Modeling the Process of Thawing of Tailings Dam Base Soils by Technological Waters

At a Glance

Metadata	Details
Publication Date	2021-11-23
Journal	Applied Sciences
Authors	Nataliya Yurkevich, Irina Fadeeva, E. P. Shevko, Alexey M. Yannikov, S. B. Bortnikova
Institutions	Institute of Petroleum Geology and Geophysics, V.S. Sobolev Institute of Geology and Mineralogy
Citations	2
Analysis	Full AI Review Included

Executive Summary

This study utilized combined thermophysical and thermodynamic modeling to assess the impact of warm industrial water leakage on permafrost base soils beneath a diamond mine tailings dam in a cold climate region (Yakutia).

Primary Threat Identified: Physical heating by circulating technological water is the dominant mechanism for permafrost degradation and filtration channel expansion, significantly outweighing exothermic chemical reactions.
Thermal Impact (Frozen Rock): Over a 10-year period, warm water transferred 207.8 GJ of heat to the frozen rock mass, leading to the formation of a thawing zone (talik) that expanded radially 1.5 m in the first year.
Thermal Impact (Thawed Rock): The water transferred 8.39 GJ of heat to the already thawed rock mass over 10 years, primarily maintaining the existing thawed state.
Chemical Impact: Thermodynamic modeling of limestone dissolution (estimated at 0.01% mass reacted) released 0.37 GJ of energy over 10 years.
Energy Contribution Ratio: The chemical heat release contributed only 4.4% of the energy received by the thawed rock mass from the circulating water, confirming that thermal management is the critical engineering priority.
Geochemical Outcome: Water-rock interaction promotes limestone dissolution, leading to Ca leaching and the formation of secondary minerals (e.g., gypsum, dolomite, illite), which can potentially decrease rock permeability and form natural seals.

Technical Specifications

Parameter	Value	Unit	Context
Simulation Period	10	years	Total modeling duration
Modeled Channel Diameter	15	cm	Simulated sub-vertical crack
Modeled Channel Length	66	m	Simulated sub-vertical crack
Water Inflow Velocity	100	m/day	Velocity of filtering industrial water
Water Inlet Temperature Range	0 to 15	°C	Annual fluctuation
Initial Frozen Rock Temp (T_i)	-4	°C	Well t3 (Frozen Zone)
Initial Thawed Rock Temp (T_i)	+4	°C	Well t1 (Thawed Zone)
Total Heat Transferred (Frozen Rock)	207.8	GJ	Cumulative heat transfer over 10 years
Average Channel Power (Frozen Rock)	659.01	W	Average power over 10 years
Average Specific Heat Flux (Frozen Rock)	21.26	W/m²	Average flux over 10 years
Total Heat Transferred (Thawed Rock)	8.39	GJ	Cumulative heat transfer over 10 years
Chemical Energy Release (Limestone)	0.37	GJ	Total energy from 0.01% dissolution over 10 years
Chemical Heat Contribution	4.4	%	Relative to heat received by thawed rock
Thawing Zone Radius (Year 1)	1.5	m	Radial distance of the -0.5 °C isotherm
Thermal Conductivity (Frozen Limestone)	2.91	W/m/K	Unit t3/2
Permeability (Porous Medium, k)	10^-12	m²	Assumed rock permeability
Water Dynamic Viscosity (µ)	10^-3	Pa·s	Assumed fluid property

Key Methodologies

The study employed a two-pronged modeling approach to simulate the complex thermal and chemical interactions within the tailings dam foundation.

Thermophysical Modeling (COMSOL Multiphysics):
- Flow Dynamics: Water velocity distribution in the crack and adjacent rock was calculated using the Navier-Stokes equations (free channel) and the Brinkman equation with Forchheimer correction (porous medium).
- Heat Transfer Simulation: The heat conduction equation, incorporating a convective term, was solved in temporary settings to model temperature changes over 10 years, accounting for seasonal fluctuations in water inlet temperature (0 °C to 15 °C).
- Thawing Rate Calculation: Determined the rate of permafrost thawing by tracking the movement of the 0 °C isotherm, calculating the total heat transferred, and deriving the average channel power and specific heat flux.
Thermodynamic Modeling (PC Selector Software):
- Equilibrium Calculation: Used minimization of the Gibbs free energy to determine the equilibrium composition of solutions and minerals resulting from water-rock interaction at 2 °C.
- Material Input: Modeled the interaction between industrial water (sulfate-chloride composition) and six rock types (limestone, marl, and tailings/psephites).
- Dissolution Estimation: The degree of rock transformation (estimated 0.01% limestone dissolution) was inferred by comparing bicarbonate ion changes in the settling pond and storage pond solutions.
- Exothermic Effect Quantification: Calculated the temperature rise (up to 4.2 °C) and the total energy released (0.37 GJ over 10 years) due to limestone dissolution and solution equilibration, quantifying the chemical contribution to heating.

Commercial Applications

This research provides critical data and modeling techniques essential for managing large-scale infrastructure and waste facilities in permafrost environments.

Tailings Storage Facility (TSF) Management: Direct application in designing and monitoring TSFs in cold climates to prevent permafrost degradation, which leads to structural instability and leakage.
Geotechnical Risk Mitigation: Provides engineers with predictive models to calculate the rate of filtration channel formation, allowing for timely intervention to prevent the leakage of mineralized or acidic drainage solutions.
Cold Climate Mine Reclamation: Supports the design of effective thermal covers and freeze encapsulation strategies by quantifying the heat load from circulating waters that must be counteracted to maintain frozen conditions.
Environmental Compliance and Monitoring: Offers a methodology to assess the long-term environmental impact of mining operations on surface and ground water quality in permafrost regions, particularly concerning the mobility of toxic elements.
Infrastructure Integrity in Arctic Regions: The modeling approach is transferable to other large infrastructure projects (e.g., pipelines, dams, foundations) where warm fluid circulation or heat generation interacts with frozen ground.

View Original Abstract

The storage of wastes from mining and mineral processing plants in the tailing dumps in regions with cold climates has a number of environmental consequences. Interactions of water with tailings in cold climates often lead to the thawing of permafrost soils, formation of technogenic thawing zones, and leakage of drainage waters. In the case of fault zones development in these areas, technogenic solutions are often filtered outside the tailing dump, promoting further development of filtration channels. In order to prevent leakage of solution from tailing dumps over time, it is necessary to determine the thawing zones and prevent the formation of filtration channels. In the case of the formation of a filtration channel, it is necessary to know what rate of rock thawing occurred near the formed filtration channel. In this study, for the tailing dump of a diamond mining factory, we calculated two exothermic effects: (1) due to physical heating of dump rock by filtering industrial water with temperatures from 2 to 15 °C through the rock; and (2) due to the chemical interaction of industrial water with the dam base rock. The amount of energy transferred by the water to the frozen and thawed rock over 10 years was calculated using thermophysical modeling and was 207.8 GJ and 8.39 GJ respectively. The amount of energy that the rock received during the ten-year period due to dissolution of the limestones and equilibration of solutions was calculated using thermodynamic modeling and was 0.37 GJ, which is 4.4% of the average amount of energy, expended on heating the thawed rock (8.39 GJ).

Tech Support

Original Source

DOI: https://doi.org/10.3390/app112311089

References

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