Amine-based, hexavalent chromium reducing agents for cement
View Patent ↗Methods and compositions involving hexavalent chromate-reducing agents, particularly hydroxylamine, hydrazine, or their salts or derivatives, for use in cement compositions and cement processing.
1. A method for reducing hexavalent chromium in cementious compositions, comprising:
combining with a cement clinker, during the intergrinding of the clinker to produce cement, a reducing agent selected from the group consisting of
(A) a hydroxylamine having a structure represented by the formula
wherein R 1 and R 2 each comprise a hydrogen or C 1 -C 18 alkyl, alkene, or aryl group, or a salt or derivative of said hydroxylamine; and
(B) a hydrazine having a structure represented by the formula
wherein R 1 , R 2 , R 3 , and R 4 each comprise a hydrogen or C 1 -C 18 alkyl, alkene, or aryl group, or a salt or derivative of said hydrazine;
wherein the amount of said reducing agent is no less than 10 ppm and not greater than 5000 ppm based on weight of cement.
2. The method of claim 1 wherein said reducing agent is hydroxylamine.
3. The method of claim 2 wherein, in said hydroxylamine, R 1 is hydrogen and R 2 is an alkyl group.
4. The method of claim 3 wherein said hydroxylamine is isopropylhydroxylamine having the formula C 3 H 7 —NH—OH.
5. The method of claim 2 wherein, in said hydroxylamine, R 1 and R 2 are alkyl groups.
6. The method of claim 5 wherein said hydroxylamine is diethylhydroxylamine having the formula (C 2 H 5 ) 2 N—H.
7. The method of claim 1 wherein said reducing agent is a hydroxylamine salt.
8. The method of claim 7 wherein said hydroxylamine salt is selected from the group consisting of hydroxylamine (hydro)chloride, hydroxylamine formate, hydroxylamine phosphate, hydroxylamine sulfate, hydroxylamine nitrite, hydroxylamine acetate, hydroxylamine oxalate, and hydroxylamine nitrate.
9. The method of claim 1 wherein said hydroxylamine salt is hydroxylamine formate.
10. The method of claim 1 wherein said reducing agent is hydroxylamine sulfate.
11. The method of claim 1 wherein said reducing agent is hydrazine chloride.
12. The method of claim 1 wherein said reducing agent is a hydrazine salt selected from the group consisting of hydrazine (hydro)chloride and hydrazine sulfate.
13. The method of claim 1 wherein said reducing agent is a derivative of hydroxylamine.
14. The method of claim 13 wherein said derivative of hydroxylamine is an oxime or aldoxime.
15. The method of claim 1 wherein said reducing agent is a derivative of hydrazine.
16. The method of claim 15 wherein said derivative of hydrazine is a hydrazone.
17. The method of claim 1 further comprising combining with the cement a cement additive selected from the group consisting of an amine, alkanolamine, acrylic acid or salt thereof, glycol, glycerol, acetate salt, a phenol, chloride salt, and sugar.
18. The method of claim 1 wherein said intergrinding occurs at a temperature no less than 80° C. and no greater than 140° C.
19. A cement composition made from the method of claim 1 .
20. The composition of claim 19 further comprising a cement additive or concrete admixture selected from the group consisting of an amine, alkanolamine, acrylic acid or salt thereof, glycol, glycerol, acetate salt, a phenol, chloride salt, sugar, dispersants, lignins, air entraining surfactants, nitrite salts, and nitrate salts.
21. The composition of claim 20 further comprising an additional hexavalent chromium reducing agent.
22. The composition of claim 21 wherein said another hexavalent chromium reducing agent is selected from the group consisting of sodium bisulfite, ascorbic acid or its salt, iron sulfate, tin sulfate, and manganese sulfate.
23. A composition for adding to cement comprising: a reducing agent and, in addition to said reducing agent, a second cement additive;
said reducing agent selected from the group consisting of
(A) a hydroxylamine having a structure represented by the formula
wherein R 1 and R 2 each comprise a hydrogen or C 1 -C 18 alkyl, alkene, or aryl group, or a salt or derivative of said hydroxylamine; and
(B) a hydrazine having a structure represented by the formula
wherein R 1 , R 2 , R 3 , and R 4 each comprise a hydrogen or C 1 -C 18 alkyl, alkene, or aryl group, or a salt or derivative of said hydrazine; and,
said second cement additive being selected from the group consisting of an amine, alkanolamine, acrylic acid or salt thereof, glycol, glycerol, acetate salt, a phenol, chloride salt, and sugar.
24. The method of claim 1 further comprising combining said cement with an additional component comprising an oxygen scavenger, a metal chelating agent, or a mixture thereof.