Chemistry of inorganic compounds – Treating mixture to obtain metal containing compound – Alkaline earth metal
Patent
1998-07-28
1999-11-09
Bos, Steven
Chemistry of inorganic compounds
Treating mixture to obtain metal containing compound
Alkaline earth metal
423169, 423395, C22B 2600, C01F 1136
Patent
active
059808420
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a method for separating calcium from mixtures of metal compounds such as ores, concentrates waste products, by products and the like, and recovering the separated calcium in a useful and profitable form.
BACKGROUND OF THE INVENTION
Calcium is one of the more common elements found in both nature and many manufactured, by-product and waste substances. Its removal or recovery from such substances is often a key process step or requirement in upgrading, recovering or recycling the mixture or compound containing the calcium, or a key step in recovering the calcium in a form such as lime (CaO), which is the main calcium product of commerce.
Present methods of calcium separation from other substances are mainly based on the relative insolubility of calcium sulfate. The recovery and separation of calcium as calcium sulfate has high costs and several limitations. Not only must a source of sulfate, such as sulfuric acid, be acquired, and utilized, but the ultimate product, calcium sulfate, represents a much lesser value when compared to calcium in the form of lime, as calcium sulfate has only very limited markets.
SUMMARY OF THE INVENTION
Ores or metallurgical dusts, preferably in friable, granular or finely divided condition, are leached with nitric acid to form a mixture of calcium nitrate, other metal nitrates and some gangue materials. The nitrates, which are in solution, are removed from the leaching process, and dried at a temperature of from ambient to about 200.degree. C. to drive off the water and create a residue of solids. The solids are then heated to a temperature of from 200 to 500.degree. C. to decompose the metal nitrates to solid metal oxides, nitric oxides and oxygen in gaseous form. The gases are removed. Also left behind is calcium nitrate in solid form. The metal oxides have only low solubility or are insoluble. The solids are then leached with water, the calcium nitrate going into solution once more while the metal oxides remain as solids and are thus separated from the calcium nitrate.
If desired, the calcium nitrate can be used as a product in its then current form, or it can be heated to a temperature in excess of 550.degree. C. to decompose it by driving off the nitrogen as NO.sub.x and some of the oxygen, leaving a residue of lime (CaO).
DETAILED DESCRIPTION
The present invention not only separates the calcium from other elements with which it is commonly associated in nature and in industrial by-products, but also recovers it in a form from which it is easily recovered as the main calcium material of commerce, lime. Where desired, the calcium product that has been separated also has a substantial market.
Mixtures or compounds containing calcium and other elements are reacted with nitric acid. Nitric acid readily reacts with metals, oxides, carbonates, ferrites and other forms of natural and manmade mixtures containing calcium to form a mixture of soluble nitrates.
The metals commonly associated with calcium are magnesium, copper, iron, manganese and zinc. In many cases, all of these materials are not present simultaneously. Other metals from which calcium may be separated by the instant process are cadmium, aluminum, nickel, chromium, cobalt, silver, rare earth metals and the nuclear metals, such as uranium. Other metals whose nitrates decompose at temperatures less than 500.degree. C. can also be separated from calcium by this process.
In the practice of the present invention, these mixed nitrate solutions are concentrated and evaporated to dryness. The temperature of the dry solids is raised to between 200 and 500.degree. C. The preferred temperature for this step is about 450.degree. C. At these higher temperatures, all of the nitrates, except calcium nitrate, are decomposed to their oxides, resulting in an admixture of the respective metal oxides, along with anhydrous calcium nitrate.
The resulting admixture is leached with water to dissolve and remove the calcium nitrate, leaving the other metal oxides separated from t
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patent: 3836627 (1974-09-01), Wiensz et al.
patent: 3919395 (1975-11-01), Hauge
patent: 4871519 (1989-10-01), Zikmund et al.
Drinkard, Jr. William F.
Woerner Hans J.
Bos Steven
Drinkard Metalox, Inc.
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