MINERAL SCALE BUILDUP ON LINED VERUS TRADITIONAL POVLYETHYLENE PIPE MATERIALS SUBJECTED TO MINE INFLUENCED WATERS
Pezzuto, Amanda Lee
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Mine influenced waters (MIW) pose a broad range of potential environmental impacts, which often also carry financial and social consequences. MIWs are often high in solids content, and can have highly acidic or alkaline pH and high contents of metals or other problematic constituents (e.g., traces of chemicals used in minerals processing or water treatment). Acid mine drainage (AMD) is a common type of MIW characterized by low pH. Release of untreated MIWs like AMD to surface waters, for example, can lead to problems such as a sedimentation and siltation, undesirable changes in pH and/or precipitation of metals and salts, and addition of particular stressors for various aquatic organisms. As such, these waters are frequently captured and treated on-site in systems requiring extensive piping. Polyethylene (PE) pipes are popular in mining, including MIW, applications because they are chemically inert, and have relatively low costs, low density, and high flexibility. However, PE material is susceptible to abrasion. To combat this problem and offer a single pipe option for a variety of mining applications, Gerodur MPM Kunststoffverarbeitung GmbH and Co. KG.(Gerodur) has developed a novel liner for PE pipes. The liner is made of a rubber-like material that is resistant to mechanical abrasion by slurries or high-solids waters, but its susceptibility to mineral scale buildup has not been specifically evaluated. In order to evaluate scale buildup on the lined PE versus traditional PE pipe material, two studies were undertaken and are reported in this thesis. A short-term field study was conducted in the Reiche Zeche underground mine in Freiberg, Germany �" an inactive lead-zinc mine. Water quality varies considerably between different zones in this mine, but is characterized by very high dissolved solids, which is typical for AMD. For this study, the pipe materials were exposed to waters in six locations for three weeks; and were then analyzed for weight gain and scale composition. Results showed that there was only a marginal difference in the scale build up when comparing the two piping materials. In a follow-up study in the laboratory, the two pipe materials were exposed over a total of 16 weeks to three idealized AMD water qualities: an untreated AMD made to simulate the most extreme condition observed in the field study, the same AMD following passive treatment (i.e., neutral pH), and the same AMD following active treatment (i.e., slightly basic pH). Exposure was done in pipe-loop apparatuses such that samples could be subjected to different flow and sedimentation conditions (i.e., gentle mixing only on the sides of the water reservoir, gentle mixing and sedimentation on the bottom of the reservoir, and constant flow and possible sedimentation within the pipe-loop tubing itself). Results of this study indicated that factors such as water chemistry and flow velocity had significant effect on the quantity and chemistry of scale. However, there was very little difference in propensity for scale build up between the two materials. This liner was designed in an effort to resist mechanical abrasion. Because scale build up is not exacerbated by the liner, it may provide a means for uniform applications across mines with contiguous abrasive and scale prone waters. That is, it could eliminate the need to have various specialized piping materials on a site to handle these problems individually, streamlining the pumping and piping network installation and operation.
- Masters Theses