Apatity scientists built a model of air pollution with dust from the tailings

(ORDO NEWS) — Researchers from the Kola Science Center have created a digital model of the tailings of an enrichment plant. It can be used to predict air pollution in a city located near this factory, depending on the area of ​​dusty areas and the strength of the wind.

Residents of cities located near processing plants that process minerals know the expression – “tails are dusty.” It means that in the warm and dry season, the smallest dust is suspended in the air of the city.

Somewhere the suburbs are suffering, somewhere the central regions are plunging into dust. Why does this problem exist and why was it not taken into account when building the factory? Is it really impossible to completely get rid of this dust?

The vast majority of ores throughout the world must be enriched , that is, cleaned from ballast substances that are unnecessary for further production. The waste products from this process are called tailings. Unfortunately, mining production does not exist without “tails” at all.

A tailing dump appears next to each factory – a site onto which an aqueous suspension of small particles of ballast substances is poured. As it dries, it turns to dust and rises into the air. The intensity of dusting depends on many factors. The chemical and physical properties of the “tails” are important.

For example, waste from the processing of loparite ores stick together into lumps and are less prone to dusting. Meteorological conditions are no less important: the drier and windier the weather, the more often and more intensively the “tails” dust.

And of course, the height and area of ​​the tailings are important. At a time when mining and processing plants and the cities serving them were just beginning to develop, tailings were still small and behaved much more “decently”. Alas, few people then assumed that with the growth of waste volumes, dusting increases not at all in a linear relationship.

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If we were to go back in time with our current experience, perhaps cities and factories were built differently, with smaller waste storage sites and more sheltered from the wind. But the past cannot be returned – you need to work with what has already happened.

Transforming tailings to reduce their dusting is a big and serious job. Research in this area is carried out by scientists from different scientific centers. But it is equally important to know what is happening with the “tails” now, and to predict the behavior and intensity of dust under different conditions.

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The city of Apatity is exposed every summer to the waste of apatite-nepheline production: a tailing dump with an area of ​​8.3 square kilometers, located to the north-west of the city at a distance of eight kilometers from it, is dusty. It is exposed to both the prevailing northwesterly winds and southerly winds.

In the 1980-1990s. of the last century, employees of the Kola Scientific Center of the Russian Academy of Sciences under the guidance of A. A. Baklanov (Baklanov, 1988; Baklanov, Rigina, 1998) made an attempt to numerically simulate the process of dust dispersion at the tailing dump closest to the city of Apatity.

In this case, the calculations were carried out according to the author’s models and computer programs, in which the equations describing the processes of aerothermodynamics were solved by finite-difference methods on non-uniform rectangular grids.

Since the work of the air flow on weighing the particles is small and they stay in suspension for a rather long time, their propagation was studied on the basis of the diffusion theory.

From the point of view of atmospheric pollution in the area of ​​the tailing dump at the initial stage of research (Baklanov, 1988), the interest was in dust particles with a size of 10-100 microns. However, at subsequent stages of research (Baklanov and Rigina, 1998), the size range of dust particles was extended from 5 to 200 µm.

Since the range of sizes of sheared and transported particles is quite wide, the authors of the works (Baklanov, 1988; Baklanov and Rigina, 1998) formalized and solved transport equations for several size intervals of dust particles in order to accurately take into account the settling rate.

In the 1980s-1990s, the staff of the Kola Science Center already made an attempt to simulate the process of dust dispersion at this tailing dump. However, the computing power at the disposal of scientists was not enough for a detailed assessment. In the early 2010s, these studies were resumed using new technologies and computer programs.

The result of many years of work was a digital model created by employees of the Institute of Industrial Ecology of the North of the Kola Scientific Center and the World Meteorological Organization, which makes it possible to predict local dust storms and atmospheric pollution.

The work was supported by the RFBR grant “Comprehensive assessment of the impact of microparticles in emissions from mining and metallurgical enterprises of the Murmansk region on ecosystems and the health status of the population of the Arctic”.

In different years and different months, different sections of the tailing dump are dusty, where specific conditions arise under certain meteorological parameters and technological operations.

It is these situations, taking into account the variation in the speed of the wind flow, the number of discrete sections selected randomly, and hence the area of ​​dusting, that the authors modeled.

The following parameters were used in numerical experiments: wind speed (5, 11, 17, and 23 m/s) at a height of 10 meters from the base of the model, dusting area (2, 4, 6, 8, and 10 ha), and average diameter of dust particles (35 µm).

With a more fractional gradation, the time for conducting research increases many times, and their accuracy in the terminology of the total concentration almost does not change.

The analysis of the model made it possible to identify the most polluted area of ​​the city. The authors also found that the dependence of dust concentration on the dusting area at a fixed wind speed is described with a high reliability coefficient by linear functions, and the dependence of dust concentration on the wind flow speed at fixed values ​​of the dusting area is described by a power law.

The authors obtained a generalized analytical expression that makes it possible to predict the dust concentration as a function of two parameters (dusting area and wind speed), and made a forecast of the critical dusting area at which the level of atmospheric pollution reaches the MPC with a variation in the wind flow speed.

For a more accurate understanding of the nature of dust pollution (the impact of dust with a diameter of less than 10 microns on plants and humans differs from medium-sized dust), scientists are going to conduct a full cycle of studies with interval distribution of dust by size.

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