Additives for Suppressing Tungsten Leachability
The leachability of tungsten in an aqueous medium may be suppressed by combining tungsten metal with a metal oxide or metal salt that will form an insoluble tungsten-containing compound when the mixture is brought into contact with an aqueous medium. The additive is preferably present in an amount from about 1 weight percent (wt. %) to about 10 weight percent of the tungsten of the tungsten. Preferred additives are lead oxide and calcium sulfate.
1 . A method of suppressing the leachability of tungsten, comprising:
combining tungsten metal with a metal oxide or metal salt, contacting the combination with an aqueous medium whereby an insoluble tungsten-containing compound is formed.
2 . The method of claim 1 wherein the metal oxide is lead oxide.
3 . The method of claim 1 wherein the metal salt is lead nitrate or calcium sulfate.
4 . The method of claim 1 wherein the insoluble tungsten-containing compound is lead tungstate or calcium tungstate.
5 . The method of claim 1 wherein the pH of the aqueous medium is from about 4 to about 9.
6 . The method of claim 1 wherein the amount of the metal oxide or metal salt is from about 1 weight percent to about 10 weight percent of the tungsten.
7 . The method of claim 1 wherein the amount of the metal oxide or metal salt is from about 1 weight percent to about 2 weight percent of the tungsten.
8 . A powder mixture, comprising: a mixture of tungsten metal and a metal oxide or metal salt wherein the metal oxide or metal salt induces the formation of an insoluble tungsten-containing compound when the mixture is contacted with an aqueous medium.
9 . The mixture of claim 8 wherein the metal oxide is lead oxide.
10 . The mixture of claim 8 wherein the metal salt is lead nitrate or calcium sulfate.
11 . The mixture of claim 8 wherein the insoluble tungsten-containing compound is lead tungstate or calcium tungstate.
12 . The mixture of claim 8 wherein the pH of the aqueous medium is from about 4 to about 9.
13 . The mixture of claim 8 wherein the amount of the metal oxide or metal salt is from about 1 weight percent to about 10 weight percent of the tungsten.
14 . The mixture of claim 8 wherein the amount of the metal oxide or metal salt is from about 1 weight percent to about 2 weight percent of the tungsten.
15 . A tungsten-containing article, comprising: tungsten metal and a metal oxide or metal salt wherein the metal oxide or metal salt induces the formation of an insoluble tungsten-containing compound when the article is contacted with an aqueous medium.
16 . The article of claim 15 wherein the amount of the metal oxide or metal salt is from about 1 weight percent to about 10 weight percent of the tungsten.
17 . The article of claim 15 wherein the amount of the metal oxide or metal salt is from about 1 weight percent to about 2 weight percent of the tungsten.
18 . The article of claim 15 wherein the metal oxide is lead oxide.
19 . The article of claim 15 wherein the metal salt is lead nitrate or calcium sulfate.
20 . The article of claim 16 wherein the metal oxide is lead oxide.