proven to result in the reduction of activity concentration in the raw residue with other raw materials, and this offers flexible reuse options depending on the final product. By integrating radiological considerations into sustainable development initiatives, we can work towards a safer, healthier and more sustainable future.

1. Introduction

All minerals and raw materials of terrestrial origin contain some radioactive materials from human and natural sources, among which 238U, 232Th and 40K can be mentioned as the most important ones from the point of view of radiation protection.
Generally speaking, for radiological sustainability, recycling or reutilization of residue or by-products which contain NORMs, rather than disposing of them as waste, is the first consideration to achieve the re-utilization of materials in building materials and the aim of radiological sustainability. The importance of using by-products and residues has increased in recent decades due to the reduction of environmental pollutants and the achievement of sustainability in the human environment. Besides, the use of residues sometimes provides better financial solutions. It seems that in this regard, the construction materials industry is a suitable option, as residual materials and waste materials have been used in the construction industry for a long time [1,2,3,4,5,6]. The use of certain mining by-products such as waste rock also has a past [5,7]. Therefore, it can be concluded that there are potential opportunities for the reutilization of NORM residues or the opportunities for safe use of NORM residues as an additive or even raw material in the building materials industry, though in some cases they might be treated before reuse. The use of other wastes containing NORMs, e.g., coal slag and fly-ash, have become frequent after the development of cement production [8,9]. However, the use of these by-products has to be restricted in several cases, as on the one hand, waste impairs the structural properties of the end-product [10,11], and on the other hand, different contaminants will have dissolved and entered the environment, causing harm to the environment or to human health [12].
Radiological sustainability can be linked to several United Nations (UN) Sustainable Development Goals (SDGs) due to its impact on human health, the environment and sustainable practices. While radiological sustainability is not explicitly mentioned as a standalone goal, it is closely related to several SDGs, including goals 3, 11, 12 and 17.
Radiological sustainability refers to the concept of achieving a balance between the utilization of radiation and radioactive materials for various purposes, and minimizing their potential adverse impacts on human health, the environment and future generations. It encompasses principles, practices and strategies that promote the responsible and safe use of radiation across different sectors.
The goal of radiological sustainability is to ensure the long-term viability and effectiveness of radiation-related activities while protecting human health and the environment. It involves considering the entire life cycle of radiation sources, from their production and use to their disposal and the management of associated wastes.
In fact, one of the key concepts of radiological sustainability is that of “Resource Optimization: using strategies such as recycling, reusing and minimizing waste generation”, applicable by exploring alternative technologies and practices that reduce reliance on radioactive materials or optimize their use. This is also part of resource optimization to develop a new strategy for NORMs residues reutilization, while balancing the benefits of the reutilization of residues with the protection of human health and the environment.
The development in radiological sustainability, a new strategy for NORM reutilization, should be guided by the need for keeping radiation risks as low as reasonably achievable. Regarding the reusing of by-product and residue containing NORM in building materials, it should be considered that the quantity and quality of additives usable in building materials has long been set out by strict regulations. The radioactivity of materials used in building materials is regulated explicitly by the standards of only relatively few countries. An example of using NORMs in building materials is cement. Cement production lines consume an extensive amount of energy, and are also a carbon-intensive industry. Ordinary Portland cement (OPC) is one of the most important materials since it is a key constituent of concrete, which is the world’s most consumed man-made material. As such, it is considered as the third-largest source of CO2 emissions, and with increasing cement demand, it is expected that emissions of CO2 related to cement manufacture and use will double by the middle of this century. This cement can be prepared by using substantial amounts of diverse industrial residues (e.g., coal fly ash, bottom ash and red mud), and hence the natural resources could also be preserved. NORM waste could represent high secondary mineral resource potential in the cement industry. Red mud is a NORM waste, and is the main waste generated in aluminum and alumina production. Due to high alkalinity and trace metal content, the disposal of large quantities of red mud causes serious environmental problems such as soil contamination, groundwater pollution, etc. Another NORM waste which is of great concern is bottom ash, which is still disposed. Consequently, larger quantities of red mud and bottom ash are not used in any form and are still stored, leading to a series of environmental pollution problems. One of the economic ways is using red mud and bottom ash in cement production, with the incorporation of these NORM wastes in belite-calcium sulfoaluminate cement, though the reutilization of NORMs in the natural radionuclide content of construction products contributes to natural background radiation in two ways: (1) The gamma radiation of the primordial radionuclides (40K; and daughter elements of 238U, 232Th) increases the external gamma dose rate; and (2) inhaled radon (222Rn), thoron (220Rn) and their progenies augment the risk of the evolution of pulmonary cancer [13]. Due to the radioactive character of bottom ash and red mud, the complex radiological risk assessment analyses and the long-term effects of their application are important factors to assume the amount of human radiation exposure and environmental impact. Radiological assessment of natural radioactivity of building materials containing different NORM wastes (red mud, bottom ash, fly ash) was already studied, and it is known that some wastes can cause an increase in the activity levels of natural radionuclides. Sanjuan et al. studied ground coal bottom ash as a potential portland cement constituent and concluded that despite the increased activity concentration index, bottom ash can be used in building materials. Red mud as a partial replacement of Portland cement was also studied in terms of radioactivity, and the results showed that the materials’ radioactivity was also increased.
With the expansion of the concept of sustainable development, deep understanding and attention in the field of radiological sustainability is missing. The lack of extensive research in this field, for recovering existing natural resources in the form of NORM wastes to be part of the sustainability in the construction materials, comes to slow down. This paper tries to review the possibility of reusing NORMS to be a turning point in the definition of radiological sustainable development. This paper tries to review the possibility of reusing NORMS to be a turning point in the definition of reutilization of NORMs residues in the Resource Optimization aspect key of radiological sustainable development, while considering the potential radiological hazards associated with building materials and making informed choices to minimize any risks to occupants and the environment.

2. Materials and Methods

2.1. Data Acquisition

Data collection was carried out to extract the needed information regarding NORMs activity concentrations in building materials of different categories from published articles. The categories included raw materials, NORM-containing building materials and by-products. This work also focused on some specific by-products recognized by the EU-BSS as possible building materials. These included red mud, fly ash, bottom ash, manganese clay, blast furnace slag, bauxite quarry waste, limestone, gypsum, slag and ilmenite mud. They are also considered non-residue or industrial by-products. Information was extracted from peer-reviewed journals published articles, conference proceedings, technical reports and literature available in the English language relevant to the topic only within the last 10 years (2012–2022). Therefore, articles were searched primarily from electronic sources, focusing on popular publishers such as Springer Nature, Elsevier, MDPI, De Gruyter and Wiley. Beside the direct access to some open access publishers like MDPI, to extend our search range and gather relevant articles, trusted academic databases and search engines such as PubMed, IEEE Xplore, ResearchGate, Google Scholar, ScienceDirect and DOAJ were also utilized. Appropriate keywords like “NORM4BUILDING”, “NORM residue”, “NORM by-products”, “NORM concentration”, “radiological hazard index”, “NORM reusability”, “ NORM in mining“, “Radioactive by products” and “NORM residue management” were employed during the search process (words such as red mud, fly ash, bottom ash, manganese clay, blast furnace slag, bauxite quarry waste, limestone, gypsum, slag, ilmenite mud, radiation, reutilization and reusing also were employed). Documents from UNSCEAR, ICRP and IAEA were also sourced for this work.
Further screening was done to adhere to the aim and scope of the present review by inclusion/exclusion of (noting that the duplicated studies has not been considered during selection process and not counted):
  • studies with NORM residues used in concrete were included;
  • studies with proportionate inclusion on NORM residue in cement were included;
  • studies with possible means of reducing the activity concentration in NORM residue were included;
  • studies with radium equivalent results were excluded;
  • studies with only radon and thoron indices were excluded;
  • studies lacking the proper description of methods employed were excluded to avoid the misinterpretation of the results and misleading conclusions; and
  • studies missing the details of the location of the investigation were ignored.
During conducting a review on papers, several limitations could be faced, such as the comprehensiveness and representativeness of the review, heterogeneity of studies (Radiological sustainability encompasses various aspects, such as radiation protection, waste management and resource optimization) and quality assessment.
Following a careful review of the title and abstract, after ruling out the studies as per the exclusion criteria, the logical search yielded a total of 59 of 110 relevant journal articles to be considered for the systematic review, with the results meticulously documented in the following sections. Figure 1 shows the flow for the data acquisition and selection.
After filtering the documents, the activity concentrations of NORMs in building materials and their radiological indices were extracted for analysis. This includes the assessment of the radiological concentrations in NORM residues from different countries, and their corresponding radiological hazard indices for determining the screening criteria for inclusion in building materials. The activity concentrations and radiological indices of the investigated building materials were presented as a mean value. The results of the analyses were presented as activity concentration of 226Ra, 232Th, 40K, external hazard index, gamma index, absorbed dose rate and annual effective dose.

2.2. Categorization of Building Materials with Frequently Used Radiological Indices

2.2.1. Gamma Index (Activity Concentration Index)

According to EU-BSS (the European Council Directive (2013)/59/Euratom), the level of indoor external exposure to gamma radiation emitted by building materials should be less than 1 mSv/y. In addition, the directive proposed the Activity Concentration Index (I) as a conservative screening tool for identifying building materials that may exceed this level. The I is calculated as follows [14,15,16,17].
Iγ = (ARa/300) + (ATh/200) + (AK/3000)
where ARa, ATh, and AK are the activity concentrations of 226Ra, 232Th, and 40K, respectively (Bq/kg). The reference value for the gamma index for building materials is 1, which corresponds to an effective dose of 1 mSv for occupants [16].

2.2.2. External Hazard Indices

The external hazard index is used to evaluate the external radiological hazard as a result of exposure to gamma rays of natural radioactive sources. The external hazard index (Hex) is assumed to correspond to the maximum acceptable level of the radium equivalent. Thus, Hex must be less than or equal to 1 in order to have an annual effective dose of 1 mSvy−1 [18]. The Hex is expressed as
Hex = (ARa/370) + (ATh/259) + (AK/4810)
where ARa, ATh and AK are the activity concentrations (Bq/kg) of 226Ra, 232Th and 40K, respectively.

2.2.3. Absorbed Dose Rate

The gamma absorbed dose rate evaluates the radiological risk due to terrestrial gamma rays at 1 m above the ground level for the uniform distribution of radionuclides. The absorbed dose rate in nGy/hr is determined by the expression [18,19,20].
D (nGy/h) = 0.462ARa + 0.604ATh + 0.0417AK
where 0.462, 0.604 and 0.0417 are the dose conversion factors of 226Ra, 232Th and 40K, respectively. The UNSCEAR reference level for gamma dose rate is 60 nGyh−1 [20].

2.2.4. Annual Effective Dose

The annual effective dose equivalent (AED) assesses the health hazard related to an individual’s exposure to radiation. The AED measured in mSvy−1 is evaluated based on the dose received from an indoor environment in relation to the indoor occupancy factor and the conversion coefficient from absorbed dose in air to effective dose. The AED is expressed as
AED (mSv/y) = D (nGy/h) × 8760 (h/y) × 0.8 × 0.7 (Sv/Gy) × 10−6
where D is the absorbed gamma dose rate in nGyh−1, 0.7 (Sv/Gy) is the conversion coefficient from absorbed dose in air to effective dose, 0.8 is the indoor occupancy factor and 8760 (h) is the number of hours in a year. The world AED reference level is 0.7 mSv/y [18,19,20].

3. Discussion

Various forms of by-products, either diluted within standard construction materials or used in their original state, were considered for evaluation. These include coal ash, different metallurgical slags, clay and phosphogypsum. Additionally, the evaluation includes Bayer’s process bauxite residue, known as “red mud,” as it finds industrial applications in cement production. Notably, considering its growing annual production in a limited number of large plants and the ongoing research for its usage in various applications such as tile and brick manufacturing, it is highly probable that its utilization will expand in the near future. Similar arguments can be made for most of the residues containing NORMs; however, it is important to acknowledge that process changes may occur, resulting in substantially different residues. For instance, the transition from coal to biomass can lead to significant differences in the composition of ashes.
The average activity concentration of NORM residues and or industrial by-products reusable as building or construction materials from some selected countries and their corresponding radiological hazards are indicated in Table 1. The relative variation in the results and the high radiological hazard indices associated with activity concentration mostly from red mud, gypsum, fly ash and granites are comparatively consistent with literature and other results. The activity concentration of NORM and their corresponding hazard indices in the final building material product from different countries are presented in Table 2. Consequently, there is a reduction in the activities and the indices which are the result of possible mixtures of the NORM residues with other materials.
Mixtures or additives of NORM residues are proven to result in the reduction of activity concentration in the raw residue [21]. As observed from Table 3, the average values of the activity concentration and corresponding radiological hazard indices as applied to the mixture application of the residues in some building materials are relatively low. There is enough literature and publication that points to the possible reduction methods, as shown in Table 3.
These NORM residues are generated in large quantities (Table 4), and would be of high economic benefit while reducing possible radiological effects on humans and the environment if they are relatively incorporated in mixtures or as additive building material production. The global production of bricks, ceramics, plaster made from gypsum and concrete stood at 3.00, 0.11, 0.47 and 7.35 billion tons per year as of 2017 [22,23].
Table
Table 1. Activity concentration and radiological hazard indices of NORM residues in some selected countries.
Table 1. Activity concentration and radiological hazard indices of NORM residues in some selected countries.
CountryType of NORM ResidueActivity Concentration (Bq/kg)Gamma IndexReference
226Ra232Th40K
EUPhosphogypsum38122711.40[24]
Spain237.271.8538.81.33[25]
Turkey 12.52.71141.90.44[26]
Tanzania 6.23.743.70.05[27]
Egypt 92.042.0499.30.68[28]
31.755.0116.00.42[29]
Slovenia & SerbiaPb-Zn Mine By-product34.015.0345.00.30[30]
TanzaniaClay42.931.2107.80.33[27]
HungaryRed Mud265.0264.0283.02.30[31]
180.0264.0283.02.01
China (average)3805073613.92[32,33]
Greece (average)305408333.07[34,35]
Italy97118150.92[36]
Spain100.5321.355.11.96[37]
Coal Ash88.485.1868.01.01[37]
Vietnam77.491.7956.21.04[38]
India118.6147.3352.01.25[19]
North Macedonia69.5634570.70[39]
India77.7125.8373.81.01[40]
EU207805461.27[24]
SpainBlast Furnace Slag96.730.096.10.50[37]
Table
Table 2. Activity concentration and radiological hazard indices of building materials in some selected countries.
Table 2. Activity concentration and radiological hazard indices of building materials in some selected countries.
CountryBuilding MaterialActivity Concentration (Bq/kg)HexGamma IndexDose Rate (nGy/h)Effective Dose Rate (mSv/y)Reference
238U or 226Ra232Th40K
Israel
Israel
Israel		Concrete33.59.263.60.140.1223.690.12[41]
Concrete Mixtures31.99.066.10.130.1722.930.11
Fly Ash Concrete32.79.466.00.140.1223.540.12
Serbia26.422.5243.60.210.2935.940.18[42]
HungaryManganese Clay (Red Mud) Bricks52.040.0607.00.420.5873.500.36[1]
TurkeyBricks15.73.8201.40.030.1434.700.17[26]
Albania33.442.2644.10.390.5467.970.33[43]
SpainPortland Cement15.816.8262.00.160.2328.370.14[37]
Thailand25.716.7140.50.160.2227.810.14[18]
VietnamCement40.127.4253.30.270.3645.640.22[38]
Tanzania46.328.5227.80.290.3791.900.45[27]
Turkey24.720.72493.10.661.02245.171.20[26]
Mean
(Range)		 31.5
(15.7–52.0)		20.5
(3.8–42.2)		439.0
(63.6–2493.1)		0.25
(0.03–0.66)		0.35
(0.12–1.02)		60.10
(22.93–245.17)		0.30
(0.02–1.20)
Table
Table 3. Possible activity concentration and associated radiological hazard reduction methods.
Table 3. Possible activity concentration and associated radiological hazard reduction methods.
Method of ReductionApplicable NORM ResidueReferences
Sulphur polymer metrics with cementPhosphogypsum [44,45]
Binding with zeoliteBottom Ash and Phosphogypsum[46,47]
Firing methodClay for Bricks or Ceramics[1,25]
Proportionate or reducing residue with cement for concrete mixtures NORM Residues, Fly Ash, Bottom Ash, Red Mud, Blast Furnace Slag[17,37,38,42,48,49,50]
Proportionate with Woodchip ashesFly Ash and Bottom Ash[51,52]
Volarisation for cement or Building material productionRed Mud, Bauxite Quarry Waste Limestone, Gypsum, Phosphogypsu, Slag, Ilmenite Mud [30,44]
Alkali activation concreteFly Ash and Red Mud[53,54]
Table
Table 4. Estimated Production of NORM residue usable in building material production (Schroeyers, 2014).
Table 4. Estimated Production of NORM residue usable in building material production (Schroeyers, 2014).
NORM ResidueEstimated Production (Million Tons per Year)
Coal fly ash44
Slag and bottom ash from a coal-fired power plant8
Phosphogypsum from phosphoric acid production180
Red-mud (bauxite residue) from alumina production120
Unprocessed slag from primary iron production260–310
Steel or stainless steel and lead slags130–210
Copper slags24.6
While the reuse of NORM materials in building materials is technically possible, it is important to consider the potential health and safety risks associated with their radioactive nature. The use of NORM materials in construction requires careful handling, monitoring and adherence to regulations and safety guidelines to ensure that radiation exposure to workers and the general public remains within acceptable limits. But as summarized in Table 1, Table 2 and Table 3, the possibility of reusing NORMs residues in some building materials are possible considering the Radioactivity index, though this does not mean the reutilization is guaranteed, and still further research on the metallurgy of building materials is needed, such as hardness, in terms of civil engineering and radiation protection.
At these levels of production without consideration of possible reutilization, the residues and or industrial by-products will increase, leading to possible environmental contamination. If not managed well, the residues may find their way to polluting the air, water and land, especially in the surrounding areas of coal-fired power plants. The radionuclide concentration contents of the residue are also likely to increase or elevate the background radioactivity levels in the environment, which will lead to elevated levels of radon and external gamma dose rates. They also cause the release of alpha and beta particles into the atmosphere [6,31,55,56,57].
In coal-fired power plants, fly ash and bottom ash are the leading solid waste of coal combustion. Fly ash constitutes high amounts of radionuclides and becomes enriched when stockpiled. They are used in the production of ceramic and glass-ceramic, zeolite synthesis, and as filler components for building materials, brick, concrete, cement, asbestos, embankment, road construction, adsorbent and geoplymers [55,56].
Phosphogypsum is a by-product generated by the phosphate industry. The residues can be reutilized for road construction, amendment and reclamation of saline soils and production of building materials such as cement and bricks [6,58].
Gypsum is used mainly in the manufacture of cement, and is also used in concrete production for bridges, buildings and highways. In recent times, gypsum is used for plasterboards for interior designs for modern buildings [59,60]. Gypsum contains more levels of natural radioactivity, particularly radium, than other building materials, and hence will induce high radiation doses, especially since it is being used for interior designs [59].
Red mud is residue from the processing of bauxite, and its chemical composition depends on the type of bauxite ore and the processing parameters. Red mud is mixed with other additives to make building materials such as clay bricks, ceramics and cement [1,60]. Its radiological effects include direct gamma dose rate, radon and thoron exhalation and leaching of natural radionuclides.
Slags from steel, copper, primary iron products and coal-fired power plants can be used in various building materials. For example, steel slag can be used in partial replacement of fine aggregate in both concrete and cement mortar [61]. Slags are also used in bricks and ceramics [62,63,64,65].
Regarding the constructure materials, the gamma index is primarily designed for assessing emitted radiation levels from building materials rather than the constituents of building materials themselves. The gamma index is a measure used to evaluate the gamma radiation emitted from specific building materials and compare it to reference levels or standards.
When considering the radiological sustainability of building materials, it is essential to assess both the radiation levels associated with the materials themselves and the potential impact on human health and the environment. While the gamma index is a useful tool for evaluating radiation levels in building materials, it may not directly address the radiological characteristics of the individual constituents that make up those materials. To address this limitation, it may be necessary to consider additional measures or methodologies that focus on assessing the radiological properties of the specific constituents of building materials. This could involve evaluating the radioactivity concentrations of the individual components or analyzing the potential for radionuclide release during manufacturing, usage or disposal processes.
By expanding the assessment beyond the gamma index and incorporating considerations specific to the constituents of building materials, a more comprehensive understanding of the radiological sustainability of these materials can be achieved. This broader approach would ensure that the potential radiological impacts associated with both the building materials as a whole and their individual constituents are taken into account.
In the context of radiological studies, measures such as the gamma index and hazard indices are typically used to assess radiation levels and potential risks. These measures help evaluate the radiological impact of activities or materials and guide decisions regarding safety and sustainability.
However, radiological sustainability is not solely determined by these measures. Other factors are also important considerations. These factors include potential environmental contamination, effects on building materials, cost implications, waste production rates, hazardous/toxic components and geographical considerations.
The decision to reuse NORMs (Naturally Occurring Radioactive Materials) or manage them as waste involves a comprehensive evaluation that goes beyond radiological considerations alone. While radiological factors play a significant role, other factors such as cost-effectiveness, waste management strategies, logistical feasibility and potential environmental impacts need to be taken into account.
In summary, radiological sustainability involves considering a range of factors beyond just radiological measures. Decisions regarding the reuse or disposal of NORM materials require a comprehensive evaluation that encompasses radiological considerations, cost factors, waste management strategies, potential environmental impacts and logistical feasibility, among others. Each situation may have unique circumstances that need to be carefully evaluated to ensure a sustainable and responsible approach to radiological practices.
Therefore, developing a broader “NORM Potential Reutilization” index could be a valuable approach to assessing the sustainability of NORM materials. Such an index would consider not only the radiological parameters, but also other factors like economic viability, environmental impacts and social acceptability. Not necessarily, but integrating radiological parameters into existing sustainability indexes, such as Environmental Cost Indicators (ECIs), can also enhance the comprehensiveness and effectiveness of these tools. By incorporating radiological considerations into broader sustainability frameworks, it becomes possible to evaluate the potential re-use of NORM materials in a more holistic manner. This approach would provide decision-makers with a comprehensive view of the benefits and drawbacks associated with NORM re-use, considering both radiological risks and other sustainability factors.
While this concept is new and not yet fully investigated, more studies and attention to this matter is required, as the development of a NORM re-use index or the integration of radiological parameters into existing indexes would require collaboration among experts from various fields, including radiological sciences, environmental sciences, economics and policy-making.
Therefore, this unique interdisciplinary approach would ensure a well-rounded evaluation of NORM re-use practices and facilitate informed decision-making. Additionally, initiating discussions and research on integrating radiological parameters into sustainability indexes can contribute to the advancement of sustainable practices in industries dealing with NORM materials. This would foster awareness about the importance of considering radiological aspects alongside other sustainability indicators, and encourage the development of standardized guidelines and frameworks for evaluating NORM re-use.
Overall, more comprehensive studies (including treatment techniques, partial mix possibility, etc.) are needed for expanding the assessment framework beyond radiological parameters and exploring the integration of radiological considerations into broader sustainability indexes, which would help promote a more comprehensive and balanced approach to NORM re-use, taking into account environmental, economic, social and radiological aspects.

4. Conclusions

The concept of radiological sustainability is new in environmental science, and it is early in the investigative journey to an environmentally sustainable future. No such studies or definition in this regard have been recorded, and it might be for the first time that this matter would be considered to have an extra environmental sustainability. Therefore, as the scientific data in this space are limited, and there are many gaps in knowledge regarding radiological sustainability in this report, a comprehensive review study was conducted to find out if building material sustainability from the viewpoint of environmental radioactivity would be achieved or not. The radiological sustainability, recycling or reutilization of residue or by-products which contain NORMs, rather than disposing of as waste, is the first consideration to achieve sustainability. This study reviews the concept of radiological sustainability of the reutilization of NORM residue in building materials. The importance of using NORM residues has increased in recent decades, due to the reduction of environmental pollutants and the achievement of sustainability in the human environment. However, NORM residues are generated in large quantities, and without the consideration of possible reutilization, the management of these wastes would preserve severe challenges and would eventually lead to environmental contamination. This is to say that the reutilization of NORM residues provides better financial and environmental solutions while reducing possible radiological effects on humans. NORM residue or waste could become a high material resource for the cement industry. In this regard, the assessment of radium equivalents (Raeq) and external and internal indexes (I-indexes) are useful tools to classify NORM residues before their inclusion in building products. This assessment and or indexes reflect the risk of external exposure much better than the specific activity concentration of Ra-226, Th-232 and K-40. Equally, building material properties such as density and thickness should be taken into consideration when designing building materials that contain NORM residue. Furthermore, mixtures or additives of NORM residues are proven to result in the reduction of activity concentration in the raw residue with other raw materials, and this offers flexible reuse options depending on the final product.
However, there are some limitations regarding the legislation and public health, but remediation of some residue products and building materials, as well as mixture, could make them possible to be reused or reutilized as building materials. More investigation regarding this matter is required.

Author Contributions

Conceptualization, A.S. and L.T.-L.; methodology, A.S., L.T.-L. and E.O.A.-k.; sof; validation, A.S., T.K. and E.T.-B.; analysis and investigation, A.S., L.T.-L., T.K. and E.O.A.-k.; and writing—original draft preparation, L.T.-L., A.S. and E.O.A.-k. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

All data is presented at the paper.

Conflicts of Interest

The authors declare no conflict of interest.

References

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Sustainability 15 10647 g001 550
Figure 1. Data acquisition and selection process.
Figure 1. Data acquisition and selection process.
Sustainability 15 10647 g001
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Shahrokhi, A.; Tettey-Larbi, L.; Akuo-ko, E.O.; Tóth-Bodrogi, E.; Kovács, T. The New Conception of Radiological Sustainability Possibilities by Reutilization of Residues Products and Building Materials. Sustainability 2023, 15, 10647. https://doi.org/10.3390/su151310647

AMA Style

Shahrokhi A, Tettey-Larbi L, Akuo-ko EO, Tóth-Bodrogi E, Kovács T. The New Conception of Radiological Sustainability Possibilities by Reutilization of Residues Products and Building Materials. Sustainability. 2023; 15(13):10647. https://doi.org/10.3390/su151310647

Chicago/Turabian Style

Shahrokhi, Amin, Lordford Tettey-Larbi, Esther Osei Akuo-ko, Edit Tóth-Bodrogi, and Tibor Kovács. 2023. "The New Conception of Radiological Sustainability Possibilities by Reutilization of Residues Products and Building Materials" Sustainability 15, no. 13: 10647. https://doi.org/10.3390/su151310647

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