Abstract
The generation of acid rock drainage (ARD) continues to significantly impact water resources around the globe. Passive treatment systems have been developed as lower-cost remediation alternatives to active treatment systems, but seasonality of flow, acidity, and metal concentrations present challenges for passive systems. This thesis examines the limitations of current passive treatment system options and explores the potential of a manufactured silica fiber functionalized with (3-Aminopropyl)triethoxysilane (Si+APTES) and a naturally occurring silicate mineral (clinoptilolite) as reactive substrates for passive treatment of ARD.
The first chapter is a review of passive treatment options for acid rock drainage. This review indicates reduced efficacy due to seasonal periods of increased drainage and metal concentrations that lead to mineral precipitation, surface passivation, and flow bypass. In select cases, passive treatment systems prematurely failed due to seasonal flux. Complimentary systems are needed to minimize impacts from seasonal flux of drainage and metal concentrations to improve treatment efficacy and preserve the life of a multi-component system or a downstream primary system. Multi-component systems are possible with integration of existing treatment systems and design of new treatment options to tailor treatment to site specifications.
The second chapter explores Si+APTES and clinoptilolite as potential reactive substrates for passive treatment of acid rock drainage. Column permeability experiments with silica fiber and loosely packed clinoptilolite indicate greater permeability and stability of the clinoptilolite. Batch sorption experiments with bare silica fiber, Si+APTES, and clinoptilolite in an Fe-SO4, pH 3.0 solution indicate an Fe specific sorption efficacy of Si+APTES > clinoptilolite > bare silica fiber at equivalent surface areas. Specific sorption values normalized to possible packing densities indicate greater sorption per volume for clinoptilolite. Sorption results for Si+APTES and clinoptilolite did not produce isotherms that could be described by the Langmuir or Freundlich models likely because of surface heterogeneity and precipitation reactions. Column sorption experiments under flowing conditions indicate an Fe removal efficacy of clinoptilolite > Si+APTES for permeable packing densities. Si+APTES demonstrated high specific sorption of Fe in batch sorption experiments and has potential use in low-flow, passive treatment of acid rock drainage. The balance of greater permeability, stability under flowing conditions, large surface area, microporous structure, and ion-exchange properties of clinoptilolite make these zeolite grains a better reactive substrate for passive treatment of acidic drainage in high- or low-flow conditions.