Assessment of bentonite, zeolite, and sodium alginate for soil stabilization in dust hotspots

Abstract

Dust emissions from degraded soils in arid and semi-arid regions pose significant environmental and health risks, requiring sustainable mitigation strategies. This study evaluates bentonite, zeolite, and sodium alginate as soil stabilizers to reduce dust emissions and enhance crust formation in three major dust hotspots (DS1, DS2, and DS3) around Lake Urmia, Iran. Soil samples were treated with bentonite and zeolite at 2%, 4%, and 6% w/w, with and without 0.5% w/w sodium alginate. Crust thickness, mean compressive strength, and maximum compressive strength were measured, followed by FTIR and FESEM analyses to assess structural changes. Results showed that 6% bentonite substantially improved soil stability, increasing crust thickness and compressive strength to 15.22 mm and 5260.42 kPa in DS2, respectively. Zeolite at the same concentration provided moderate improvements, producing a crust thickness of 10.11 mm and compressive strength of 3333.94 kPa, particularly in finer-textured soils. Adding sodium alginate enhanced crust formation at lower bentonite levels but exhibited inconsistent effects on compressive strength. FTIR analysis confirmed strengthened Si-(Al)-O and Si–O-Al stretching bands, and FESEM imaging revealed denser, more cohesive crust structures following treatment. This study provides a novel, comparative assessment of mineral and biopolymer stabilizers across multiple dust hotspots with contrasting soil textures. The findings offer practical guidance for selecting cost-effective and environmentally sustainable soil stabilization strategies tailored to site-specific conditions. Overall, the results highlight bentonite as the most effective stabilizer, with zeolite and sodium alginate offering complementary, site-specific benefits for sustainable dust-mitigation approaches.

Supplementary Information

The online version contains supplementary material available at 10.1038/s41598-026-56356-1.

Introduction

Desertification is a major global environmental challenge, affecting nearly 30% of Earth’s surface and producing significant economic, social, and ecological consequences^1,2. Driven by climate change and unsustainable human activities, it accelerates land degradation, reduces fertile areas, and worsens food insecurity³. Dust storms associated with desertification further contribute to air pollution and pose serious health risks, especially in arid and semi-arid regions where respiratory diseases are increasingly prevalent⁴. These wide-ranging impacts highlight the urgent need for proactive strategies to control emerging dust hotspots^5,6.

Lake Urmia, a major saline lake in northwestern Iran, serves as a critical case study for desertification-related degradation. Once among the world’s largest saline lakes, it has experienced a dramatic 90% decline in water volume due to climate change, reduced precipitation, intensified evaporation, and unsustainable water management^7–9. The retreat of the lake has exposed vast playa surfaces highly prone to dust emission^10,11. These newly exposed sediments—characterized by sparse vegetation, low organic matter, sandy texture, and abundant calcium carbonate minerals such as aragonite and calcite—are extremely vulnerable to wind erosion¹².

The degradation of Lake Urmia reflects environmental crises observed in other desiccated lakes, including the Aral Sea, Owens Lake, and the Great Salt Lake¹³. These systems illustrate the high potential for dust emission from dried lakebeds, where saline and fine particles become airborne and create serious risks for agriculture and human health^14,15. Dust from these regions has been linked to soil salinization, orchard damage, and increased respiratory illnesses, highlighting the far-reaching socio-environmental impacts of such phenomena.

Efforts to stabilize dust-prone surfaces have utilized a variety of strategies, encompassing mechanical, chemical, and biological approaches, each with distinct advantages and limitations^16–18. Mechanical methods such as barriers or sand fences are widely used but often remain temporary, damage-prone, and costly to maintain^19,20. Chemical stabilizers like sodium chloride, magnesium chloride, or bitumen can reduce dust emissions^21–25 yet their expense and environmental risks—especially with petroleum-based materials—limit their applicability^26,27. Biological approaches offer longer-term potential but require substantial water, high costs, and long establishment periods in arid regions^28-31.

In recent years, there has also been a growing global interest in utilizing natural minerals and quarry by-products as sustainable alternatives for enhancing weak and dredged soils. Studies from Asia have shown that boulder crusher dust can effectively enhance sediment strength and compaction^32,33 while European research highlights both the potential and the regulatory challenges associated with reusing dredged materials³⁴. These findings point to a broader international movement toward sustainable, mineral-based soil stabilization practices. Similarly, recent geotechnical studies on sodium-rich and dispersive soils have shown that mineral-based and waste-derived additives containing calcium or potassium can significantly improve soil stability through ion exchange, flocculation, and microstructural densification^35-37.

Across many recent studies, bentonite, zeolite, and sodium alginate have been recognized as promising, environmentally friendly materials for stabilizing soils exposed to wind erosion. Bentonite is noteworthy for its water retention, adhesiveness, and swelling capacity—properties that improve soil cohesion and reduce erosion^38,40,41. Bentonite’s strong swelling behavior and high cation-exchange capacity allow it to form cohesive matrices that reduce particle detachment, while zeolite contributes through its porous structure, moisture retention capacity, and chemical buffering effects^41–43. Their performance can be strengthened when used with polymer mulches⁴⁴. Sodium alginate, meanwhile, forms durable surface crusts that bind soil particles and enhance the longevity of mineral amendments^12,45,46. Together, these materials offer a robust, sustainable, and multifunctional approach to improving soil stability in dust-prone environments.

However, despite the growing body of research on mineral and biopolymer-based soil stabilizers, most existing studies have focused on individual materials or binary combinations, primarily evaluating bentonite or polymer additives separately. In particular, the role of zeolite in dust mitigation remains comparatively underexplored, especially in saline playa environments. Moreover, the combined application of bentonite, zeolite, and sodium alginate as an integrated stabilization system—and its effects on both dust suppression and mechanical strength—has not yet been systematically investigated. This gap limits the development of optimized, multifunctional, and sustainable dust-control strategies for highly erodible lakebed sediments.

To address these gaps, this study investigates the combined use of bentonite, zeolite, and sodium alginate as a sustainable soil-stabilization strategy for mitigating dust emissions from the exposed margins of Lake Urmia. Specifically, the objectives of this study were to:

1. Evaluate the effectiveness of bentonite and zeolite in reducing dust emissions,

2. Assess sodium alginate’s role in enhancing compressive strength and stabilization, and

3. Determine optimal bentonite and zeolite concentrations across three dust hotspot areas.

By achieving these objectives, the research aims to advance sustainable dust control strategies, mitigate environmental and health impacts, and offer practical solutions for improving soil stability in arid and semi-arid regions worldwide.

Materials and methods

Study area, soil sampling and analysis

The study focused on three major dust emission sources identified in previous research around the periphery of Lake Urmia, in northwestern Iran^10,11,47 (Fig. 1a and 1c). Dust Source 1 (DS1) consist of sandy deposits approximately 35 km north of Lake Urmia on its western margin. Dust Source 2 (DS2) comprises sandy-saline surfaces in the southeastern part of the lake, near the village of Akhond Qeshlaq. Dust Source 3 (DS3) includes sandy deposits near Ajabshir on the lake’s eastern side (Fig. 1b).

Fig. 1.

Geographic overview of the study area. (a) Global map highlighting the location of Iran. The red circle indicates the study region. (b) Detailed map of the Lake Urmia basin. The satellite imagery of Lake Urmia (acquired on January 1, 2021) and the global map base layer were retrieved from Google Earth (https://earth.google.com/); image data: Landsat/Copernicus. The images were georeferenced using ArcGIS (v. 10.8). Black circles indicate the specific sampling sites (DS1, DS2, and DS3) along the lake margins. Field photographs of the sampling sites (DS1, DS2, and DS3) were captured by the authors.

Surface soil samples were collected from the top 0–5 cm layer, which represents the wind-erodible surface zone of playa sediments where loose fine particles responsible for dust emissions are concentrated. Samples were taken from 10 locations within each region and combined to create composite samples representative of the respective areas. These composite samples were then transported to the Soil Science Laboratory at the University of Maragheh for detailed analysis and characterization. Table 1 presents the physicochemical properties of soil samples from the investigated dust sources.

Table 1.

Physicochemical characteristics of soil samples from the three investigated dust sources.

Parameter	DS1	DS2	DS3	method	reference
pH	8.60	7.80	8.24	1:2.5 soil to water	Sparks et al.48,
EC (dS/m)	30.00	40.00	8.65	1:2.5 soil to water
CCE (%)	47.00	17.25	18.63	titration	Sparks et al.48,
OC (%)	0.39	0.36	0.00	wet combustion	Nelson and Sommers49
EF (%)	90.20	84.50	95.00	Particles < 0.84 mm by dry sieving	Nimmo and perkins50
Clay (%)	14.00	24.00	4.00	hydrometer
Silt (%)	7.00	14.00	14.00		Gee and Or51
Sand (%)	79.00	62.00	82.00

Values represent the mean of multiple samples collected from each site.

EC: electrical conductivity; CCE: calcium carbonate equivalent; OC: organic carbon; EF: erodible fraction.

The particle-size distribution curves of the soil samples collected from the dust source areas are presented in Fig. 2. Particle-size distribution was determined using an LS 13,320 laser diffraction analyzer, and the results are displayed as histograms to illustrate the relative frequency of particle diameters and facilitate comparison among the sampling sites. As shown in Fig. 2, the majority of particles fall within the fine sand and silt fractions, with only a limited proportion of clay-sized particles. This pattern reflects the high erodibility of the exposed playa sediments and supports their characterization as dust-prone materials.

Fig. 2.

Particle size distribution curves for the three selected sampling sites on the margins of Lake Urmia.

Experimental setup

FTIR characterization and application of bentonite and zeolite in dust stabilization

The structural properties and FTIR peaks of bentonite and zeolite make them effective dust stabilizers. Bentonite’s strong water retention is highlighted by the -OH and H–O-H stretching vibrations (~ 3400 cm⁻¹ and ~ 3620–3700 cm⁻¹), which enhance its swelling capacity and bind dust particles, reducing their mobility. Its layered structure, reflected in the Si–O (~ 1000–1100 cm⁻¹) and Al–O–Si (~ 500–600 cm⁻¹) bending peaks, enhances surface reactivity, increasing adhesiveness and aggregation. This encapsulates dust particles, minimizing their dispersion.

Zeolite’s porous crystalline framework, indicated by Si–O stretching (~ 1000–1100 cm⁻¹) and T-O-T bending (~ 400–500 cm⁻¹) vibrations, facilitates moisture adsorption and dust entrapment. The presence of hydrophilic surfaces is confirmed by H–O-H bending (~ 1640 cm⁻¹) and -OH stretching bands (~ 3400–3600 cm⁻¹), which enhance particle cohesion and reduce dispersion. In addition, its aluminosilicate structure supports ion exchange and electrostatic interactions, further strenthing interparticle bonding. Zeolite is particularly effective with coarse particles, filling voids, absorbing moisture, and forming a robust bonded network, reducing dust re-suspension in windy conditions.

Figure 3 presents FTIR spectra of bentonite and zeolite, and Table 2 summarizes key FTIR peaks from suppliers in northwestern Iran. The FTIR spectra confirm bentonite’s primary montmorillonite content, with characteristic peaks at ~ 530 cm⁻¹ (Al–O–Si bending), ~ 1035 cm⁻¹ (Si–O stretching), ~ 1640 cm⁻¹ (H–O-H bending), and ~ 3620 cm⁻¹ (O–H stretching). Zeolite’s peaks at ~ 460 cm⁻¹ (O-Si–O bending), ~ 790 cm⁻¹ (Si–O symmetric stretching), ~ 1000–1100 cm⁻¹ (Si–O and Al-O asymmetric stretching), and ~ 3440 cm⁻¹ (O–H stretching) confirm its identification. The alignment of these peaks with known values underscores the materials’ suitability for dust stabilization.

Fig. 3.

FTIR spectra of bentonite and zeolite highlighting key characteristic peaks.

Table 2.

Key FTIR peaks for bentonite and zeolite characterization and identification.

	Wavenumber (cm⁻1)	Peak assignment	Material property
Bentonite	3620–3700	-OH stretching (inner hydroxyl groups)	Presence of structural hydroxyl groups in clay
	3400–3450	H–O-H stretching (water)	Adsorbed water on bentonite surface
	1640–1650	H–O-H bending (water)	Indicates interlayer water in the structure
	1000–1100	Si–O stretching (silicate framework)	Tetrahedral silicate structure
	500–600	Al–O–Si bending	Alumino-silicate framework characteristic
Zeolite	Wavenumber (cm⁻1)	Peak assignment	Material property
	3400–3600	-OH stretching (surface hydroxyl groups)	Hydrophilic surface of zeolite
	1640–1650	H–O-H bending (water)	Adsorbed moisture within zeolite pores
	1000–1100	Si–O stretching (aluminosilicate framework)	Crystalline porous aluminosilicate framework
	450–500	T-O bending (T = Si or Al)	Tetrahedral framework vibrations

Preparation of bentonite and zeolite treatments

To ensure a systematic evaluation of the effects of clay amendments on soil physical properties, bentonite and zeolite were prepared at four concentration levels (0, 2, 4, and 6% w/w, based on soil dry weight). These dosage levels were selected based on their documented influence on soil structure and hydraulic conductivity and to allow detection of dose-dependent responses. Each amendment was thoroughly blended with the upper 3–5 cm of air-dried soil in three replicates. Mixing was performed manually for 10 min followed by mechanical stirring to ensure complete homogeneity and prevent layering of clay particles. Soil moisture was then gradually adjusted to field capacity using a fine-mist sprayer to guarantee uniform wetting across all treatments.

It is worth mentioning that field capacity (FC) was not measured experimentally in this study; rather, FC was estimated from the soil’s saturation percentage (SP) using an empirical relationship commonly applied in soil physics, where FC is approximated as one-third of the saturation percentage (FC ≈ 0.33 × SP). This approach provides a reasonable estimation for light-textured, sandy soils such as those evaluated in this study, where direct FC measurement was not performed.

A key innovation of the present study lies in the second experimental phase, where 0.5% sodium alginate (w/w) was incorporated directly into the soil–clay mixture along with either bentonite or zeolite. In contrast to earlier studies using aqueous alginate solutions, the present approach involved dry blending the sodium alginate powder uniformly with the soil and the respective clay amendment prior to moisture adjustment. This method was selected to allow consistent distribution of the polymer throughout the soil matrix and to examine its potential synergistic interaction with the clay minerals under realistic soil-application conditions. The choice of the 0.5% alginate level was based on findings by Hamzehpour et al.⁵² and Alkhayer et al.²¹, which showed that low concentrations enhance crust stability more effectively than higher doses.

Measurement of soil crust properties

The thickness of the soil crusts was measured using a digital caliper with a precision of 0.1 mm. Surface strength was assessed using an automatic penetrometer (Model MP11, Iran). Measurements included the maximum and average penetration pressures, recorded at a penetration speed of 0.3 mm s⁻¹ to a depth of 30 mm. The maximum applied pressure was set at 12,000 kPa, to ensure accurate evaluation of the crust’s mechanical properties.

Water retention capacity

The water-holding capacity of soils treated with bentonite and zeolite as well as untreated control samples was assessed over a 20-day period for three dust sources (DS1, DS2, and DS3). Soil samples were saturated with water, and their weights were recorded at 4-days intervals to monitor water retention. The remaining water content was calculated as the amount of water still retained in the sample at each measurement time, obtained from the difference between the current weight and the oven-dry weight. The study focused on the remaining water content on day 12, a time point where significant differences across treatments were observed. Additionally, the slope of the decline in water content, derived from the plotted water retention curves, was analyzed to quantify the rate of water loss.

It is important to note that the water-retention experiment was conducted as an independent complementary assessment and was not used to interpret the compressive-strength or crust-thickness results. All mechanical tests were performed on fully dried soil samples; therefore, water content at earlier stages does not influence the strength measurements. The purpose of the water-retention test was to evaluate the moisture-related component of wind-erosion resistance, as soils with higher moisture levels require stronger winds for particle detachment even before a crust fully develops.

Microscopic and spectroscopic analysis

The structural changes in soil aggregates were analyzed using field emission scanning electron microscopy (FESEM) (FE-SEM ZEISS Sigma 300). FESEM imaging can provide detailed insights into aggregate formation facilitated by bentonite and zeolite treatments. Fourier-transform infrared spectroscopy (FTIR) was conducted to detect the formation of new chemical bonds associated with clay minerals, such as silicon-oxygen-aluminum linkages, thereby evaluating the effectiveness of the treatments. The functional groups in the developed crust samples were identified using attenuated total reflectance (ATR) FTIR spectroscopy. FTIR spectra were recorded with a Spectrum Two (Perkin Elmer, USA) spectrometer, covering the range of 400–4000 cm⁻¹.

Statistical design and data analysis

This research consisted of four separate experiments, each designed to evaluate the effect of one type of soil amendment on the physical properties of three soils collected from dust hotspots. All experiments were conducted as a factorial arrangement of 3 × 4 in a completely randomized design (CRD) with three replications. The first factor was soil type at three levels (DS1, DS2, and DS3), and the second factor was the amendment application rate at four levels (0, 2, 4, and 6% w/w). Accordingly, each experiment included 12 treatments (3 × 4) and a total of 36 experimental units.

• Experiment 1: Application of bentonite at four levels (Bent-0, Bent-2, Bent-4, and Bent-6 w/w).

• Experiment 2: Application of zeolite at four levels (Zeo-0, Zeo-2, Zeo-4, and Zeo-6 w/w).

• Experiment 3: Application of bentonite combined with 0.5% sodium alginate at four levels (Bent-SA-0, Bent-SA-2, Bent-SA-4, and Bent-SA-6 w/w).

• Experiment 4: Application of zeolite combined with 0.5% sodium alginate at four levels (Zeo-SA-0, Zeo-SA-2, Zeo-SA-4, and Zeo-SA-6 w/w).

For each of the four experiments, the following analysis of variance (ANOVA) model was applied:

where:

• : observed value of the dependent variable (crust thickness, maximum compressive strength, mean compressive strength, etc.) for soil type i, amendment level j, and replication k

• μ: overall mean

• : fixed effect of soil type

• : fixed effect of amendment level

• : interaction effect between soil type and amendment level

• : random error term assumed to follow a normal distribution

Prior to conducting ANOVA, the normality of residuals (Shapiro–Wilk test) and homogeneity of variances (Bartlett’s or Levene’s test) were examined. When main effects or interactions were significant, treatment means were compared using Duncan’s Multiple Range Test (DMRT) at the 5% significance level. All statistical analyses were performed using SAS 9.4 software.

Results and discussion

The role of treatments in enhancing the physical properties of induced soil crusts

Figure 4 summarizes the effects of all amendment types on three key crust properties—crust thickness, maximum compressive strength, and mean compressive strength—across the three dust source soils collected around Lake Urmia. Each row represents one amendment category (bentonite (Bent), zeolite (Zeo), bentonite with 0.5% sodium alginate (Bent-SA) and zeolite with 0.5% sodium alginate (Zeo-SA)), while each column corresponds to one mechanical parameter. Within each subplot, the amendment rates (0%, 2%, 4%, and 6%) are shown for Dust Sources (DS1, DS2, and DS3). Different lowercase letters above the bars indicate statistically significant differences among treatments (p < 0.05). This structure allows direct comparison of how each amendment and concentration level influences crust development in each soil type. The full statistical analyses, including ANOVA results and mean comparison tables, are provided in Tables S1, S2, S3, S4, S5, S6, S7, S8 in the Supplementary File.

Fig. 4.

Crust thickness (left column), maximum compressive strength (middle column), and mean compressive strength (right column) of soil crusts formed from dust sourced from three regions around Lake Urmia under different amendment treatments and application rates (0%, 2%, 4%, and 6%). Treatments include: bentonite (a, b, c), zeolite (d, e, f), bentonite combined with 0.5% sodium alginate (g, h, i), and zeolite combined with 0.5% sodium alginate (j, k, l). Different lowercase letters above the bars indicate statistically significant differences among treatments (p < 0.05). The figure highlights how amendment type and concentration influence crust thickness, structural resistance, and overall mechanical stability across the three dust source areas.

Effect of bentonite treatments

Figure 4a–c and Fig. 5 illustrate the development of soil crusts formed with bentonite across the three dust-prone soils. In the control treatments, crusts were weak and often disintegrated during handling, confirming the inherently low cohesion of the untreated soils. The addition of bentonite markedly improved crust formation in all soils, producing thicker and more mechanically stable crusts.

Fig. 5.

Images of crusts developed by mixing bentonite at different concentrations (0%, 2%, 4%, and 6%) with three soils from dust source areas (DS1, DS2, and DS3).

As shown in Fig. 4a, DS2 produced the thickest crusts, reaching 18.91 mm at the Bent-4, an increase of 15.22 mm compared to the Bent-0. Although Bent-6 produced similar thickness, the difference from Bent-4 was not statistically significant. In DS1 and DS3, the thickest crusts formed at Bent-6, increasing crust thickness by 11.63 mm and 11.33 mm over their respective controls. Overall, bentonite enhanced crust thickness by more than 1 cm in all soils, demonstrating a strong stabilizing effect.

Crust strength followed the same general pattern. DS2 recorded the highest maximum and mean compressive strengths at 5632.03 kPa and 1619.28 kPa under Bent-6, representing improvements of 5260.42 kPa and 1537.36 kPa over the Bent-0. DS1 and DS3 also reached their highest strengths at Bent-6, with DS3 achieving values statistically comparable to DS2 (Fig. 4b and c). These results confirm that bentonite effectively increases both crust thickness and mechanical resistance, with the strongest responses occurring in DS2 and DS3.

Effect of zeolite treatments

Figure S1 (Supplementary File) illustrates the soil crusts formed under zeolite treatments across the three dust source soils. Similar to the bentonite results, zeolite improved crust stability relative to the untreated controls; however, the magnitude of improvement was generally lower. DS2 showed the strongest response to zeolite, producing well-formed and durable crusts at 4% (Zeo-4) and 6% (Zeo-6) application rates, whereas DS1 and DS3 exhibited more modest improvements.

Figure 4d–f indicates that DS2 achieved the greatest crust thickness under zeolite, reaching an average of 13.80 mm, an increase of 10.11 mm over its control. Although this reflects a clear enhancement, the maximum crust thickness produced by zeolite remained noticeably lower than that produced by bentonite in the same soil (18.91 mm). Interestingly, the optimal rate for DS2 under Zeo-2, mirroring the bentonite trend, suggesting that DS2 is highly responsive to low amendment levels regardless of material type.

In DS1 and DS3, the thickest crusts occurred at Zeo-4 and Zeo-6, again showing improvements relative to the control but producing thinner crusts than the corresponding bentonite treatments. Compressive strength results followed a similar pattern. DS2 achieved the highest mechanical resistance in Zeo-6, with mean and maximum compressive strengths of 1666.09 kPa and 3705.55 kPa, respectively—improvements of 1584.17 kPa and 3333.94 kPa over Zeo-0 treatments. Nevertheless, these values remained substantially lower than those achieved with the Bent-6, highlighting bentonite’s superior binding and thickening capability.

Overall, zeolite contributed to significant crust reinforcement across the three soils, but its effects were consistently weaker than those of bentonite. The contrast between the two materials underscores their differing physicochemical interactions with the fine dust-rich soils of the Lake Urmia region.

Effect of bentonite-sodium alginate treatments

Figure S2 (Supplementary File) shows the crusts produced with combined bentonite–sodium alginate treatments. The incorporation of 0.5% sodium alginate generally improved crust formation relative to the untreated controls; however, crust thicknesses were typically lower than those obtained from bentonite-only treatments. Among the three soils, DS3 showed the strongest positive response to the combined amendment, forming stable crusts even at lower bentonite application rates (Fig. 4g–i).

In DS1, crust thickness did not differ significantly between the Bent-SA-2 and Bent-SA-6, whereas DS3 achieved its maximum thickness at Bent-SA-6, increasing by 7.36 mm and 11.30 mm relative to the controls in DS1 and DS3, respectively. Mechanical properties reflected similar trends. DS3 attained the highest mean and maximum compressive strengths in Bent-SA-6 (1596.84 kPa and 3500.92 kPa), values comparable to those achieved under bentonite-only conditions. In contrast, DS1 and DS2 experienced notable reductions in strength when sodium alginate was added. In DS1, maximum strength decreased sharply from 2577 kPa (bentonite-only) to 653.15 kPa, and in DS2 from 618.33 kPa to 304.89 kPa.

These reductions can be attributed to the physicochemical effects of sodium alginate on crust microstructure. The polymer increases the viscosity of the pore solution and promotes the formation of larger, loosely bound aggregates, resulting in wider pore spaces and a less compact fabric. Moreover, its high solubility and moisture sensitivity can lead to uneven redistribution during drying, increasing spatial variability in binding efficiency. Such conditions weaken crust rigidity, particularly in soils with lower clay content (DS1 and DS2), where fewer mineral surfaces are available for effective cross-linking. Consequently, DS1 experienced the greatest loss in strength, with a reduction of 1923.85 kPa.

Effect of zeolite-sodium alginate treatments

Figure S3 (Supplementary File) illustrates the soil crusts formed using combined zeolite–sodium alginate treatments. While the addition of sodium alginate improved surface cohesion and produced more uniform crusts, the resulting crusts were generally thinner and mechanically weaker than those obtained with zeolite alone. This pattern was most evident in DS2, where crust thickness decreased to an average of 8.91 mm under the combined treatment compared with 13.8 mm in the zeolite-only condition (Fig. 4j–l).

The reduction in thickness in DS2 under Zeo-SA treatments can be attributed to the interaction between sodium alginate and the inherently porous structure of zeolite. Sodium alginate forms a viscous gel coating around zeolite particles, limiting their ability to interlock and reducing particle packing density. Consequently, the crust develops a more open and less compact microstructure with wider pore spaces, which restricts overall compaction and final crust formation. In contrast, DS1 and DS3 showed modest improvements in crust thickness at the higher application levels (particularly Zeo-SA-6 treatment), likely due to their coarser textures and lower clay mineral activity. In such soils, sodium alginate can bridge larger particles more effectively, providing a temporary structure-enhancing effect.

Compressive strength results mirrored the thickness trends. The highest strength values for the Zeo-SA treatments were observed in DS2, reaching 895.43 kPa (mean) and 1537.88 kPa (maximum). However, these values remained consistently lower than those achieved under zeolite-only treatments. This decline reflects reduced particle interlocking and weaker matrix bonding caused by alginate coating the zeolite surfaces, which decreases frictional resistance and limits the formation of a dense, load-bearing crust.

Effect of treatments on compressive strength across crust depths in dust sources

Figure 6 presents compressive strength profiles across crust depths for various treatments and concentrations in the three DSs. In DS1, Bent-6 achieved the highest compressive strength, peaking at ~ 3500 kPa near the surface (~ 5 mm) and tapering off beyond ~ 10 mm, indicating a strong but shallow crust (Fig. 6a). Bent-SA exhibited a lower peak (~ 2500 kPa), suggesting that the addition of sodium alginate slightly reduced strength due to dilution effects (Fig. 6d). The Zeo-6 treatment reached ~ 3000 kPa but weakened rapidly with depth, forming a less cohesive crust (Fig. 6g). Zeo-SA performed the weakest, with peak strength below 1000 kPa, indicating minimal reinforcement (Fig. 6j). Overall, Bent-6 was the most effective treatment for DS1, creating the strongest surface crust, while sodium-alginate mixtures and zeolite-based treatments were comparatively less effective.

Fig. 6.

Compressive strength profiles across crust depth (mm) for all treatments in the three dust sources. Panels (a–c) present the bentonite treatments for DS1, DS2, and DS3, respectively; panels (d–f) illustrate bentonite combined with sodium alginate; panels (g–i) show the zeolite treatments; and panels (j–l) display zeolite combined with sodium alginate. Each color represents a different amendment concentration (0%, 2%, 4%, and 6%), highlighting variations in compressive strength across crust depth for each dust source and treatment.

For DS2, Bent-6 performed best, peaking at ~ 6000 kPa near 5 mm depth and maintaining strength up to 10 mm, forming a thick and cohesive crust (Fig. 6b). Bent-SA-4 showed a lower peak (~ 2000 kPa) but extended the crust depth, indicating reduced peak strength but improved uniformity (Fig. 6e). Zeolite peaked at ~ 3500 kPa with a gradual decline in strength (Fig. 6h), while Zeo-SA performed poorly, with peak strength below 1800 kPa (Fig. 6k).

For DS3, Bent-6 again achieved the highest strength (~ 3500 kPa), declining beyond 10 mm and forming a cohesive crust (Fig. 6c). Bent-SA exhibited a similar peak (~ 3500 kPa) but maintained higher strength values down to ~ 20 mm depth, indicating enhanced crust uniformity at greater depths (Fig. 6f). Zeolite peaked at ~ 2500 kPa and produced stronger and deeper crusts than bentonite (Fig. 6i), while Zeo-SA remained the weakest, with strength below 1600 kPa and high variability (Fig. 6l).

Across all soils, Bent-6 consistently produced the strongest and most cohesive crusts, with DS2 showing the highest peak strength (≈6000 kPa). Treatments containing sodium alginate exhibited lower peak surface strength but improved strength retention with depth, particularly in DS3. This behavior reflects the different mechanisms involved: while bentonite and zeolite alone tend to form dense but brittle surface crusts with strength declining sharply below the top few millimeters, the addition of sodium alginate produces a more ductile matrix. The biopolymer forms a gel-like network that extends deeper into the soil pores, creating continuous bonding between particles and resulting in a measurable residual strength across crust depths.

Zeolite treatments provided moderate crust formation but remained less effective than bentonite, and the Zeo-SA mixtures were the weakest overall, largely due to alginate coating zeolite grains and limiting particle interlocking. Overall, Bent-6 remains the most effective treatment, producing strong, cohesive crusts across all dust sources. Bentonite combined with sodium alginate can be considered a secondary option for DS3, where the improved depth-related strength may offer an advantage. These results confirm bentonite’s superior performance compared to both zeolite and sodium alginate–based treatments, establishing it as the primary stabilizer for mitigating dust emission.

Water-holding capacity of bentonite and zeolite treatments

The water-holding capacity of soils treated with bentonite and zeolite at various concentrations was evaluated over a 20-day period for DS1, DS2, and DS3 (Fig. 7). To further analyze treatment efficacy, the remaining water content on day 12, along with the slope of decline in water content (calculated from Fig. 7), is presented in Fig. 8. Day 12 was selected because all treatments showed a clear inflection point in the drying curves at this stage, where the initial rapid drainage phase transitioned to a slower capillary-controlled drying phase. This breakpoint marks the point at which differences among treatments were at their maximum before the curves began to converge. By day 20, all soils had nearly dried completely, regardless of treatment. However, significant differences in the slope of decline and remaining water content at day 12 were observed across treatments and DSs, making day 12 a critical point for comparative analysis.

Fig. 7.

Water-holding capacity of DS1, DS2, and DS3 over 20 days under various treatments. Panels (a), (b), and (c) represent DS1, DS2, and DS3, respectively. Each curve corresponds to a specific treatment, including Bentonite (2%, 4%, 6%), Zeolite (2%, 4%, 6%), and the untreated sample (0%).

Fig. 8.

Comparison of water retention and loss as a function of the slope of decline. Green bars represent the percentage of remaining water on Day 12 for each treatment, while blue bars indicate the slope of decline in water content over the experiment. Higher green bars and gentler (less negative) blue slopes reflect better water retention. (a) DS1; (b) DS2; (c) DS3.

For DS1, the control exhibited poor water retention, declining to ~ 249 g by day 20. Bentonite treatments improved retention, with Bent-6 retaining 15.6% water by day 12 (slope = −5.03), demonstrating the best performance in slowing water loss. Zeolite treatments improved retention compared to the control but were less effective than bentonite, with 6Zeo-6 retaining 14.7% water by day 12 (slope = −5.4) (Fig. 8a).

For DS2, the control showed the steepest decline (slope = −5.2), retaining only 8.8% water by day 12. Bentonite treatments significantly improved retention, with Bent-6 retaining 19.8%, the highest among all bentonite treatments. However, Zeo-6 outperformed bentonite, retaining 22.7% water by day 12, making it the most effective treatment. DS2 exhibited the highest water retention capacity, likely due to its higher clay content (Table 1).

For DS3, the control had the poorest retention, dropping to 1.2% by day 12, lower than the controls for DS1 and DS2. Among bentonite treatments, Bent-6 retained the most water (2.5%), though its decline rate was higher than lower concentrations. Zeolite treatments provided modest improvements, with Zeo-6 performing best, retaining 1.7% water by day 12.

Control treatments consistently showed the steepest declines in water content and the lowest retention (~ 1.2–8.9%) across all DSs, highlighting the poor water-holding capacity of untreated soils. Bent-6 was the most effective treatment, especially for DS2, retaining ~ 19.8% water by day 12. Zeolite treatments showed moderate improvements, with Zeo-6 retaining ~ 1.7% to 22.7% across DSs, performing best in DS2.

Discussion

Optimal treatment selection for enhancing soil crust properties across dust sources

The study results highlight the concentration-dependent effectiveness of bentonite, bentonite-sodium alginate, zeolite, and zeolite-sodium alginate in enhancing soil crust properties across three DSs around Lake Urmia. Higher concentrations (6%) consistently delivered the best results for crust thickness, mean compressive strength, and maximum compressive strength. Both bentonite and zeolite effectively improved soil crust properties, though their performance varied with DS characteristics, reflecting interactions between treatments and inherent soil properties (Figs. 9 and 10).

Fig. 9.

Heatmaps show the average performance of bentonite and zeolite treatments (2%, 4%, and 6%) across three dust sources. (a) Crust thickness (mm), (b) mean compressive strength (kPa), and (c) maximum compressive strength (kPa). Higher values indicate better performance in enhancing crust formation and soil strength.

Fig. 10.

Graphs showing the effects of bentonite, bentonite combined with sodium alginate, zeolite, and zeolite combined with sodium alginate treatments (2%, 4%, and 6%) on crust thickness (left column), mean compressive strength (middle column), and maximum compressive strength (right column) for DS1 (a–c), DS2 (d–f), and DS3 (g–i).

Bentonite treatments consistently outperformed other treatments across all DSs. DS2 showed the highest responsiveness to Bent-6, with crust thickness increasing by 15.22 mm compared to the control (Fig. 9a) and maximum compressive strength reaching 5632.03 kPa—an increase of 5260.42 kPa over Bent-0 (Fig. 10f). This suggests that DS2’s finer texture and higher clay content favored bentonite’s performance in improving crust properties. At intermediate concentrations (Bent-2 and Bent-4), DS2 also exhibited strong and progressive improvement: crust thickness and strength increased almost linearly, with Bent-4 already producing more than a 10 mm gain in thickness and strength exceeding 3000 kPa. This confirms that even moderate additions of bentonite substantially enhance DS2 stability, while Bent-6 simply amplifies this trend.

In DS1 and DS3, Bent-4 and Bent-6 also provided significant improvements, forming stable and uniform crusts. In DS1, Bent-2 produced only modest gains, whereas Bent-4 generated a much clearer improvement in both thickness and strength, highlighting a threshold-like response where DS1 begins to benefit substantially only above 4% bentonite. Similarly, DS3 showed a steady increase from Bent-2 to Bent-4 and finally to Bent-6, indicating an incremental and consistent strengthening pattern across concentrations. However, compressive strength exhibited higher variability (16.88%; see Table S3 in the Supplementary file), likely due to differences in soil composition and strength properties. These findings confirm bentonite’s consistent ability to enhance soil crust strength and stability, particularly at higher concentrations.

The superior performance of bentonite can be attributed to its high swelling capacity and very fine particle size, which enhance interparticle bonding and modify the pore structure of the soil matrix. Previous studies have shown that bentonite can significantly improve soil stability by increasing cohesion and strengthening particle contacts. For instance, Bani Baker et al.³⁹ reported that small additions of bentonite slurry substantially increased the shear strength and structural stability of sandy soils due to its cohesive nature and ability to bind particles together. Microstructural investigations further indicate that bentonite can coat soil grains and progressively fill pore spaces as its content increases, thereby reducing void connectivity and forming a denser structure³⁸. In addition, Wong et al.⁵³ demonstrated that sodium bentonite contributes to pore refinement and stronger interparticle bonding through filler and pozzolanic effects, resulting in higher cohesion and reduced permeability in stabilized soils. These mechanisms provide an explanation for the substantial increases in crust thickness and compressive strength observed in the present study, particularly in DS2 where the finer soil texture likely promoted better bentonite hydration and particle bonding.

The incorporation of sodium alginate into bentonite treatments introduced complexity. While it enhanced crust stability in weaker soils like DS3, it generally resulted in thinner, less compressive crusts compared to bentonite alone. For instance, in DS1, maximum compressive strength dropped from 2577 kPa with bentonite to 653.15 kPa with bentonite–sodium alginate (Fig. 9c). This reduction was attributed to increased pore size and uneven alginate distribution. Intermediate concentrations (Bent-SA-2 and Bent-SA-4) further clarified this trend: in DS1 and DS2, increasing alginate content did not improve strength proportionally, and both soils showed irregular or even declining performance at 4%, suggesting that the polymer interferes with optimal mineral bonding at these levels. However, sodium alginate improved crust stability at lower bentonite levels, particularly in DS3, where Bent-SA-6 achieved compressive strengths comparable to bentonite alone. Variability in crust thickness and compressive strength increased from 5.95% to 10.57% and 16.88% to 24.28%, respectively (Table S4 in the Supplementary file), indicating challenges in optimizing sodium alginate distribution.

Sodium alginate has been widely reported to improve soil stability by promoting particle flocculation and forming polymeric bridges that fill pore spaces and increase aggregate size^45,46,54. However, in mixed mineral–polymer systems, the distribution of the polymer and its interaction with mineral particles can strongly influence pore structure and bonding, which may explain the reduced crust thickness and compressive strength observed in some bentonite–sodium alginate treatments in the present study.

Zeolite treatments showed moderate effectiveness, especially in DS2, where the Zeo-6 increased crust thickness by 10.11 mm and reached a maximum compressive strength of 3705.55 kPa (Fig. 10f). Though zeolite-treated crusts were thinner than bentonite-treated ones, their compressive strength at 6% was comparable in DS2. At 2% and 4%, DS2 again showed a coherent and graded response: Zeo-2 generated measurable but limited improvements, while Zeo-4 produced a clear increase in thickness and mechanical strength, indicating that intermediate doses can still induce effective structural enhancement in soils rich in clay and silt. However, DS1 and DS3 showed less improvement, with the 6% treatment achieving thicknesses of 6.35 mm and 7.03 mm, respectively (Fig. 10a, g). The intermediate Zeo-2 and Zeo-4 levels in DS1 and DS3 produced shallow or inconsistent trends, reinforcing that zeolite is less effective in coarser or carbonate-rich soils at moderate concentrations. Zeolite exhibited lower strength variability (10.34%) than bentonite, providing consistent stabilization but limited thickness gains (Table S5).

Adding sodium alginate to zeolite treatments produced mixed outcomes. In DS2, strength decreased from 3705.55 kPa to 1537.88 kPa in Zeo-SA-6 (Fig. 10f), while in DS1 and DS3, it improved crust thickness and strength. At the intermediate levels (Zeo-SA-2 and Zeo-SA-4), DS1 and DS3 showed modest but noticeable improvement in crust structure, although still lower than mineral-only treatments. In DS2, however, Zeo-SA-2 and Zeo-SA-4 performed markedly worse than Zeo-2 and Zeo-4, indicating that the combination disrupts the packing and bonding efficiency in finer-textured soils. For instance, in DS3, Zeo-SA-6 increased thickness by 8.5 mm over the control, reaching 1202.40 kPa mean strength (Fig. 10g, h). However, in DS1, average crust thickness dropped from 6.55 mm to 3.94 mm (Fig. 9a).

In conclusion, bentonite proved most effective, particularly in finer soils like DS2, offering superior crust thickness and strength. The analysis of intermediate concentrations (2% and 4%) across all DSs clearly shows that bentonite produces a predictable and cumulative improvement pattern, with DS2 responding strongly even at low levels, and DS1 and DS3 benefiting substantially once concentrations exceed 4%. Sodium alginate benefited weaker soils but introduced variability and occasional strength reductions. Zeolite showed moderate effectiveness, mainly in DS2, while zeolite–sodium alginate was inconsistent across sources. Tailoring treatments to soil properties and optimizing additive distribution are crucial for effective stabilization. Future research should explore bentonite–zeolite synergies and improve sodium alginate distribution for more uniform crust formation.

Insights into structural and compositional modifications

Figure 11 presents FTIR spectra for control, bentonite-treated, and zeolite-treated samples, providing insights into chemical and structural changes induced by the treatments. These findings are essential for understanding the impact of bentonite and zeolite on dust sources and their implications. The control spectrum serves as a baseline, showing dominant silicate minerals (Si–O bending at 400–600 cm⁻¹, Si–O-Al bands at 456–518 cm⁻¹, and Si-(Al)-O stretch at 1000–1100 cm⁻¹), carbonate minerals (C-O stretch at 1438 cm⁻¹), and hydroxyl groups (O–H stretch at 3500–3600 cm⁻¹), typical of mineral soils. The spectra for DS1, DS2, and DS3 displayed similar trends, with silicates, hydroxyl groups, and carbonates present across all sources. However, variations in band intensity and shape were noted, indicating differences in DS characteristics and treatment interactions.

Fig. 11.

FTIR spectra of DS1, DS2, and DS3 under different treatments. (a) DS1; (b) DS2; (c) DS3. Each panel compares the spectral transmittance (%) for the control, bentonite-treated (6%), and zeolite-treated (6%) samples. Key functional group regions are highlighted: Si–O-Al or Mg(OH) (600–800 cm⁻¹), Si(Al)-O stretch (1000–1100 cm⁻¹), C-O stretch (calcite/dolomite) (1400–1500 cm⁻¹), and O–H stretch in clay minerals (3000–3600 cm⁻¹). The spectra are plotted with decreasing wavenumbers, emphasizing differences in mineral and surface chemistry across treatments.

Importantly, the region around 1600–1700 cm⁻¹, where the H–O–H bending vibration of absorbed water (~ 1640 cm⁻¹) typically appears, is not expressed as a distinct peak in any of the samples. This is mainly due to overlap with broad aluminosilicate combination bands and carbonate absorptions that mask the bending mode of molecular water. However, when this region is magnified, slight increases in absorbance between the control and treated samples become visible, particularly in DS2, which has higher clay content and therefore greater inherent water-retention capacity.

In addition, several weak bands are visible in DS1 between the Si–O/Si–O–Al region and the Si–O–Si/Al(Mg)OH region, whereas they are much less pronounced in DS2 and DS3. These features correspond to carbonate phases—especially aragonite—which is abundant in DS1⁵². The ν₂ and ν₄ vibration modes of aragonite (approximately 700–720 and 850–880 cm⁻¹) partially overlap with silicate-related bands, producing the additional shoulders observed in DS1.

Effects of bentonite addition

Bentonite treatment induced significant spectral changes, particularly in hydroxyl, silicate, and aluminosilicate regions. The O–H stretching region (3500–3600 cm⁻¹) showed broader and more intense peaks compared to the control, indicating bentonite’s hydration properties and its enhanced water retention capability. This aligns with bentonite’s hydrophilic nature, improving the dust source’s moisture retention.

In DS1 (Fig. 11a), the intensity of the O–H stretching region increased after bentonite addition, reflecting the hydrophilic layered structure of bentonite. Although the H–O–H bending peak at ~ 1640 cm⁻¹ is not clearly resolved, enlargement of this region shows subtle differences between the control and treated samples, supporting the expected increase in moisture retention. In DS2, the control sample already displayed strong O–H-related absorption due to its higher clay content, and bentonite addition further enhanced this trend. DS3 showed a similar response, though with smaller changes due to its coarser texture.

Bentonite treatment also increased absorbance in the Si(Al)–O stretching region (1000–1100 cm⁻¹) and the Si–O–Al region (456–518 cm⁻¹), indicating enrichment of aluminosilicate phases. In DS1 and DS3, these bands became sharper and more intense following treatment. In DS2, however, the initially high clay content resulted in stronger silicate absorption in the control sample than in the treated ones, making the treatment effects less pronounced in this source.

Effects of zeolite addition

Zeolite-treated samples exhibited spectral changes reflecting the unique properties of zeolites. The Si-(Al)-O stretch (1000–1100 cm⁻¹) showed intensified peaks, similar to bentonite in DS1 and DS3. In DS 2, where the control had stronger absorption, zeolite treatment outperformed bentonite (Fig. 11b). The O–H stretching region (3500–3600 cm⁻¹) displayed broad peaks in DS3, indicating zeolite’s water retention, though its hydration capacity may vary across sources.

The Si–O-Al band (456–518 cm⁻¹) increased in intensity for zeolite-treated samples, but with broader peaks than bentonite, reflecting zeolite’s rigid framework and lower reactivity. In DS1, zeolite-treated samples showed strong Si-(Al)-O stretching peaks, slightly broader and shifted compared to bentonite. Similarly, DS 3 exhibited distinct Si–O-Al bands, but with lower intensity than bentonite (Fig. 11c).

While FTIR spectra reveal structural changes induced by bentonite and zeolite, they do not fully explain the enhanced stability observed in DS2. The high clay content in the control sample may have overshadowed treatment-induced spectral changes. Further analysis using Field Emission Scanning Electron Microscopy (FESEM) was conducted to explore morphological and structural changes resulting from the treatments.

Morphological analysis of Dust Sources using FESEM

Figure 12 presents FESEM images illustrating the morphological changes in control and treated DSs, highlighting the effects of the applied treatments. Selected treatments were based on their superior performance in crust stability and compressive strength. For DS1, Bent-6 was chosen for its thicker crusts and highest compressive strength. In DS2, Zeo-6 was selected for its comparable strength to bentonite, thicker crust formation, and superior water retention. For DS3, Bent-SA-6 was analyzed due to its comparable performance to bentonite alone.

Fig. 12.

FESEM images of the three dust sources under their selected optimal treatments. (a), (e), and (i) show the control samples of DS1, DS2, and DS, respectively. (b), (c), and (d) present DS1 treated with bentonite (6%) at increasing magnifications, selected due to its superior crust thickness and highest compressive strength. (f), (g), and (h) display DS2 treated with zeolite (6%) at increasing magnifications, chosen for its comparable strength to bentonite and its enhanced crust formation and water retention. (j), (k), and (l) illustrate DS3 treated with bentonite (6%) combined with sodium alginate (0.5%) at increasing magnifications, selected for its comparable performance to bentonite alone.

Control samples of DS1, DS2, and DS3 exhibited loose, poorly connected particles. DS1 (Fig. 12a) displayed loosely packed, angular particles with minimal adhesion. DS2 (Fig. 12e) showed a more compact structure but weak bonding. DS3 (Fig. 12i) revealed a granular structure with visible voids, aligning with the lower stability observed in untreated samples. Bent-6 treatment of DS1 (Fig. 12b–12d) showed interconnected particles, with bentonite acting as a binder to enhance cohesion and form a denser, stable crust, correlating with improved compressive strength.

Zeo-6 treatment of DS2 (Fig. 12f, 7h) demonstrated enhanced aggregation and increased porosity. Zeolite particles filled voids and improved bonding, forming stable aggregates that enhanced soil stability and water retention. The increased pore spaces facilitated moisture absorption and storage, supporting zeolite’s dual role in stabilization and water retention. Despite the control sample’s higher clay content, zeolite treatment achieved comparable strength and superior water retention.

Bent-SA-6 in DS3 (Fig. 12j–12l) resulted in a denser, well-bonded crust. Sodium alginate enhanced bentonite’s binding capability, contributing to improved stability and strength, aligning with compressive strength results. FESEM analysis confirmed significant morphological improvements across treatments, with bentonite excelling in DS1, zeolite enhancing DS2’s stability and water retention, and the combined treatment showing promise for DS3. These findings complement FTIR results and offer deeper insights into treatment-induced structural changes.

Comparative evaluation of amendment performance

To better interpret the effectiveness of the tested amendments, the results of this study were compared with previous investigations conducted on the dust hotspots and playa surfaces of Lake Urmia. The findings show that the four amendments—bentonite, zeolite, bentonite combined with sodium alginate, and zeolite combined with sodium alginate—affected soil crust development differently across the three dust hotspots. Bentonite consistently produced the thickest and strongest crusts, particularly in DS2, where Bent-6 increased crust thickness by more than 15 mm and generated compressive strengths approaching 6000 kPa. These improvements reflect bentonite’s strong swelling and binding capacity, supported by the finer texture and higher clay content of DS2, which favor mineral hydration and particle bonding. Zeolite, although beneficial in all soils, produced thinner and mechanically weaker crusts, likely due to its rigid framework structure and limited swelling capacity compared with bentonite.

A clearer interpretation emerges when the results are compared with previous studies on natural crusts around Lake Urmia. The clay-flat (CF) and clay-flat–salt-crust (CF–SC) surfaces reported by Hamzehpour and Marcolli¹² represent the most stable natural crusts in the region, with thicknesses of about 2 cm and compressive strengths of 6700–7400 kPa. Although the bentonite-induced crusts in this study did not fully reach these strength levels, their values—especially in DS2—approached the lower range. Moreover, bentonite formed deeper and more uniform crusts than previously reported natural sand-sheet crusts, suggesting that it can partially replicate the structural conditions of stable CF-type surfaces. Zeolite, in contrast, showed performance closer to sand-sheet crusts, providing reinforcement but lacking sufficient depth and mechanical uniformity.

Comparisons with chemical stabilizers used in other studies also help clarify the relative performance of the amendments tested here. Alkhayer et al.²¹ showed that Mg-enriched brines can quickly generate strong crusts by precipitating halite and bischofite. However, their crusts tended to be shallow and brittle, with strength concentrated near the surface. The bentonite-induced crusts in the present study formed more cohesive layers that maintained strength across depth, particularly in DS2 and DS3. Although Mg-brine reduced soil loss effectively, the internal uniformity of bentonite crusts suggests that mineral-based stabilization may be more suitable for conditions requiring longer-term mechanical resilience. Zeolite’s performance relative to Mg-brine is particularly notable in DS2, where the Zeo-6 treatment reached strengths (≈3700 kPa) comparable to those reported for Mg-brine treatments. However, the thinner crusts produced by zeolite emphasize that, while chemically stable, zeolite does not enhance crust thickness or depth-related strength as effectively as bentonite.

The results from Bahmani et al.²³ add an additional layer of comparison by demonstrating that SC-brine treatments generate strong crusts in sandy, quartz-rich soils (DS3), with maximum strengths exceeding 4900 kPa. Although this strength is comparable to or even higher than some of the bentonite results in DS3, SC-brine remained less effective in DS1 and DS2, where maximum strengths remained below 1300 kPa. By contrast, bentonite produced consistently strong crusts across all soils in the present study. These differences emphasize that salt-based crusts rely heavily on mineral precipitation patterns, which vary across soils, while bentonite’s performance depends more on its intrinsic swelling and binding properties, making it less sensitive to soil texture and mineralogy. Zeolite, on the other hand, showed an intermediate behavior: its performance in DS2 exceeded SC-brine, while in DS1 and DS3 it remained lower than both SC-brine and bentonite. This suggests that zeolite stabilization—much like SC-brine—is highly dependent on soil texture, performing best in fine-textured soils but losing effectiveness in carbonate-rich or quartz-dominated systems.

A notable contrast emerges when comparing the present findings with the sodium alginate-based crusts reported by Hamzehpour et al.⁵². In that study, sodium alginate alone achieved thick, highly resistant crusts on DS1 soils, particularly under compaction. However, when combined with bentonite or zeolite in the current study, crust strength in DS1 and DS2 decreased significantly. This disparity reflects two distinct stabilization mechanisms: alginate acts as a surface-binding polymer that is most effective in clay- and salt-rich soils, whereas bentonite and zeolite rely on mineral hydration and physical particle packing. The integration of alginate with these minerals appears to result in a viscous gel that hinders mineral interlocking and increases porosity, thereby reducing overall strength. Nevertheless, the bentonite–alginate mixture offered distinct advantages in DS3, where the polymer enhanced strength throughout the deeper layers. In contrast, zeolite–alginate mixtures performed most poorly, indicating that zeolite’s limited swelling capacity and rigid structure render it particularly sensitive to the pore-enlarging effects of the alginate gel.

Taken together, these comparisons indicate that bentonite is the most versatile and reliable amendment for stabilizing dust-source soils around Lake Urmia. Its ability to increase crust thickness and strength across all DSs, combined with sustained strength with depth, distinguishes it from both polymer-based and salt-based stabilizers. Zeolite, although clearly beneficial, exhibited a lower overall strengthening capacity and produced thinner crusts, suggesting that it may function better as a supplementary amendment rather than a primary stabilizer. Sodium alginate, while promising under certain conditions, introduced variability when combined with mineral amendments and was mainly effective in coarse-textured soils where mineral-based treatments alone were less effective.

Overall, the collective evidence suggests that bentonite offers the closest engineered approximation to naturally stable playa crusts. Zeolite contributes meaningfully to crust formation—especially in DS2—but cannot alone match the depth stability and mechanical strength achieved by bentonite. Its performance across three contrasting soil types reinforces bentonite’s potential as a primary material for dust mitigation strategies on desiccated lakebeds such as Lake Urmia. Future work should explore whether combining bentonite with zeolite or optimizing the layering of polymer applications can further enhance crust uniformity while maintaining high strength, especially in soils with challenging textures like DS1 and DS3.

Conclusion

• This study evaluated the effectiveness of bentonite, zeolite, and sodium alginate as sustainable soil-stabilizing amendments for dust-prone playa soils surrounding Lake Urmia.

• Bentonite demonstrated the most consistent performance across all dust sources, with the 6% application rate producing the thickest crusts and the highest mechanical strength.

• Zeolite produced moderate improvements overall, with its strongest performance in Dust Source 2, where the finer soil texture and mineral composition allowed the formation of crusts with strength levels approaching those of the bentonite treatments.

• The combined bentonite–sodium alginate treatment enhanced crust formation in Dust Source 3, particularly at lower bentonite concentrations, although reductions in compressive strength were observed in some soils due to increased heterogeneity in crust development.

• FTIR analysis identified the functional groups and surface-level mineral interactions associated with enhanced cohesion, while FESEM imaging provided clear evidence of the resulting microstructural changes, including denser particle arrangements and improved bonding.

• Notably, the enhanced stability observed in Dust Source 2 could not be fully explained by FTIR spectra alone and is likely related to its finer texture and higher clay content, as supported by FESEM morphological observations.

• Bentonite is the most effective amendment for coarse- to mixed-textured soils, while zeolite may offer advantages in fine-textured soils where structure and mineral composition favor its interaction with the soil matrix.

• The results highlight the need for site-specific selection of stabilizing agents, as soil texture and mineralogy strongly influence treatment performance.

Future research directions

• Assessing long-term field-scale performance of these treatments under natural wetting–drying cycles and wind erosion conditions.

• Exploring the economic and environmental feasibility of large-scale application in arid and semi-arid regions facing severe dust emission challenges.

• Evaluating the effects of these amendments on soil microbial activity and ecological recovery in degraded playa environments.

Author contributions

Saeed Pourmohammad and Hossein Bahmani: Conducted the lab experiments and field work and manuscript preparation; Nikou Hamzehpour : Contributed to field work; research design, lab experiments; interpretation of the experiments writing-review and editing; Seyed Bahman Mousavi and Maryam Moosavifar : contributed to research design, lab experiments, and analysis.

Data availability

Data will be provided on request.

Declarations

Competing interests

The authors declare no competing interests.