Contact Filtration of Asbestos Fibers With Magnesium Oxide.
Pres At 109th AIME Ann Meeting Las Vegas Nev 1980 Feb; :7 pages
As part of its research on identification of asbestos fibers, the Bureau of Mines discovered a method to remove asbestos fibers from water. The process and its theory of operation is described in this report. The surface charge of amphibole minerals in potable water was negative and, in common with most other silicate minerals, the isoelectric point of amphibole asbestos fibers is in the ph range 4 to 6. Magnesia is one of the rare oxides with a high isoelectric point of about 11. The surface of magnesium oxide will be positively charged in water at ph 6 to 8, while the electric charge on amphibole asbestos fibers is negative. Because of the electrical attraction of these oppositely charged solids, it was possible to remove negatively charged asbestos fibers by percolating water that contained suspended asbestos through a porous bed of magnesium oxide particles. Scanning electron photomicrographs indicated that essentially complete removal of the fibers was accomplished. Other materials tested as contact filter media and found to be effective or partially effective were sand, calcite, carbon, diatomaceous earth, and cellulose. Acidic aluminum collected amphibole fibers but not chrysotile fibers.
Pres. At 109th AIME Ann. Meeting, Las Vegas, Nevada, Feb. 24-28, 1980, SME Preprint 80-108,