Application of Humate-Containing Agent for Sorbing Trace Metals in Simulated Solutions and Surface Waters from Tunnels at the ‘Degelen’ Site

Abstract

This article presents the potential use of a humic agent called ‘Superhumate’, obtained from weathered coal from the Shubarkol deposit in Kazakhstan. The experiment was conducted using model solutions and surface mine water samples from the “Degelen” site at the Semipalatinsk Test Site. The adsorption of heavy metals and toxic elements using the “Superhumate” agent was carried out under dynamic conditions using a chromatographic column. Tests were conducted at a natural pH range of 5–8 (mine waters) and with a model solution at pH 1.7. Assessing the sorption efficiency of this preparation revealed that at pH 1.7, the agent does not adsorb elements such as Cd, Cu, Pb, and Zn. Under dynamic experimental conditions, using the preparation for mine waters at natural pH levels (pH 5–8), elements such as Be, Sr, Mo, Cd, Cs, Zn, and U were efficiently adsorbed at levels of 60–95%. The sorption efficiency of Pb ions was found to be almost independent of pH. The experimental results obtained with mine water samples indicate that alkaline solutions have the highest sorption efficiency, with pH ≥ 7, which is attributed to the solubility of the agent.

1. Introduction

From 1949 to 1989, nuclear tests were conducted at the Semipalatinsk Test Site (STS), leaving a profound imprint on Kazakhstani history [1]. Both aboveground and underground tests resulted in significant ecological damage and adversely affected human health [2]. Environmental and human health protection against exposure to residual and secondary radioactivity is a key aspect in solving test site problems. To date, several decisions have been made to carry out planned work aimed at returning radioactively contaminated areas to economic use [3]. This was supported by the RK’s Security Council on 6 April 2009 and by the Protocol Decision of the Interdepartmental Commission affiliated with the RK’s Security Council on 7 May 2009, as well as by the programme for comprehensive solutions to the challenges at the former Semipalatinsk Nuclear Test Site for the 2005–2007 period [4]. Additionally, on 5 July 2023, a new law was adopted in the Semipalatinsk Nuclear Safety Zone, aiming to rehabilitate the territory of the former Semipalatinsk Nuclear Test Site [5]. According to the RK’s legislative acts, the entire STS territory is currently categorized as reserve land [6]. Pursuant to cl. 143 of the ‘RK’s Land Code’, ‘Land plots at which nuclear tests were conducted, cannot be transferred by the RK’s government into the ownership or land use until after all nuclear remediation activities and the comprehensive ecological survey are complete, if a positive state ecological expert examination is granted’ [7,8]. Overall, the main potential mechanisms of radionuclide migration from nuclear test locations are via air and water [9,10,11,12]. Thus, a crucial point in ensuring radiation safety and ecological sustainability in the region is to develop surface water treatment techniques.

Research indicates that the sustainable management of water resources through various adsorption and remediation methods remains a highly pertinent and significant issue [13,14,15]. Adsorption is a popular technique for treating wastewater and natural water thanks to its cost-effectiveness and ease of use. Humate-containing products, with high sorption capacity and good ion exchange properties, can substitute costly synthetic reagents in the treatment of contaminated water. At the same time, one should note that humic acids (HAs) and their decay products, based on their chemical properties, are not toxic with respect to environmental compartments [16].

JSC ‘A.B. Bekturov Institute of Chemical Sciences’ has developed technology for producing an eco-friendly humate-containing agent from natural raw materials of the Republic of Kazakhstan. A trademark for the preparation “Superhumate” has been obtained [17].

This paper aims to define the sorption efficiency of this agent with respect to toxic elements (TEs) and trace metals (TMs) using a combination of simulated solutions and tunnel surface waters from the ‘Degelen’ site of the Semipalatinsk Test Site, as well as to assess a pH medium’s impact on the agent’s sorption capacity.

2. Materials and Methods

2.1. Description of Test Objects

To research the efficiency of this agent, two types of samples were selected—natural surface waters from the ‘Degelen’ site and simulated solutions prepared in the laboratory.

2.1.1. Surface Waters

To assess the efficiency of a humic agent in situ, tunnels were chosen based on the characterization of a pH medium’s impact on the agent’s sorption capacity because humic acids are alkali-soluble and acid-insoluble (at pH < 2) [18]. To compare the agent’s sorption capacity under different pH conditions, tunnels with slightly acidic, neutral, and slightly alkaline environments were chosen.

Surface waters in the following tunnels were chosen as research objects: 104, 165, 176, 504, and 511. These tunnels are characterized by high contents of TEs, TMs, and radionuclides. For example, water samples from tunnel 504 exhibited abnormally high concentrations of rare earth elements (REEs)—which were up to 1000 times their typical concentrations found in groundwater from arid climates—as well as some heavy metals and toxic elements such as Be, Zn, and Pb, exceeding their maximum permissible concentrations (MPCs) [19,20,21]. One should note that the selected tunnels are characterized by steady water streams throughout the year (Figure 1 and Figure 2).

2.1.2. Simulated Solution Preparation

To prepare a 200 mL simulated solution, a state reference standard of studied metals was used. The solution was made up to the volume of 1% with nitric acid (pH = 1.7) at room temperature. The simulated solution was used together with tunnel waters to assess the difference in the sorption effect of the humate-containing agent under controlled and natural conditions.

2.2. The Preparation of a Modified Humate-Containing Agent

The agent ‘Superhumate’ (hereinafter referred to as ICS-3A) is made of humic acids that do not dissolve in acids but are alkali-soluble. This agent was obtained from weathered coal of the Shubarkol deposit (Karaganda region) using 2% NaOH (1:8 weight-to-volume ratio) for 1 h at 25 °C while rapidly mixing and precipitating it by adding muriatic acid until reaching pH 1–2. The residue was filtered, flushed in distilled water to achieve a negative reaction to chloride ion, and dried in an oven at 70–80 °C.

Chemical analysis techniques were used to determine the contents of free humic acids [22], ash [23], and moisture [24]. The number of carboxyl groups and phenolic hydroxyls was determined using a combination of techniques based on calcium acetate and barium sulfate [25,26].

2.3. Experimental Conditions

The sorption experiment with ICS-3A was conducted under dynamic conditions in a glass chromatographic column set vertically. Water samples collected from tunnels, without filtering, were stored in air-tight containers. Two types of chromatographic columns which were 0.8 and 1.0 cm in diameter at the tapered part were used. The work solution was passed though the columns. It took 72 h for the solution to pass through the sorbent at a small diameter (0.8 cm), whereas at a large diameter (1.0 cm), it took 48 h.

The volumetric flow rate of liquid through a chromatographic column is calculated considering the cross-sectional area of the column, the column height, and the linear flow rate.

A = π·(d/2)²,

(1)

Thus, in column 1, the volumetric flow rate is ≈1.04 mL/h (diameter 1.0 cm).

In column 2, the volumetric flow rate is ≈0.69 mL/h (diameter 0.8 cm). The possible influence of the column’s parameters on the sorption kinetics should be considered.

A cotton swab was placed in the lower tapered part of the column, and then the agent was poured. The ratio of S (solid) to L (liquid) must be 1:50, i.e., 1 g of the sorbent per 50 mL of the solution. Under dynamic conditions (a flowing system), it takes 48–72 h for 50 mL of the contaminated water to pass through this agent in the columns, representing the experimental flow rate. Waters exiting the columns were collected and held for subsequent chemical analyses.

The adsorption efficiency (R%) is computed from the difference in the original concentration of metal ions (Me) in the solution and following the sorbent interaction:

R% = [(C₀ − C_p)/C₀] × 100,

(2)

where C₀ and C_p represent the initial and equilibrium concentrations of metal ions, %.

2.4. Determination of Organically Bound Carbon in Water

The determination of organically bound carbon in the water allows for the estimation of the agent water resistance. This property consists of treating water with an oxidizer, K₂Cr₂O₇, in a H₂SO₄ solution over a catalyst, Ag₂SO₄. To reduce the hampering effect, HgSO₄ was added to anion chloride. Following sample mixing with the above reagents, the resulting mixture was heated in the oven. The final content of organically bound carbon was determined by photocolorimetry [27,28,29].

Organically bound carbon was measured with a PE-5400 V spectrophotometer with a wavelength of 440 nm. Calibration was based upon the Na₂C₂O₄ 0.005 M mixture diluted to obtain carbon-containing solutions: 2.4, 4.6, and 9.6 mg/dm³.

2.5. Determination of Elemental Composition of ICS-3A Agent

ICS-3A was decomposed according to previous guidelines [30] and the operating instructions RI 03-02-03 (A): ‘Sample preparation for the elemental analysis by autoclave digestion’ [31,32]. An ICS-3A subsample of 0.5000 ± 0.0001 g was placed in the autoclave fluoroplastic insert, wetted using 1 mL of H₂O, and added to 6 mL of conc. HNO₃ and 1 mL of 30% H₂O₂. After 40 min, the fluoroplastic insert was lidded and inserted in the autoclave’s outer case and then in the steel bed with a clamping device. The bed with the autoclave was placed in an oven heated to 160 ± 5 °C and aged for 2.5 h. Upon completion of autoclaving, a cooled sample was quantitatively transferred to a volumetric test tube and made up to a volume of 15 cm³ with 1% nitric acid. The resulting solution was diluted in a 1% HNO₃ solution in a ratio of 1:10 and assayed for elements of interest.

2.6. Analytical Activities

The initial and equilibrium concentrations of metal ions in the solutions were determined by inductively coupled plasma mass spectrometry and atomic emission spectrometry using instruments Agilent 7700 made by ‘Agilent Technology’ (Santa Clara, CA, USA) and iCAP 6300 Duo made by ‘Thermo Scientific’ (Waltham, MA, USA). These techniques were used to determine around 20 elements, namely Be, Al, Cu, Zn, Sr, Fe, Mo, Cd, Cs, La, Ce, Pr, Nd, Sm, Eu, Gd, Dy, Yb, Th, and U, with detection limits of 0.01–100 µg/dm³ and 10–15% uncertainty. Macroelements (Al and Fe) were predominantly determined by ICP-AES.

A multi-element reference solution of a reference sample (RS) containing metals made by Inorganic Ventures (IV-ICPMS-71A, Christiansburg, VA, USA) was used for calibration graphs. The measurement quality was overseen by measuring the calibrating solution every 10 samples. To prepare samples for accuracy (validity) control of the calibrating characteristics, an RS containing metals made by Perkin Elmer (No. 9300233, Waltham, MA, USA) and CMS-1 (Inorganic Ventures, CIIIA) were used. After obtaining a poor calibration result (deviation from the calibration graph by 8–10%), the instrument was recalibrated considering new background parameters.

The analysis was carried out as per the procedure ISO 17294-2: 2003: (E) ‘Water quality. Application of inductively coupled plasma mass spectrometry (ICP-MS)’ [33].

3. Results

3.1. The Characteristics of a Sorbent and Natural Waters Employed in the Experiment

3.1.1. Elemental Composition of ICS-3A Agent

The chemical composition of the ICS-3A agent obtained from weathered coal of the Shubarkol deposit is shown in the table below (

Table 1. Gross elemental composition of ICS-3A.

Elements	Mass Fraction, %
C	42.00
H	3.00
O	31.00
N	1.30
Al	0.062
Fe	0.36
Zn	0.0021
Sr	0.001
Mo	0.003
Cd	0.000007
Cs	0.0000044
∑ REE 1	0.00019
Pb	0.00093
U	0.0057
HAdaf	82.0
Wa	10.0
Aa	18.0
COOH (mmole/g)	1.18
ONfen (mmole/g)	1.69

¹ ∑ REE—La, Ce, Pr, Nd, Sm, Eu, Gd, Dy, Er, Yb. HA^daf—yield of free humic acids; W^a—moisture; A^a—ash content.

).

The ultimate elemental composition of humate-containing agents depends on the original raw material and the selected manufacturing procedures used in the agent formulation. The sorbent obtained from the Shubarkol deposit is primarily composed of organic matter (82%). The ash content of this sorbent at 20% proves the presence of various mineral substances. As is seen from the table, the mineral composition is attributed to such elements as Fe and Al (0.36% and 0.062%), whose oxides are known sorbents to metals and metalloids.

3.1.2. Features of the Chemical Composition of Surface Waters from Tunnels 104, 165, 176, 504, and 511

A general chemical analysis of water samples allows for the assessment of the specific nature of the ICS-3A agent’s behaviour and the sorption efficiency of elements under various natural medium conditions (pH levels, salinity, etc.). The results of the general chemical analysis of water samples collected from tunnels of the ‘Degelen’ site are listed in

Table 2. Research findings of the general chemical analysis of water from tunnels 104, 165, 176, 504, and 511, mg/dm³.

Tunnel	Hardness (mmole/dm3)	pH	Content of Cations			Content of Anions			Salinity
			Na++ + K++	Ca2++	Mg2++	Cl−	HCO3−	SO42−
104	4.5	7.8	3	40	30	25	55	145	265
165	4.7	8.0	6	40	30	95	50	70	265
176	2.3	7.7	2	30	9	25	45	45	130
504	7.5	5.6	30	80	40	10	75	350	540
511	3.0	6.8	15	50	10	10	50	125	225

.

Waters from tunnel stream flows have various chemical compositions and differ from one another. The water pH level varies from slightly acidic at 5.6 (tunnel 504) to slightly alkaline at 8.0 (tunnel 165). The content of organically bound carbon in the water is below 1 mg/dm³. The water salinity type and hardness vary with the water stream flow:

Tunnel 104—type SO₄²⁻–Mg²⁺⁺; subsaline, hard water.

Tunnel 165—type Cl⁻–Mg²⁺⁺; subsaline, hard water.

Tunnel 176—type SO₄²⁻–Mg²⁺⁺; subsaline, hard water.

Tunnel 504—type SO₄²⁻–Ca²⁺⁺; subsaline, hard water.

Tunnel 511—type SO₄²⁻–Ca²⁺⁺; subsaline of normal hardness.

On average, waters of tunnel stream flows have a sulphate base with predominant calcium and magnesium cations.

For a detailed study of ion composition features, a Piper diagram was constructed (Figure 3), which highlights the primary geochemical facies relying on the content of dominating anions and cations.

Waters in the Piper diagram refer to the sulphate saline facie dominated by Ca²⁺ and Mg²⁺. One may conclude from the diagram analysis that the tunnel water composition is formed by processes of mineral leaching from water-bearing rocks and the oxidation of sulphide minerals. As these water stream flows are steady all year round, the effect of evaporating concentration processes is poor.

Features of the chemical composition of tunnel surface waters based on the Piper diagram are as follows:

• Tunnel 104—sulphate slightly alkaline and hard waters dominated by magnesium in the water;
• Tunnel 165—chloride slightly alkaline and hard waters dominated by magnesium in the water;
• Tunnel 176—sulphate slightly alkaline and hard waters dominated by calcium in the water;
• Tunnel 504—sulphate slightly acidic and hard waters dominated by calcium and magnesium in the water;
• Tunnel 511—sulphate neutral waters of normal hardness dominated by calcium in the water.

With respect to the chemical composition, the studied waters differ in pH, salinity, hardness level, and dominant cations. In view of the above differences, the pattern of trace element sorption by the ICS-3A agent may vary.

3.1.3. Variation Dynamics of Organically Bound Carbon in the Water

To reveal any features of variations in organically bound carbon in the water, a spectrophotometric analysis was carried out.

Table 3. Averaged contents of organically bound carbon in the water of tunnel water stream flows at the ‘Degelen’ site following the application of ICS-3A, mg/dm³.

No.	Tunnel	Carbon Content, mg/dm3
Dynamic conditions
1	104	6.3
2	165	5
3	176	7
4	504	1.3
5	511	6.3

lists the results of the water analysis of tunnels at the ‘Degelen’ site for organically bound carbon following the application of this sorbent.

No organically bound carbon was detected in any specified water samples collected from the ‘Degelen’ site, but following the application of humic agents, the content of organically bound carbon in the water increased from 1 mg/dm³ to 7 mg/dm³. Differences in the content of organically bound carbon following the application of this agent are attributable to the pH value. For example, the agent water solubility in the acidic medium (pH 5.6) is lower (1.3 mg/dm³) than in the alkaline medium (7 mg/dm³).

3.2. Application of Sorption Material to Purify Simulated Solutions

To assess ICS-3A’s sorption capacity, a simulation experiment imitating water contamination by some HM ions (Cd²⁺-23 mg/dm³, Cu²⁺-25 mg/dm³, Pb²⁺-25 mg/dm³, and Zn²⁺-25 mg/dm³) was conducted under dynamic conditions. A comparative analysis of data on agent utilization in a simulated solution is presented in

Table 4. The results of the experiment with a simulated solution (n = 3, pH 1.7).

	Cd, mg/dm3	Cu, mg/dm3	Pb, mg/dm3	Zn, mg/dm3
Simulated solution	23 ± 2	25 ± 2	25 ± 2	25 ± 2
Following ICS-3A application	30 ± 3	27 ± 3	29 ± 3	33 ± 3

.

The data obtained from the simulated solution demonstrate that at a low pH of 1.7, the agent does not sorb such elements as Cd, Cu, Pb, and Zn. This is because at pH = 2–3, humic acids return to their original state, resulting in an insoluble phase in the form of colloids, which coagulate, and gel-like precipitates are created. pH values around 2–3 correspond to the coagulation point at which irreversible coagulation of the colloids and polymerization of humic acid molecules occur. This process blocks their reactive centres, significantly reduces the surface area of phase separation, and decreases their physicochemical and biological activities [33].

At low pH values, heavy metal ions such as Cu²⁺⁺, Pb²⁺⁺, and Cd²⁺⁺ predominantly exist in their free and soluble forms and do not precipitate as insoluble hydroxides. As the pH increases—typically above 5–6—these metal ions begin to precipitate in the form of hydroxides, thereby decreasing their availability for sorption processes. Under alkaline conditions, metal ions may undergo hydrolysis, resulting in the formation of hydroxide species that exhibit reduced affinity for binding to the functional groups of humic acids. At a pH of 1.7, hydrolytic reactions are minimal, thus favouring the retention of metal ions in their free ionic state [34,35,36].

3.3. The Application of a Sorption Material to Purify Surface Water Stream Flows at the ‘Degelen’ Site

Table 5. Comparison results and % of sorption with application of ICS-3A, µg/dm³ (average content, n = 4).

Elements	Tunnel 104			Tunnel 165			Tunnel 176			Tunnel 504			Tunnel 511
	pH = 7.8			pH = 8.0			pH = 7.7			pH = 5.6			pH = 6.8
	C1	C2	% of Sorption	C1	C2	% of Sorption	C1	C2	% of Sorption	C1	C2	% of Sorption	C1	C2	% of Sorption
Be	2.9 ± 0.3	0.32 ± 0.09	89	0.8 ± 0.1	0.17 ± 0.05	78	0.7 ± 0.1	0.10 ± 0.03	86	250 ± 2	250 ± 2	-	81 ± 1	3.8 ± 0.3	95
Al	30 ± 3	4600 ± 28	−96	27 ± 4	4200 ± 37	−99	69 ± 4	6900 ± 47	−99	-	-		778 ± 13	5600 ± 72	−86
Zn	5 ± 1	120 ± 2	−96	65 ± 1	195 ± 2	−67	41 ± 1	194 ± 3	−79	8300 ± 300	1700 ± 19	79	3160 ± 44	210 ± 4	93
Sr	500 ± 9	54 ± 1	89	310 ± 5	51 ± 1	83	176 ± 2	40 ± 1	77	422 ± 18	110 ± 3	74	340 ± 7	59 ± 1	83
Mo	1180 ± 26	58 ± 1	95	70 ± 1	70 ± 1	-	220 ± 2	80 ± 1	64	<0.01	25 ± 1	-	1.4 ± 0.1	59 ± 2	−98
Cd	1.1 ± 0.1	0.14 ± 0.05	88	<0.01	0.20 ± 0.08	-	0.5 ± 0.1	0.17 ± 0.03	62	19 ± 1	0.30 ± 0.03	98	9.2 ± 0.5	0.20 ± 0.07	98
Cs	2.3 ± 0.1	0.15 ± 0.01	93	1.25 ± 0.02	0.13 ± 0.01	89	0.68 ± 0.03	0.11 ± 0.01	83	3.7 ± 0.1	0.75 ± 0.03	80	3.5 ± 0.2	0.20 ± 0.01	95
Pb	<0.01	1.5 ± 0.02	-	<0.01	7.5 ± 0.2	-	<0.01	11 ± 1	-	13 ± 1	6.7 ± 0.1	47	1.8 ± 0.1	7.3 ± 0.3	−75
U	1300 ± 28	200 ± 3	84	585 ± 8	180 ± 2	69	350 ± 6	173 ± 2	51	202 ± 8	157 ± 3	23	200 ± 4	200 ± 4	-

Note: C₁—the average content of elements in the actual water samples; C₂—the average content of elements in the water following the experiment.

presents the results of using the ICS-3A agent with samples from the surface waters of the elected tunnels at the ’Degelen’ site in the laboratory study. For the analysis, we selected elements interacting with the agent. It was previously noted that the selection of elements was based on their increased concentration and the difference between the initial and equilibrium concentrations in the solutions.

As is seen from the table, ICS-3A sorbs such elements as Be, Sr, Mo, Cd, Cs, and U well. The sorption percentages for this agent are as follows: Be, 78–95%; Sr, 74–89%; Mo, 64–95%; Cd, 62–98%; Cs, 80–95%; and U, 23–84%. This agent showed high sorption capacity in the water of tunnel 504, which is notable for a slightly acidic pH. Along with heavy metals, the agent’s high efficiency is noted with respect to the group of rare earth elements. Sorption indicators for Cd²⁺ ions proved to be higher at pH < 7, which is probably related to features of the ion-molecular state of Cd in solutions.

4. Discussion

The Application of a Sorption Material to Purify Surface Water Stream Flows at the ‘Degelen’ Site

At the initial stage, we obtained data on the sorption capacity of the Bekturov Institute’s sorbent. This agent has demonstrated good efficiency in the purification of liquids from various metals and radioactive elements. Studies on the sorption of metal ions were conducted under controlled laboratory conditions [37].

Along with the static sorption technique proposed in [37], we used a more simplified dynamic analysis technique. The findings obtained under static conditions demonstrate that the sorbent has low efficiency (below 30%) and that this technique is unfeasible in situ. Consequently, the dynamic analysis technique proved to be more promising not only in terms of TM and TE sorption but also in its applicability to environmental compartments.

The obtained data on the application of the sorbent to surface watercourses allow for the determination of the maximum sorption capacity of this preparation for HM ions. For example, in [27], the maximum sorption capacity of the humic substance from black alder lowland peat for lead and zinc ions was determined to be 39 ± 3 and 32 ± 2 mg/g, respectively. In our experiments with natural water bodies, this value for lead ions was 0.32 mg/g, while for zinc ions, it was significantly higher at 330 mg/g (tunnel 504; pH 5.6). Notably, due to ions such as Sr, U, and Mo (tunnel 104; pH 7.8), the preparation had high sorption capacity values of 22 mg/g, 55 mg/g, and 56 mg/g, respectively.

The sorption capacity of ICS-3A, using Zn as an example, is 330 mg/g, which is advantageous in comparison with such known sorbents as activated carbon. The sorption capacity of powdered activated carbon AU (PAC) is 13 mg/g Zn, and that of carbon nanotubes (SWCNT and MWCNT) reached ~43–44 mg/g. According to the research undertaken by I.A. Kuznetsova [38], humic acids in the alkaline solution have a higher sorption capacity compared to those in the acidic solution due to their transition from a colloidal state to a truly soluble one; as a result, the functional groups of humic acids have a greater capacity for the ion exchange process. Accordingly, when the mass fraction of soluble HA in the system increases, so does the sorption level. As reported in [33], the best extraction of HM ions by humic acids in the studied range occurs at pH = 7.

The experimental results of our study on tunnel water samples confirm that alkaline solutions with pH ≥ 7 exhibit the best sorbing efficiency, which is attributed to agent solubility in the alkaline medium and, accordingly, to the functional groups of humic acids having an enhanced ability to undergo the ion exchange process.

The data obtained on U confirms earlier research [39] showing that the sorption efficiency of this HA element depends on water pH. For example, at pH ≤ 6, U sorption in test water samples by the ICS-3A agent is well below 23%. This is attributed to the generation of positive charges arising from amino groups on the surfaces of HA, which improve H+ competition for U at binding sites, leading to reduced U adsorption.

The concentrations of Al, Zn, Pb, and REE in the resulting water filtrate following the application of this agent proved to be well above those in the original sample. Such elevated contents of elements in the filtrate that resulted from the experiment are attributable to the elemental composition of the agent itself (Table 1). It should also be noted that the desorption of specified elements occurs at pH < 7. Additionally, unlike other HM ions and TEs, for Pb²⁺ ions in the acidic medium, the sorption capacity of HA ions barely depends on pH [40].

5. Conclusions

“Superhumate” demonstrates a high sorbing efficiency at the level of 60–95% when applied under dynamic conditions with a natural pH of 6.5; for REEs, this index reaches 98%. The agent’s higher sorption capacity should be noted with respect to such TMs as Sr, Mo, U, and Zn.

Estimated results regarding the dynamics of variations in organically bound carbon in the water point to the interrelation between water pH and agent solubility. The findings obtained based on simulated solutions at pH = 1.7 show that the agent does not sorb Cd, Cu, Pb, and Zn. The agent’s throughput in vitro directly depends on the diameter of the chromatographic column (sorbent location).

In summary, this sorbent can be used in sorbing TEs and TMs to remediate STS lands for the benefit of the national economy. Sorption of metals by ICS-3A under field conditions can be carried out in columns with liquid flow or filters. A column with a certain diameter and height can be loaded with a sorbent of a given mass through which contaminated water will pass. The sorbent demonstrates high sorption capacity with respect to TEs and TMs from surface water streams of tunnels at the Degelen site of the STS. It should also be noted that the ICS-3A agent is of natural origin and not environmentally toxic.