The beneficial use of coal fly ash in reactive mine tailings and acid mine drainage management.

摘要

The thesis focuses on the mechanisms, environmental benefits and methods of coal fly ash application in reactive mine tailings and acid mine drainage (AMD) management. The tailings are from the Musselwhite Mine the fly ashes are from the Nanticoke and Atikokan Generating Stations and the AMD is from the Sudbury Mine.The kinetic column leaching tests on the Nanticoke and Atikokan fly ashes with the AMD permeation show that the interactions of both materials will result in hydraulic conductivity decreases of the coal fly ashes. An analytical model is developed to simulate the decreases and to enhance understanding of scientific principles. The model is a combination of the Kozeny-Carman equation, speciation calculation, specific surface area estimation and linear interpolation for the void ratio estimation. There is good agreement between the results of experiments and modelling.Furthermore, kinetic column leaching tests show the Atikokan fly ash can significantly reduce the metal concentrations in the AMD. The decreases of metal concentrations are resulted from precipitation, ion exchange and adsorption. The adsorption of metals (Mn2+, Ni2+ and Zn2+) onto calcium silicate hydrate is simulated based on principles of chemical equilibrium, speciation, and electrical double layer.A pilot study is implemented on the Musselwhite Mine site to verify the laboratory results and assess the feasibility of using coal fly ash for mine closure in the future. Four testing tanks were installed to monitor the long-term performance of using coal fly ash for tailings oxidation prevention. Tank A contains the tailings only, and is used as a control test. In Tank B, 10% Atikokan ash and 90% Musselwhite tailings are placed layer by layer. Tank C and D contain the ash-tailings mixtures with the mass ratios of 10:90 and 15:85, respectively. The real time monitoring includes surface conditions temperature and water content distribution in the tanks pH, electrical conductivity and elemental concentrations of the pore fluid. The data obtained between year 2006 and 2008 are presented along with a preliminary analysis. The pilot study provides valuable information for future engineering practice.The use of coal fly ash in tailings treatment may reduce the usage of lime. Because some coal fly ashes are alkaline in nature, they have considerable neutralization capacities to prevent or mitigate tailings oxidation. A direct benefit of reducing lime usage is the reduction of green house gas generation during lime production.Key Words: coal fly ash, reactive mine tailings, acid mine drainage, greenhouse gas, kinetic column leaching test, ettringite, calcium silicate hydrate, hydraulic conductivity, metal stabilization, adsorption, pilot study.