Browsing by Subject "tasapainomallinnus"

The research subject is Waste Rock and Tailings Storage Facilities of a Finnish mine in planning. The storage facilities are considered as they will be in the operative phase of the mine. Waste rock is categorized according to its sulfur and metal content as well as buffering capabilities in to two classes; low-sulfur and high-sulfur waste rock. Waste rock is deposited in the form of piles at two different storage facilities determined by their classification. Tailings are deposited as wet slurry within embankment, where most of the tailings are partially or fully saturated with water. The aim of this study was to research contingencies in the quality assesment of seepage water produced by storage facilities. Seepage water in the mine in planning has previously been assessed with humidity cell tests, which serves as the source material for this thesis. The humidity cell tests are performed in laboratory conditions which do not respond to actual mining area conditions, thus the seepage water quality assesment cannot be done based on these tests alone. Instead they are used as source material to assess the quality of the seepage water. The effects of the conditions of humidity cell testing are the contingencies in seepage water quality assessment. The effects of the conditions studied in this thesis are temperature, rainfall, reactive mass of the waste rock and tailings as well as channeling of rain water in the waste rock storage facility. In the composition of seepage water the concentrations of sulfates and metals was examined. Humidity cell test results were fitted to the conditions in the mining area by lab-to-field scaling. The scaling correction factor or complement is based on the effects of the laboratory and mining area conditions on the quality of the seepage water that are defined in the scaling. The effect of condition factors on water quality assessment was investigated by changing the value of the scaling factor and comparing the resulting water compositions. Futhermore, the water quality estimate obtained as a result of the scaling was fed into an equilibrium modeling program to to study the precipitation reactions in the leachate and the amount of precipitation. Based on the scaling results, the sulfate and metal concentrations in the seepage water increased as the proportion of fines, reactive mass, leachable surface area, or temperature increased. If rainfall increased, the concentrations of metals and sulfates decreased. The above properties were observed for each mine wastes examined (low-sulfur and high-sulfur waste rock, tailings). The intensity of the increase or decrease in concentrations was dependent on the acidity of the seepage water of the mine waste. In the alkaline seepage water of low-sulfur waste rock and tailings, the increase in the value of the condition factor, with the exception of rainfall, led to greater changes in concentrations than in the acidic seepage water of high-sulfur waste rock. The seepage water of the high-sulfur waste rock was acidic and therefore the solubility of the metals was high and the changes in acidity didn’t significantly affect the precipitation of the substances. The final conclusion of the work was that the most significant uncertainties for the assessment of leachate quality are the grain size distribution and channeling of water in the waste rock pile, and the thickness of reactive layer in the tailings storage facility. Based on the sensitivity analysis, the effects of climate change did not significantly affect the water quality, as the simultaneous increase in temperature and precipitation offset each other's effects. It should be noted, however, that a more in-depth examination of the effects of climate change would require a seasonal examination of precipitation and temperature. In addition, variations in prolonged rainy and dry seasons should be considered, as they may have significant momentary effects on the seepage water quality.