Magnesium oxide for improved heavy metals removal
To improve technology for treating process water, US Bureau of Mines research has shown that magnesium oxide (MgO) has many advantages over lime or caustic soda for precipitating heavy metals. Sludge produced by MgO occupies only 0.2-0.3 times as much volume as the precipitate made using a soluble base. While a settled, lime-formed precipitate is easily resuspended, the MgO-metal hydroxide sludge becomes cemented together on standing. Settling of the metal hydroxides from a dilute suspension is more complete than precipitates formed with other bases. Virtually any metal that can be precipitated by raising the pH can be treated using MgO. A three-fold to four-fold stoichiometric excess of solid reagent is added. The mixture is reacted for five to 10 minutes. Polymer is added, and settling or filtration completes the process. Because of the greater cost of MgO compared with lime, large-scale practice of this technology will probably be limited to water containing 50 mg/L (3 gr per gal) or less of dissolved metals. For such dilute solutions, chemicals are not a large fraction of total treatment costs, so more desirable sludge properties might justify higher chemical expenses. While the MgO process is technically suitable for widespread application, the extent to which it is adopted will probably be determined by a trade-off between the greater cost of MgO compared with lime and the superior properties of the precipitates and their corresponding ultimate disposal costs.
- Research Organization:
- U.S. Bureau of Mines, Twin Cities Research Center, Minneapolis, MN
- OSTI ID:
- 5334337
- Journal Information:
- Trans. Soc. Min. Eng. AIME; (United States), Vol. 276
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
MAGNESIUM OXIDES
SOLVENT PROPERTIES
WATER TREATMENT
METALS
PRECIPITATION
WATER
DEMETALLIZATION
CALCIUM OXIDES
CEMENTING
COST
DISSOLUTION
FILTRATION
HYDROXIDES
PH VALUE
POLYMERS
REAGENTS
RESEARCH PROGRAMS
SLUDGES
SUSPENSIONS
US BUREAU OF MINES
WASTE DISPOSAL
ALKALINE EARTH METAL COMPOUNDS
CALCIUM COMPOUNDS
CHALCOGENIDES
DISPERSIONS
ELEMENTS
HYDROGEN COMPOUNDS
MAGNESIUM COMPOUNDS
MANAGEMENT
NATIONAL ORGANIZATIONS
OXIDES
OXYGEN COMPOUNDS
SEPARATION PROCESSES
US DOI
US ORGANIZATIONS
WASTE MANAGEMENT
400201* - Chemical & Physicochemical Properties