ENVIRONMENTAL IMPACT OF MINE WASTES APPLICATION TO EARTH CONSTRUCTIONS IN HYDRAULICS ENGINEERING

Jerzy Ratomski¹, Andrzej Zapał^2
1 Institute of Water Engineering and Management , Cracow University of Technology
² Institute of Geotechnics, Cracow University of Technology

ABSTRACT

This paper presents results of physical chemistry research on solutes leached from mine waste dumps. Radioactivity research of that solutes is also included, taking into consideration its usage in earth constructions of hydraulic engineering.

The research was done on samples taken from eight coal mine waste dumps.

Impact on the water environment of that solutes was assessed, together with their radioactivity effect. The conclusion of that research contains guidelines for usage of that mine wastes, concerning also its ecological as

Key words: Mine Wastes, Chemical pollution or radioactivity , Hydraulics Engineering.

INTRODUCTION

Mine deads are by-products of mining and coal processing. They are relatively rarely used and the effects of their storage on dumps are evidently detrimental. They are also area-consuming that can considerably mar the landscape. Fine, blown by winds or washed away fractions can pollute both soil and ground waters.

The problems of making use of mine wastes and availability of cheap materials for earth constructions have been widely covered in many papers and discussed by professionals in the literature on the environmental protection. Such sources can provide, at least partial, support in land reclamation of coal mine dumps, using mine wastes for building, particularly in earth constructions.

Large quantities of materials form stockpiles can be used properly provided that sufficient knowledge on mine wastes regarding both their geotechnical properties and impact on the environment has been acquired. Natural radioactivity of mine wastes and the pollutants (products of various chemical reactions) washed away with precipitation, surface and ground waters can result in environmental pollution. Chemical pollution or radioactivity in higher than permissible limits can also bring long-term adverse effects to the environment and threaten public health, thus eliminating the opportunity of using mine deads for such purposes.

The paper deals with presenting the results of psychical chemistry analysis of leachates as well as radioactivity analysis of colliery spoils from stockpiles with regard to their potential use for earth constructions.

AREA OF RESEARCH

Samples collected mainly at mine dumps of Vistula Mines Company, which includes selected mines of Upper Silesia Industrial Region, namely Ziemowit, Janina, Brzeszcze, Jaworzno, Jan Kanty, Bolesław Śmiały, Siersza and Silesia were analysed. Deads from these mines are of similar geological origin. They come from upper carboniferous sediments, syncline group, layers of Libiąż, Orzesze, Łaziska and Ruda. They are the youngest sediments, mostly argillaceous rocks, which can be described as weakly compacted, hardly resistant to weathering [5].

The mineralogical and petrografical composition of mine wastes is also similar since they are produced in a similar way and being by-products from floor and roof layers and coal interlayers, separated from coal during the process of washering. Hence, it seems reasonable to assume similarity of mine dumps samples from selected mines, and furthermore constitute the grounds for generalizing the conclusions of the research.

SCOPE AND METHODOLOGY OF RESEARCH

The following physical and chemical indexes were determined for the solute leached from mine wastes: reaction, specific electrolytic conductivity, alkalinity, sulphates, chlorides, ammonia nitrogen, nitrate nitrogen, iron, manganese, sodium, potassium, cadmium, chromium, copper, nickel, lead, and zinc.

Ion leaching analysis was based on water extracts analysis of mine deads, as specified in the relevant standards [1]. The analysis was performed on samples from each mine, collected at random locations and depths of each dump. Mixed material was broken up and then sifted (square mesh No. 10). Subsequently, samples were formed from sifted material, of the size corresponding to 100g of dry mass. They were put into bottles filled with water - 10 portions of water per 1 portion of dry mass by sediment weight. Next, water samples were shaken by a vibrator for 4 hours, and after a 12 hours break, again for 2 hours. After sedimentation, the liquid above the sediment was decanted and filtered through paper filters. Psychical and chemical features of the filtrate, according to appropriate standards, were finally analysed.

Three different types of water, with three different profiles, were used to perform the leaching research, which meant tightening of the recognised standards:

• distilled water, of pH app. 5.5, no chemical compounds

• water form water supply system, pH app. 7.0

• distilled water acidified with a sulphur acid, pH app. 3.5 for simulations of acid rains.
  In the course of the process metals can be transformed into ionic state, and slightly soluble (or non-soluble) compounds can be formed.

For each sample two water extracts were prepared. The results of the analysis were statistically averaged and then compared to permissible limits for inland water pollution (water purity class) and to the limits for waste water discharged to water or ground. The relevant limits can be found in standards [2]. In addition, concentration changes were calculated for specific pollution levels in water used for leaching.

Radioactivity analysis of mine deads was carried out according to relevant rules. Radiation analysis was based on guidelines used to analyse natural radioactivity of building materials [11]. Five samples from each of the dumps were analysed. In order to obtain reliable results for each dump, samples were collected at different places and dephts in a manner similar to physical chemistry analysis sample collection. Analysis was performed by means of a three-channel gamma-ray spectrometer for radiation analysis of building materials, type AZAR-82.

Radioactivity of the samples was assessed on the basis of two coefficients: f₁ and f₂. Coefficient f₁ corresponds to a measure of full human body exposure to gamma rays, caused by radioactive nuclides of geological origin, such as potassium K-40, radium Ra-226, thorium Th-228, from rock material. The formula for calculating the coefficient is complex, and for each radioisotope a different weight is used:

where:
S_k, S_ra, S_Th stand for concentrations of potassium K-40, radium Ra-226 and thorium Th-228 in Bq/kg.

The safety condition is met when coefficient f₁ is smaller then one. Safety condition is defined as boundary value for radium content in building material, for radiation of radon R_n-222:

where:
S_Ra - radium Ra-226 concentration, Bq/kg.

Safety condition is met for f₂ smaller than 185 Bq/kg.

It should be mentioned that a complete analysis of mine wastes radioactivity has never been performed, and therefore the results of such analysis cannot be found in the literature. It can be stated, however, that radioactivity of coal, and so mine wastes, is in general smaller that of other rocks [3]. It can be confirmed by research performed in Great Britain [6] and in Poland [7], [8].

RESULTS OF PHYSICAL CHEMISTRY ANALYSIS

The full scope of the results of physical chemistry analysis (leaching of ions) for samples collected at dumps of the considered mines are shown in Tables 1-3. Selected results of the analysis are presented in Figures 1-6.

The presented results prove that leaching the wastes from Ziemowit mine with standard running (natural) water led to increased conductivity due to rise in concentrations of sodium, potassium, chlorides and sulphates. It deteriorated the water quality which dropped to class III level with regards to potassium and sodium concentrations, and to class II level when manganese concentration is concerned.

Similarly, a rise in the conductivity was observed for material from Janina mine that caused the average conductivity index for washed samples to deteriorate water quality to class II. Observed potassium and sodium concentrations could be related to none of the water quality classes. In the water used for leaching Janina mine material due to a significant rise in the concentration of sulphates, a higher conductivity was observed, that corresponded to water quality class II. The same lowered water quality class was noted with regards to potassium concentration. Both manganese and sulphates concentrations were higher than the values for water quality class III.

The water leached from Jan Kanty mine waste material was of similar characteristics and the observed increase in conductivity caused sulphates concentration levels to exceed the water quality class III values.

Yet, the material from Boleslaw Śmiały mine was much less susceptible to ions leaching than the other materials, which was demonstrated by a relatively small increase in its conductivity. Such an insignificant ions leachability resulted obviously in high water quality, whose nearly all indices corresponded to water quality class I, apart from slightly increased potassium concentration that was related to water quality class II.

Despite a considerate increase in its conductivity, the water from leaching Silesia mine material was of relatively high quality, which was demonstrated by indices typical for water quality class I, apart from the one concerning potassium whose raised concentration corresponded to water quality class II. However, while leaching Siersza mine material water pH was found to drop down in comparison to the initial water value; it was contributed to the acid character of the material that corresponds to water quality class III. The other indices met the requirements for water quality class I.

Eluat resulting from leaching Brzeszcze mine material also shown lowered pH value, nevertheless, it did not result in lowering water quality class. Other pollution indices alike did not contribute to water quality class deterioration after washing, with the exemption of manganese whose increased concentration levels corresponded to water quality class III.

Determined parameters for water samples taken after leaching with distilled water are similar to the ones for running water. Low pH water (acidified) applied to the leached ions resulted in a significant reaction decrease after leaching the waste materials (deads) from Jan Kanty, Siersza and Brzeszcze mines.

Relatively high reaction - higher than 7 - after leaching from the samples colleted at Ziemowit, Janina, and Boleslaw Śmiały mines, proves strong buffering properties for this material.

Applying low reaction water for leaching proved the expected higher heavy metal contents, in relation to running water levels, in post-leaching water true. Despite a distinct increase in metal concentrations, the water quality class remained at class I level. It should be highlighted here, that for leaching the material with acidified water, solely water reaction and concentrations of heavy metals were examined. Neither the amount of sulphates, chlorides. nor other elements were determined, since their concentrations in acidified waters tend to be similar, while heavy metals become ionised and are susceptible to being leached out.

RESULTS OF RADIOACTIVITY RESEARCH

Averaged results of radioactive nuclides concentration analysis can be found in Table 4 and in Fig.7, together with results of calculations of coefficients f₁ and f₂.

a)
b)

The presented in Table 4 average values for both radionuclides concentration and f₁ and f₂ coefficients were determined for 5 sample materials collected at each deads of the concerned mines. Obtained results proved that permissible values were exceeded in none off 5 samples for each mine.

Even the highest f₁ and f₂ coefficients recorded for the material originating from dumps in Ziemowit, Janina, Silesia and Boleslaw Śmiały mines, were safely below the values of 1.0 and 185 Bq/kg, respectively (see Fig. 7).

IMPACT OF THE SOLUTE LEACHED FROM MINE DEADS ON WATER ENVIRONMENT

Based on the results of leachates analysis from eight mines it can be stated, that pollution exceeding permissible levels for surface and ground waters can occur as a result of leaching. First and foremost, it is caused by sulphates, sodium, potassium and manganese. In most analysed samples from mine dumps indicators for these chemicals are most likely to be risen. Reaction of waste materials is also important. It can have impact on increasing the leaching of non-soluble elements (including heavy metals) in neutral and basic environments. It can be confirmed by research carried by the authors, as well as by other research projects [12], [8], [10].

Obtained results cannot, however, rule out pollution of water caused by other compounds and elements, which can be a reason for water salinity - with very serious effects on the agriculture [10], [9].

Indicator values remain unaffected by the duration storage of the waste material. It should be remembered, however, that samples were collected from different places of each dump, and later the samples were mixed together. The results of sample analysis have been therefore obviously affected by the manner in which they were prepared and are therefore averaged over the entire dump for each of the mines. The results were compared with permissible concentrations values, according to the relevant standards [2] for:

• waters and waste waters discharged to soil or to surface waters,

• surface waters.

Waters from dumps can occur due to intensive rainfall, or where colliery spoils were used for embankments - also during freshets. They are characterised by waste waters parameters and, according to the authors, concentration of pollutants should be compared with appropriate permissible values for waste waters. Under such an assumption, concentrations of pollutants are lower than permissible values, with the exemption of manganese from dumps of Jan Kanty and Jaworzno mines, what may suggest the need for repeating the analysis for that mines.

However, the problem gains a different weight when pollutant indicators are compared to permissible values for surface waters. Leaching of pollutants from mine dumps causes pollutants concentrations to rise. In most cases indicators for water quality class III are not exceeded. Few cases of breaking the limits do not seem dangerous taking into account that analysis was performed in extreme conditions on not compact and artificially crumbled material. Leaching of chemicals in natural conditions is never that intensive, as it is much slower and happens periodically (precipitation). At times of great freshets leachate tends to be highly diluted.

Compacting materials when constructing the embankments may considerably decrease the unfavourable impact on the environment.

In our opinion milder requirements for using mine waste materials, defined as the biggest permissible values of pollutant indicators for waste waters discharged to water or soil, provide sufficient safety. Using such materials for earth constructions, provided that special technical protection is applied, can greatly reduce their unfavourable environmental impact.

RADIOACTIVITY OF DEADS

There are a few radioactive elements, such as potassium (K), radium (Ra) and thorium (Th), including the products of their radioactive decay, which cause gamma, alpha and beta radiation and can pollute the environment. Two radium isotopes, Ra-226 and Ra-228, present in rocks, soil and in the air, are especially dangerous for human health due to their long half-life. Effects of exposure to radon, a product of decay of radium isotopes, has focused quite an attention in Poland in the recent years. According to Plewa [4] radon unfavourably affects human health. Shall radium be absorbed by a living organism, it may cause cancer, particularly lung cancer [4]. Therefore the guidelines for analysing natural radioactivity of building materials include determination of level of the two radium isotopes.

Still, to determine radon concentration in building materials is not always possible, so when evaluating concentration of radium, first and foremost Ra-226 shall be found, as recommended by the Polish Institute for Building Technology (ITB) [11]. A combined effect of potassium, radium and thorium was also analysed. Averaged results of radioactive nuclide concentrations do not exceed following values:

for potassium K-40     750.0 Bq/kg
for radium Ra-226     111.5 Bq/kg
for thorium Th-228     87.8 Bq/kg

The highest concentrations were found in waste materials from Janina and Silesia mines, while the lowest ones in waste materials from Siersza and Jaworzno. Calculated values for f₁ and f₂ coefficients are presented in Table 4 and in Fig.7. The fall within the values:

They were found lower the permissible values. It seems, thus, reasonable to claim that mine wastes stored for some time and then used for earth constructions do not pose any radioactive threat, and do not pollute the environment.

CONCLUSIONS

The following conclusions can be drawn concerning the results of our research and its analysis:

Concentrations of pollutants in leachates in extreme conditions do not exceed permissible values for treated waste water.

• Concentrations of that chemicals in most cases do not exceed values for purity requirements for surface water class III.

• Compacting the material tight, and providing further technical treatment during construction can decrease the level of leaching.

• Coefficients f₁ and f₂, which characterise the level of materials radioactivity, are lower than the permissible values.

• Analysed materials meet the requirements for combined concentration of radioactive elements and radium Ra-226, and therefore, according to the relevant specifications, can be stored on the surface and used for building.

• Yet, the results of the analysis cannot be transferred to other areas, as they are closely related to the geological structure of the area.

REFERENCES

1. Dziennik Ustaw nr. 140, poz. 772 - Rozporzadzenie Rady Ministrów z dnia 31 grudnia 1994r. [Journal of Laws nr. 140, item 772, Decree of the Council of Ministers 31^st December 1994]. [in Polish].

2. Dziennik Ustaw nr. 116, poz. 503 - Rozporzadzenie ministra Ochrony Środowiska, Zasobów Naturalnych i Leśnictwa z dnia 31 grudnia 1994r. [Journal of Laws nr. 116, item 503, Decree of Minister of Environment Protection, Natural Resources and Forestry 16^st December 1999]. [in Polish].

3. Manning P.T.; A comparison of the radiological impacts of the coal and nuclear fuel cycles for power generation, CEGB Raport PL - GS/E/80.

4. Plewa M., Plewa S.; 1999. Radon w środowisku naturalnym i jego migracje do budynków mieszkalnych [Radon in natural environment and its migration into residential buildings], Wydawnictwo PAN, Prace Geologiczne nr. 145, Kraków. [in Polish].

5. Radolińska M,; 1959. Przekroje geologiczne przez Polskie Zagłębie Górnicze. [Geological cross-sections of Polish Coalfield]. Warszawa; [in Polish].

6. Salomon L., Tourean A., Lally A.E.; 1984. The radioactivity content of United Kingdom coal, Scci. Tot. Env. 35,403 - 415. [in English].

7. Skarżyńska K. M., Zawisza E., Jasińska M., Waligórski M.; 1993. Investigation of radioactivity of coal mining wastes, Proc. 4^th Symposium On Reclamation, Treatment and Utilization of Coal Mining Wastes. [in English].

8. Skarżyńska K.M.; 1997. Odpady powęglowe i ich zastosowanie w inzynierii lądowej i wodnej [Coal mining wastes and its usage for civil engineering], Wydawnictwo Akademii Rolniczej, Kraków.

9. Szczepańska J.; 1987. Zwałowiska odpadów górnictwa węgla kamiennego jako ogniska zanieczyśzczeń środowiska wodnego [Coal mines waste dumps as sources of water environment pollution], Zeszyty Naukowe AGH, Geologia 35/122, Kraków. [in Polish].

10. Twardowska I., Szczepańska J., Witczak S.; 1988. Wpływ odpadów górnictwa węgla kamiennego na środowisko wodne, ocena zagrożenia, prognozowanie, zapobieganiei [Impact of coal mine deads on water environment, risk assessment, forecasting, prevention], prace i studia PAN.

11. Wytyczne badania promieniotwórczości naturalnej materiałów budowlanych [Polish Institute for Building Materials (ITB), Guidelines for natural radioactivity analysis of building materials], Instrukcja w. 234/95.

12. Zapał A,; 2000. Analiza możliwości wykorzystania odpadów kopalnianych z uwzględnieniem ich wpływu na środowisko naturalne, praca doktorska [Evaluation of possible coal mine deads usage, concerning its impact on the environment, PhD dissertation], Politechnika Krakowska. [in Polish].

Responses to this article, comments are invited and should be submitted within three months of the publication of the article. If accepted for publication, they will be published in the chapter headed 'Discussions' and hyperlinked to the article.