Additive for reducing chromium (vi) ions to chromium (iii) ions

Abstract

The invention relates to an additive for reducing Cr(VI) ions to Cr(III) ions, comprising a complex of tin(II) and a carboxylic acid or a salt thereof, and to the process for the preparation thereof. It also relates to a process for preparing a material having a low chromium(VI) content. Finally, it relates to the use of said additive for reducing chromium(VI) ions to chromium(III) ions.

1 . An additive for reducing Cr(VI) ions to Cr(III) ions, comprising an aqueous solution of a complex of tin(II), and a carboxylic acid or a salt thereof.  
   
   
       2 . The additive of  claim 1 , which is in the form of a clear aqueous solution.  
   
   
       3 . The additive of  claim 1 , wherein the carboxylic acid is gluconic acid.  
   
   
       4 . The additive of  claim 1 , which further comprises a pH-adjusting agent.  
   
   
       5 . The additive of  claim 4 , wherein said pH-adjusting agent is selected from the group consisting in the alkanolamines.  
   
   
       6 . The additive of  claim 4 , wherein the pH-adjusting agent is sodium hydroxide.  
   
   
       7 . The additive of  claim 1 , further comprising an antioxidant agent selected from the group consisting in hydroquinone and the derivatives thereof, propyl gallate, (t-butyl-4-hydroxyanisole), (2,6-di-tert-butyl-p-cresol), ethyl vanillin, rosemary oil, lecithin and vitamin E.  
   
   
       8 . A process for preparing the additive of  claim 1 , including the steps of bringing a tin(II) salt into contact with carboxylic acid or a salt thereof in the presence of an appropriate amount of water.  
   
   
       9 . The process of  claim 8 , wherein the molar ratio of carboxylic acid or a salt thereof to tin(II) compound is from 0.5:1 to 5:1.  
   
   
       10 . The process of  claim 8 , wherein the tin(II) compound is selected from the group consisting in tin chloride, tin sulphate, tin fluoride and tin acetate.  
   
   
       11 . A process for preparing a material having a low chromium(VI) content, including the step of bringing the material into contact with an appropriate amount of an additive according to  claim 1 .  
   
   
       12 . The process of  claim 11 , wherein the material is a hydraulic binder.  
   
   
       13 . The process of  claim 12 , wherein the material is selected from the group consisting in cements, calcium sulphate and its hydrated forms, fly ash and slag.  
   
   
       14 . Use of an additive according to  claim 1  for preparing a material having a low chromium(VI) content.