Effect of Water Treatment on the Chemical Composition of Drinking Water: A Case of Lovozero, Murmansk Region, Russia

Abstract

The surface waters in Russia’s Murmansk Region used for public water supply are exposed to the negative impact of dust particles carried from the storage facilities for mining waste. For example, lanthanides and other rare metals enter the surface waters in Lovozero District from the tailings storage facilities (TSFs) of the Lovozero Concentrator, which requires thorough water treatment of drinking water. Using the monitoring data of the natural water of the Virma River and of the tap water in the residential community of Lovozero, Murmansk Region, and with the help of physical and chemical modeling (in the software suite Selector), we examined the effect of reagents used in water treatment on water chemistry. It was shown that the use of aluminum polyoxydichloride coagulant can lead to an increase in the concentration of aluminum and chlorine in water, a change in pH and Eh values. The use of liquid chlorine leads to a decrease in pH values and a change in the concentration of HCO₃⁻, which entails a change in the forms of migration of calcium and lanthanides in solution. The composition of the precipitated phases changed, which indicates a change in the water chemistry, demonstrating that the applied water treatment technology adopted in Lovozero fails to improve water quality. It was shown that replacing liquid chlorine (a hazardous reagent) with NaOCl optimized the water treatment process, eliminating the need to stabilize the pH by adding sodium. Physical and chemical modeling was found to be useful for studying and optimizing water treatment processes.

1. Introduction

Waste water and drinking water treatment is an important and relevant environmental problem faced by the industry [1]. Our review of the existing research on water treatment and processing demonstrated that it is crucial to apply water treatment and disposal methods or develop a treatment process for each water body, taking into account its physical and chemical properties and ionic composition [1,2]. Treatment methods are conventionally classified into mechanical such as filtration and chemical–when the process line includes mechanical settling under the action of coagulants, chlorination, filtration, and pH control [1,3].

The principle of coagulant action is as follows: a reagent is introduced into the water contaminated with fine colloidal particles that pass through the filter; particle properties begin to change; they lose their charge, which enabled them to repel each other in a liquid under the action of electrostatic interaction forces; the suspension begins to coagulate, forming larger particles; attraction forces are activated. It is believed that reagents do not change water chemistry. They are needed in order to make the particles large for deposition on the filter. As a rule, aluminum and iron salts capable of neutralizing the charge are used as coagulants [3]. Most often, these agents are used to treat drinking water, industrial and domestic wastewater, water at aquaparks and swimming pools. Water intended for further consumption undergoes, both before and after treatment with coagulants, advanced chemical analysis to accurately calculate the dosage [3,4].The lack of chemical analysis calls into question the invariance of water chemistry [5,6].

In water treatment, electrochemical methods are currently being increasingly used [7]. Yakutniiproalmaz and URAN IPKON RAS proposed a method for processing circulating chloride-containing waters into hypochlorite solutions by electrolysis, when under the action of an electric current on the anodes, chloride ions are oxidized to ClO⁻, ClO₃⁻ ions and free chlorine. The latter in the liquid phase undergoes the reaction Cl₂ + H₂O = HCl + HClO (2H⁺ + Cl⁻ + ClO⁻), as a result of which the circulating water transforms into a solution with the required concentration of active chlorine [2].

In this study, using the monitoring data of the natural water in the Virma River and the tap water in Lovozero, Murmansk Region, the effect of reagents used in water treatment was investigated.

According to its chemistry, the water from the water intake (the Virma water) is characterized by a high natural content of iron, color index, and turbidity. According to the water chemistry tests carried out by Olenegorskvodokanal and the Murmansk Region Center for Public Health and Epidemiology in Monchegorsk, Olenegorsk, and Lovozero Districts on the samples from the water intake and water supply system in Lovozero, the following conclusion was made: water from the Virma River does not meet the Quality Guidelines for Drinking Water [8]. At present, the wear of the public water supply systems is 93%.

The water treatment process adopted for the central water supply system in Lovozero includes filtration, coagulation, and chlorination [9]. Disinfection is done with liquid chlorine supplied by JSC Kaustik, Volgograd, in accordance with the GOST (state standards) and with aluminum polyoxychloride (coagulant) of the AQUA-AURAT brand, the pH of the water is stabilized with a solution of soda ash with a concentration of 50 mg/L.

The work is devoted to the study of water treatment technologies carried out in Russia. Analysis of the cited literature allows to conclude that none of the mentioned researchers conducted such a complete chemical analysis on water, being limited to 10–20 components and pH values (e.g., Cu, Ni, Fe, NO₃⁻, NH₄⁺, etc.). The authors made the first attempt to study the effects of reagents used in water treatment, with the determination of the full hydrochemical composition of natural and drinking water by modern methods of research and physico-chemical modeling, among others. The cited researchers solved a specific narrowly focused problem [1] authors in this work developed a general approach to water treatment.

The goal of this study was to assess the change in the chemical composition of drinking water in Lovozero, Murmansk Region, as a result of water treatment using physical and chemical modeling in the software suite Selector. At one of the stages of the study, we considered the effect of free chlorine on the chemical composition of river water, and this approach may be applicable to wastewater treatment.

2. Materials and Methods

In this study, we used chemical analysis data on water samples. Surface and ground water monitoring included complete determination of the water’s hydrochemical composition using precision methods of analysis, such as inductively coupled plasma mass spectrometry (ELAN 9000 DRC-e, PerkinElmer, Waltham, MA, USA), potentiometry (Liquid Analyzer Expert-001, Ekoniks-Expert, Moscow, Russia), and titrimetry. Fluorine concentrations were estimated thermodynamically [10] and are comparable with earlier studies of natural water samples from the Khibiny Massif [11].

All thermodynamic calculations were performed using the method of physicochemical (thermodynamic) modeling implemented in the software suite Selector developed under the guidance of Professor I.K. Karpov at the Vinogradov Institute of Geochemistry, (SB RAS, Irkutsk, Russia). Selector has built-in databases of thermodynamic data, features a module for building models of varying complexity. The algorithm used [12] makes it possible to calculate complex chemical equilibria under isobaric-isothermal, isochemical and adiabatic conditions in multisystems, where an aqueous electrolyte solution, a gas mixture, liquid and solid hydrocarbons, minerals in the form of solid solutions and single-component phases, melts and plasma can co-exist. With the help of the software, it is possible to study both multicomponent heterogeneous systems and megasystems consisting of interacting systems (reservoirs) connected to each other and the environment by flows of matter and energy.

Physico-chemical model included 42 independent components (Al, B, Br, Ar, He, Ne, C, Ca, Cl, F, Fe, K, Mg, Mn, N, Na, P, S, Si, Sr, Cu, Zn, Ni, Pb, V, Ba, U, Ag, Au, Co, Cr, Hg, As, Cd, Mo, Se, La, Ce, Zr, H, O, ē), 1062 dependent components, of which 435 in an aqueous solution, 76 in the gas phase, 111 liquid hydrocarbons, 440 solid phases, organic and mineral substances. The set of solid phases of the multisystem was selected taking into account the mineral composition of the Baltic Shield rocks [13,14]. Initial thermodynamic information is given in [15,16,17,18,19,20].

Stability and accuracy of the system in the uncertainty regime are presented in [10].

In this study, the Selector software was also used for modeling in the water-reagent system.

3. Results and Discussion

Objects of research. Figure 1 shows the Lovozero Tundra Mountains and water sampling locations in November 2021. As part of the fieldwork, we collected water samples from the Virma River and the central water supply system (in the diner and tap water).

For this study, we used a physicochemical model of water–rock interactions, adapted to the conditions of Murmansk Region and allowing to assess the environmental situation in the presence of natural or anthropogenic impacts [14].

Table 1. Analysis data (AD) and modeling results (MR) of natural and drinking water (November 2021, T 20 °C), mg/L.

Indicator	Virma River		Tap Water-Lovozero		Indicator	Virma River		Tap Water
	AD	MR	AD	MR		AD	MR	AD	MR
Eh		0.828		0.770	Ba	0.0047	4.71 × 10−3	0.0028	2.83 × 10−3
pH	6.67	6.667	7.68	7.688	Ba2+		4.71 × 10−3		2.83 × 10−3
Is (ionic strength)		0.000575		0.001381	BaCO3		1.53 × 10−7		2.38 × 10−6
Al	0.057	5.71 × 10−2	0.176	1.76 × 10−1	BaCl+		1.00 × 10−7		3.05 × 10−7
Al(OH)2+		1.17 × 10−3		1.17 × 10−4	BaOH+		4.25 × 10−10		2.56 × 10−9
Al(OH)2F		9.16 × 10−2		5.37 × 10−3	Si	6.31	6.31	5.46	5.46
Al(OH)2F2−		2.03 × 10−4		7.18 × 10−6	SiO2		4.48		3.86
AlO2−		1.77 × 10−2		1.94 × 10−1	HSiO3−		6.29 × 10−3		5.77 × 10−2
HAlO2		1.40 × 10−2		1.43 × 10−2	H4SiO4		14.4		12.4
Al(OH)2+		2.74 × 10−4		2.73 × 10−6	Sr	0.0333	3.32 × 10−2	0.0328	3.28 × 10−2
Al(OH)3		1.22 × 10−2		1.24 × 10−2	Sr2+		3.31 × 10−2		3.24 × 10−2
Al(OH)4−		2.42 × 10−2		2.65 × 10−1	SrOH+		5.19 × 10−9		5.08 × 10−8
Al3+		4.63 × 10−6		4.73 × 10−9	SrCO3		2.07 × 10−6		5.25 × 10−5
Ca	3.06	3.06	3.96	3.96	SrHCO3+		2.45 × 10−4		6.01 × 10−4
Ca2+		3.04		3.91	SrCl+		1.45 × 10−6		7.19 × 10−6
CaOH+		1.74 × 10−6		2.23 × 10−5	SrF+		6.87 × 10−7		3.83 × 10−7
CaCO3		8.33 × 10−4		2.77 × 10−2	Zn	<0.00001		<0.00001
Ca(HCO3)+		2.50 × 10−2		8.05 × 10−2	Cd	0.00003	2.80 × 10−5	0.00003	2.88 × 10−5
CaHSiO3+		7.22 × 10−6		7.99 × 10−5	Cd2+		2.78 × 10−5		2.79 × 10−5
CaCl+		1.62 × 10−4		1.06 × 10−3	CdCl+		2.07 × 10−7		1.05 × 10−6
CaCl2		6.80 × 10−9		2.33 × 10−7	CdO		1.45 × 10−12		1.50 × 10−10
CaF+		2.65 × 10−4		1.94 × 10−4	CdOH+		8.58 × 10−9		8.60 × 10−8
CaSO4		2.58 × 10−2		3.15 × 10−2	Ni	<0.00001		<0.00001
B	0.0095	9.50 × 10−3	0.00803	8.03 × 10−3	Pb	0.00006	6.35 × 10−5	0.00007	7.93 × 10−5
H3BO3		5.42 × 10−2		4.48 × 10−2	Pb2+		1.57 × 10−5		2.51 × 10−6
BO2−		8.74 × 10−5		7.69 × 10−4	PbOH+		5.17 × 10−5		8.30 × 10−5
Fe	0.76	7.60 × 10−1	0.292	2.92 × 10−1	PbO		2.36 × 10−9		3.91 × 10−8
Fe2+		7.29 × 10−10		3.92 × 10−12	PbCl+		2.83 × 10−8		2.31 × 10−8
FeSO4+		5.15 × 10−9		2.79 × 10−12	Cu	0.0003	2.86 × 10−4	0.0012	1.19 × 10−3
Fe(OH)3		7.03 × 10−2		4.16 × 10−2	Cu+		6.73 × 10−16		1.95 × 10−14
Fe(OH)4−		1.77 × 10−3		1.11 × 10−2	Cu2+		2.75 × 10−4		8.45 × 10−4
FeOH2+		3.15 × 10−4		1.80 × 10−6	CuCl+		6.19 × 10−8		9.70 × 10−7
FeOH+		1.51 × 10−12		8.11 × 10−14	CuOH+		1.40 × 10−5		4.33 × 10−4
FeO+		3.94 × 10−1		2.25 × 10−2	CuF+		1.50 × 10−7		2.65 × 10−7
FeSO4		3.32 × 10−12		1.69 × 10−14	CuCl2−		-		1.09 × 10−15
HFeO2		6.61 × 10−1		3.91 × 10−1	HCuO2−		4.30 × 10−12		1.46 × 10−8
FeO2−		5.77 × 10−4		3.63 × 10−3	P		3.26 × 10−4		3.26 × 10−4
FeCl+		4.69 × 10−14		1.28 × 10−15	PO43−	0.001	4.51 × 10−10	0.001	1.75 × 10−8
FeF+		3.31 × 10−13		1.01 × 10−15	HPO42−		2.23 × 10−4		7.65 × 10−4
FeF2+		1.64 × 10−7		5.38 × 10−11	H2PO4−		7.96 × 10−4		2.48 × 10−4
F−		2.46 × 10−1		1.88 × 10−1	Co	0.00007		0.00009	8.67 × 10−5
HF		7.45 × 10−5		5.60 × 10−6	Co2+		9.72 × 10−5		8.64 × 10−5
HF2−		4.33 × 10−10		2.48 × 10−11	CoO		2.01 × 10−10		1.85 × 10−8
K	0.41	4.10 × 10−1	0.630	6.30 × 10−1	CoCl+		3.38 × 10−8		1.53 × 10−7
K+		1.16 × 10−7		6.30 × 10−1	HCoO2−		1.86 × 10−16		1.82 × 10−13
KCl		1.16 × 10−7		9.34 × 10−7	CoOH+		3.80 × 10−8		3.38 × 10−7
KHSO4		6.48 × 10−9		2.20 × 10−14	Cl	2.09		11.3	11.3
KOH		2.15 × 10−4		1.03 × 10−7	Cl−		2.09		11.3
KSO4−		4.10 × 10−1		3.34 × 10−4	HCl		9.59 × 10−8		4.87 × 10−8
Mg	1.57	1.57	1.92	1.92	Zr	0.0008	7.98 × 10−4	0.00029	2.95 × 10−4
Mg2+		1.56		1.90	HZrO3−		8.13 × 10−4		4.32 × 10−4
MgOH+		1.66 × 10−5		2.02 × 10−4	ZrO2		3.63 × 10−4		1.81 × 10−5
MgCO3		2.79 × 10−4		8.78 × 10−3	U	0.00005	4.55 × 10−5	0.00003	2.87 × 10−5
Mg(HCO3)+		1.73 × 10−2		5.28 × 10−2	HUO4−		2.68 × 10−7		1.77 × 10−6
MgCl+		1.62 × 10−4		1.00 × 10−3	UO22+		6.76 × 10−8		4.06 × 10−10
MgF+		7.88 × 10−4		5.46 × 10−4	UO2OH+		1.50 × 10−6		9.04 × 10−8
MgSO4		2.53 × 10−2		2.92 × 10−2	UO2		-		-
MgHSiO3+		9.67 × 10−6		1.01 × 10−4	UO3		5.29 × 10−5		3.28 × 10−5
Mn	0.0467	4.67 × 10−2	0.0161	1.61 × 10−2	Li	0.00025	2.53 × 10−4	0.00037
Mn2+		4.66 × 10−2		1.61 × 10−2	Li+		2.53 × 10−4		3.68 × 10−4
MnOH+		4.51 × 10−6		1.56 × 10−5	LiOH		6.23 × 10−11		9.38 × 10−10
MnO		3.50 × 10−11		1.25 × 10−9	Ce	0.00023	2.26 × 10−4	0.00005	4.67 × 10−5
HMnO2−		-		1.46 × 10−14	Ce3+		1.75 × 10−4		3.54 × 10−5
MnSO4		1.97 × 10−4		6.45 × 10−5	CeF2+		3.58 × 10−5		4.03 × 10−6
MnF+		5.98 × 10−6		1.18 × 10−6	CeF2+		6.06 × 10−7		3.89 × 10−8
MnCl+		2.85 × 10−6		4.99 × 10−6	CeF3		1.74 × 10−9		6.58 × 10−11
CO32−		3.56 × 10−3		1.04 × 10−1	CeF4−		2.43 × 10−12		5.57 × 10−14
HCO3−	15.7	18.2	49.12		CeHCO32+		5.74 × 10−6		2.83 × 10−6
HCO3−				4.87 × 10−1	CeO2H		3.11 × 10−11		6.33 × 10−9
HCO2−				-	CeSO4+		2.24 × 10−5		4.07 × 10−6
SO42−	2.03	1.99	2.19	2.14	CeOH2+		1.91 × 10−6		3.77 × 10−6
HNO3		5.55 × 10−12		5.49 × 10−11	La	0.00015	1.54 × 10−4	0.00006
NO3−	0.001	7.71 × 10−4	0.08	8.14 × 10−2	La3+		7.65 × 10−5		2.77 × 10−6
Na+	2.62	2.62	18.64	18.6	LaCO3+		9.06 × 10−5		7.99 × 10−5
NaOH		9.06 × 10−8		6.65 × 10−6	LaF2+		6.60 × 10−6		1.32 × 10−7
NaAlO2		4.72 × 10−7		3.55 × 10−5	LaO+				1.44 × 10−9
NaCl		6.30 × 10−5		2.35 × 10−3	LaO2H		2.25 × 10−13		8.17 × 10−12
NaF		5.89 × 10−6		2.46 × 10−5	LaOH2+		5.05 × 10−7		1.78 × 10−7
NaSO4−		1.35 × 10−3		9.65 × 10−3	LaSO4+		9.89 × 10−6		3.20 × 10−7
NaHSiO3		7.28 × 10−5		4.60 × 10−3	LaF2+		6.68 × 10−8
O2		6.10		7.74	Ag	0.0013	1.34 × 10−3	0.0014
CO2		6.61		1.66	Ag+		5.54 × 10−8		1.43 × 10−9
V	0.0007	7.37 × 10−4	0.0007	7.39 × 10−4	AgNO3		6.29 × 10−4		1.66 × 10−3
VO2+		2.40 × 10−8			Ag(HS)2−		-		-
VO43−		3.39 × 10−10		8.46 × 10−13
HVO42−		1.61 × 10−3		1.68 × 10−3
H3VO4		6.68 × 10−5		6.55 × 10−7

presents the analysis data and the modeling results of the water samples from the Virma River and the tap water samples.

Our analysis of the results (Table 1) indicated that after water treatment, the concentration of Al, Na and HCO₃⁻ increased.

Using physicochemical modeling, various scenarios of water-reagent interaction during water treatment (reagent composed of a 10% solution of aluminum polyoxychloride, liquid chlorine, and a 5% soda solution) were examined without precipitation of solid phases (metastable state) and with precipitation of solid phases (equilibrium state). Aluminum polyoxychloride is the reagent of choice (compared to other reagents) for the treatment of cold water high in natural organic impurities [4]. The chemical formula of the reagent used was Al(OH)_ACl_B∙nH₂O, where A + B = 3, with A ≥ 1.3. In our calculations, we adopted A = 1.3; B = 1.7.

Figure 2 shows the water treatment process used, and

Table 2. Chemical composition of a 10% solution of aluminum polyoxychloride Al(OH)_1.3Cl_1.7, T = 5 °C.

Concentration, mg/L
Al(OH)2+	AlO2−	HAlO2	Al(OH)2+	Al(OH)3	Al(OH)4−	Al3+	Cl−	Eh, V	pH
5.22 × 103 5.22 × 10³	9.64 × 102 9.64 × 102	8.30 × 103 8.30 × 10³	1.42 × 104 1.42 × 104	3.96 × 103 3.96 × 10³	4.50 × 103 4.50 × 10³	9.47 × 103 9.47 × 10³	6.10× 104 6.10 × 104	−0.216	6.07

shows the composition of a 10% solution of aluminum polyoxychloride at a temperature of 5 °C.

Analysis of the results (Table 2) showed that the slightly acidic reducing environment had a high concentration of Cl⁻ and aluminum compounds were dominated by Al(OH)²⁺. In the 1980–1990s, the toxicity of aluminum to the aquatic environment and humans was demonstrated in the literature. It is noteworthy that, as for most metals, the degree of toxicity depends on the form of aluminum in water. It was found that the greatest source of toxicity is the so-called inorganic monomer aluminum. Its most toxic forms include free (hydrated) ions or aqua complexes [Al(H₂O)₆]³⁺ and hydroxo-complexes Al(OH)₂⁺ and Al(OH)²⁺, found in a slightly acidic environment at pH 4.5–5.5 [21]. According to [22], the identified forms of Al(OH)₂⁺, Al³⁺ migrationare the most toxic for plants.

The interaction of a 10% solution of polyoxychloride with 1000 L of water from the Virma River at a temperature of 5 °C is shown in Figure 3, while

Table 3. Change in aluminum migration forms and concentration of HCO₃⁻ during the interaction of a 10% solution of polyoxychloride with 1000 L of water from the Virma River, mg/L (T = 5 °C).

10% Solution, L	Al(OH)2F	HAlO2	Al(OH)2+	Al(OH)2+	Al(OH)3	AlSO4+	Al3+	HCO3−
0.0001	4.73 × 10−5	4.55 × 10−6	4.70 × 10−7	2.13 × 10−6	3.26 × 10−6	5.47 × 10−11	1.85 × 10−8	17.7
0.0032	5.01 × 10−5	4.57 × 10−6	5.25 × 10−7	2.26 × 10−6	3.28 × 10−6	6.45 × 10−11	2.18 × 10−8	17.4
0.0100	5.75 × 10−5	4.67 × 10−6	6.77 × 10−7	2.59 × 10−6	3.35 × 10−6	9.35 × 10−11	3.16 × 10−8	16.6
0.0316	8.65 × 10−5	4.92 × 10−6	1.46 × 10−6	3.90 × 10−6	3.53 × 10−6	2.87 × 10−10	9.70 × 10−8	14.2
0.1000	3.96 × 10−4	6.55 × 10−6	2.38 × 10−5	1.81 × 10−5	4.70 × 10−6	1.56 × 10−8	5.67 × 10−6	6.42
0.3162	6.42 × 10−2	3.02 × 10−5	1.82 × 10−1	3.34 × 10−3	2.17 × 10−5	4.17 × 10−3	1.86	0.213
1.0000	9.94 × 10−2	3.02 × 10−5	5.93 × 10−1	5.84 × 10−3	2.17 × 10−5	1.84 × 10−2	12.0	0.130

shows the change in the forms of aluminum migration and their concentrations.

Our analysis of the presented results (Figure 3 and Table 3) indicated that when more than 0.01 L of coagulant is added to the system, the values of pH and Eh (Figure 3b) and the composition of the newly formed phases (Figure 3c) change, and the concentrations of Al and Cl increase (Figure 3a). As mentioned above, the toxic forms of aluminum begin to predominate. Changing the concentration of HCO₃⁻ leads to a decrease in carbonates and bicarbonates of calcium and magnesium. An increase in the concentration of chlorine (Figure 3a) leads to an increase in the concentration of sodium and calcium chlorides. There is a change in the forms of migration of lanthanides and uranium.

Our findings at this stage indicate the danger associated with excessive amounts of the coagulant, and adding coagulant at 0.01 L per 1000 L of water is considered to have the least impact on the chemical composition of water (Table 3).

Disinfection of household and drinking water in Lovozero is achieved at a chlorination plant with liquid chlorine that meets the requirements of the GOST- state standards (JSC Kaustik, Volgograd, Russia) [9]. Therefore, the next stage of the study was to examine the interactions between river water and liquid chlorine. 1000 L of river water and liquid chlorine (Cl₂) were adopted as the boundary conditions of the model. The simulation results are shown in Figure 4. The results indicate a shift in pH to acidic values (Figure 4a) and an increase in the concentration of chlorine in the aqueous environment (Figure 4b). A change in the concentration of HCO₃⁻ entails a change in the concentration of carbonates and bicarbonates Ca and Mg. Figure 4c,d shows the forms of element migration using the example of calcium and lanthanum: an increase in the concentration of CaCl⁺, a decrease in the concentrations of CaCO₃, CaHCO₃⁺, La³⁺ starts to dominate, replacing LaCO₃⁺.

The forms of aluminum migration also changed. Al(OH)₂F prevailed in natural water (0.138 mg/L subsequently, as the concentration of chlorine increased to 0.3981 mol and pH 3.34, the concentration of Al(OH)₂F decreased to 8.52E-06 8.52 × 10⁻⁶ mg/L, and Al³⁺ increased to 5.68 × 10⁻² mg/L, i.e., Al³⁺ became the predominant form of aluminum migration. It is this value of chlorine and the composition of chlorine water that were adopted to study the system river water—0.01 L of 10% Al(OH)_1.3Cl_1.7—chlorine water (Cl₂ 0.3981 mol).

The results of mixing 1000 L of river water with the addition of 0.01 L of a 10% solution of the coagulant Al(OH)_1.3Cl_1.7 and 1 to 10,000 L chlorine water are shown in Figure 5.

As the results show, when mixing more than 100 L of chlorine water with river water and reaching a chlorine concentration of more than 5 mg/L, a sharp change in pH, a decrease in the concentration of HCO₃⁻, and a change in the forms of migration of all microelements are observed. Adding more than 1000 L of chlorine water to the system leads to the transition of a number of elements into solution (for example, Mn), and SiO₂ becomes the predominant newly formed phase (Figure 5c). The state of the system when mixing 1000 L of river water with chlorine water (

Table 4. Changes in the parameters of chlorinated river water after adding a 5% soda solution.

5% Solution Na2CO3, L	Eh	pH	Na+, mg/L	Cl−, mg/L	HCO3−, mg/L
0	0.997	4.03	2.62	16.5	9.23 × 10−2
1	0.857	6.58	14.0	16.5	23.1
2	0.804	7.54	25.3	16.5	53.0

) was preserved by adding soda to stabilize the pH.

Table 4 shows the changes in the parameters of chlorinated river water after adding a 5% soda solution.

Physicochemical modeling makes it possible to predict changes in the forms of migration of both macro- and microcomponents of water and, if necessary, optimize the flow rate of reagents, or suggest another type of reagents. Instead of chlorinating river water with liquid chlorine and then neutralizing it with a soda solution, it was proposed to use a sodium hypochlorite solution.

Modeling results for 1000 L of the Virma River water treated with Al(OH)_1.3Cl_1.7–NaOCl are presented in Figure 6.

Analysis of the obtained results leads to the conclusion that NaOCl does not lead to a change in pH, Eh, HCO₃⁻, the migration forms of macro- and microcomponents do not change, oxygen is released, and an increase in its concentration leads to oxidation and precipitation of solid phases. At a NaOCl concentration of 0.31623 mol in the system, the concentrations are Cl⁻ 13.9 mg/L, Na 9.85 mg/L, HCO₃⁻ 16.6 mg/L, pH 6.68, which matches the values observed in a natural environment. There is no need to add soda to regulate pH when adding NaOCl salt, there is no need to chlorinate, which simplifies the water treatment process, but does not bring the water chemistry closer to bottled water and does not make it more valuable in terms of its macrocomponent composition (

Table 5. Comparison of concentrations of elements before and after water treatment in various quality grades of water, mg/L.

Element	Natural Water (Virma)	Drinking Water (Diner)	Adequacy [23]	Maximum Allowable Concentrations, SanPIN2.1.4.1116-02 [24]
				Grade 1	Top Grade
Na	1.88	19.87	2–20	200	20
Mg	1.28	1.31	5–65	65	5–50
Al	0.057	0.29	-	0.2	0.1
Si	5.45	5.31	-	1.02	4.83
P	0.018	0.001	-	-	-
K	0.31	0.49	2–20	20	2–20
Ca	1.54	3.07	25–130	130	25–80

).

4. Conclusions

Physicochemical modeling and field data (monitoring data) made it possible to reconstruct the water treatment process and evaluate the effect of each reagent on the water chemistry.

The use of liquid chlorine leads to a decrease in pH, a change in the concentration of HCO₃⁻, which entails a change in the forms of migration of aluminum and lanthanum in solution. The composition of the precipitated phases changes, which indicates a change in the chemical composition and structure of water.

The applied water treatment process (in Lovozero) failed to bring the water chemistry closer to bottled water and did not make it more valuable in terms of macrocomponent composition.

Our modeling showed that replacing liquid chlorine (a hazardous substance) with NaOCl salt optimized the water treatment process, eliminating the need to stabilize the pH by adding soda.

The proposed approach makes it possible to significantly improve environmental and industrial safety and reduce operating costs when providing the mining region with industrial (including circulating) and drinking water.

The use of physicochemical modeling is a valid approach to studying and optimizing the processes of water treatment and concentration.

The approach applied by us (method of physical-chemical modeling) can act both as an independent study (when the experiment is impossible in principle), and as an auxiliary (additional) means for planning the laboratory (industrial) experiment. Thermodynamics shows the direction of the process, without taking into account the kinetic factor, which can only be evaluated by laboratory experiment or enlarged bench tests.

The study was carried out as part of the research areas 1021051803677-1, FMEZ-2022-0010, FMEZ-2022-0018.