What specific geochemical process can lead to the precipitation of minerals that clog leachate collection systems?

The specific geochemical process that can lead to the precipitation of minerals that clog leachate collection systems is the change in leachate chemistry that results in exceeding the solubility product of certain minerals, particularly calcium carbonate (CaCO3) and iron oxides/hydroxides. Leachate is a complex solution containing various dissolved ions and organic matter. Changes in pH, oxidation-reduction potential (Eh), and temperature can alter the solubility of these minerals. For example, as leachate moves through the collection system, carbon dioxide (CO2) can degas, increasing the pH. This pH increase can cause calcium ions (Ca2+) and carbonate ions (CO32-) to combine and precipitate as calcium carbonate, forming scale on the pipes and drainage media. Similarly, oxidation of dissolved iron (Fe2+) to ferric iron (Fe3+) can lead to the precipitation of iron oxides/hydroxides, especially if the leachate comes into contact with air. These mineral precipitates accumulate over time, reducing the permeability of the collection system and eventually causing clogging. These processes are exacerbated by variations in waste composition and landfill operating conditions.