Annals of Environmental Science


Annals of Environmental Science
Volume 2, December 2008, Pages 11-25, ISSN 1939-2621

Co-Precipitation of Dissolved Organic Matter by Calcium Carbonate in Pyramid Lake, Nevada

Jerry A. Leenheer and Michael M. Reddy, U.S. Geological Survey, PO Box 25046, Denver Federal Center, Denver, CO, 80225, USA

Received August 20, 2008; in final form December 17, 2008; Accepted December 30, 2008

Our previous research has demonstrated that dissolved organic matter (DOM) influences calcium carbonate mineral formation in surface and ground water. To better understand DOM mediation of carbonate precipitation and DOM co-precipitation and/or incorporation with carbonate minerals, we character-ized the content and speciation of DOM in carbonate minerals and in the lake water of Pyramid Lake, Nevada, USA. A 400-gram block of precipitated calcium carbonate from the Pyramid Lake shore was dissolved in 8 liters of 10% acetic acid. Particulate matter not dissolved by acetic acid was removed by centrifugation. DOM from the carbonate rock was fractionated into nine portions using evaporation, dialysis, resin adsorption, and selective precipitations to remove acetic acid and inorganic constituents. The calcium carbonate rock contained 0.23% DOM by weight. This DOM was enriched in polycarboxylic proteinaceous acids and hydroxy-acids in comparison with the present lake water. DOM in lake water was composed of aliphatic, alicyclic polycarboxylic acids. These compound classes were found in previous studies to inhibit calcium carbonate precipitation. DOM fractions from the carbonate rock were 14C-age dated at about 3,100 to 3,500 years before present. The mechanism of DOM co-precipitation and/or physical incorporation in the calcium carbonate is believed to be due to formation of insoluble calcium complexes with polycarboxylic proteinaceous acids and hydroxy-acids that have moderately large stability constants at the alkaline pH of the lake. DOM co-precipitation with calcium carbonate and incorpor-ation in precipitated carbonate minerals removes proteinaceous DOM, but nearly equivalent concentra-tions of neutral and acidic forms of organic nitrogen in DOM remain in solution. Calcium carbonate precipit-ation during lime softening pretreatment of drinking water may have practical applications for removal of proteinaceous disinfection by-product precursors. p>

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