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Reclaiming heavy metals from wastewater with magnesium oxide.
Khalafalla-SE; Pahlman-JE; Tallman-DN
Recycle and secondary recovery of metals: proceedings of the International Symposium on Recycle and Secondary Recovery of Metals and the Fall Extractive and Process Metallurgy Meeting, December 1-4, 1985, Fort Lauderdale, Florida. Taylor PR, Sohn HY, Jarrett N, eds. Warrendale, PA: Metallurgical Society, 1987 Feb; :227-246
The unusual electrokinetic properties of the magnesium oxide aqueous interface has been utilized to make superior filters for suspended solids and precipitants for heavy metals in wastewater streams. While the electrocapillary maxima, or points of zero charge, for most oxides and hydroxides are at a pH of about 6 (range 2.5 To 10.5), That of MgO is around ph 12.4. Lippmann's theory of electrocapillarity and the thermodynamics of surfaces would predict MgO to be positively charged at pH values below 12.4, while most other solids surfaces are negatively charged at pH values above 6. An electrokinetic attractive force between unlike charges has been found to aid in the removal of asbestos fibers and other solid particulates from water. Likewise, the basicity at the MgO surface is strong enough to precipitate many of the heavy and hazardous metals encountered in wastewater streams. Because the embryonic metal precipitates are negatively charged, many of them cement to the MgO surface, thus forming more compact sludges and much denser residues than obtained with lime, the traditional precipitant. Regeneration of the MgO filter and/or precipitant by backwashing and chemical stripping with EDTA would allow for the recovery of heavy metals in concentrated form. Since many of these heavy metals are critical and strategic, the technique can be adapted not only to recycling process water from mineral and milling waste streams, but also to reclaim their metal values.
Metallurgical-processes; Metallurgy; Waste-treatment; Metals
OP; Conference/Symposia Proceedings
Taylor-PR; Sohn-HY; Jarrett-N
Recycle and secondary recovery of metals: proceedings of the International Symposium on Recycle and Secondary Recovery of Metals and the Fall Extractive and Process Metallurgy Meeting, December 1-4, 1985, Fort Lauderdale, Florida
Page last reviewed: April 12, 2019
Content source: National Institute for Occupational Safety and Health Education and Information Division