SOLVING IOWA’S PHOSPHORUS PROBLEM WITH IRON MINE TAILINGS

  Sarah Liegois and Edward J. Brown    

   Most of Iowa’s lake are polluted because of their high concentration of nutrients, especially phosphorus, which leads to excessive algal growth (eutrophication). To prevent eutrophication, it is necessary to make phosphorus unavailable to algae. Ferric (Fe³⁺) and ferrous (Fe²⁺) iron are known to react with phosphate, leading to precipitates that tie up the phosphorus. Iron found in mine tailings may react with phosphorus in polluted surface water in numerous ways. The ferric iron primarily present in hematite can react directly, but it can also be reduced chemically to ferrous iron in anaerobic waters during the respiration of microorganisms present in the sediment. Then this ferrous iron can react or can be oxidized biologically to produce PO₄-fixing particulate hydrous ferric oxides (HFO) in presence of nitrates under anaerobic conditions, helping to resolve nitrogen problems also. In this study, iron (as contained in the Cuyuna mine tailings) was investigated as a treatment of excess phosphorus in Silver Lake sediments because of the numerous ways that iron reacts with phosphate.

This research was funded in part by the Roy J. Carver Charitable Trust and the Iowa Space Grant Consortium.