Reducing agent for the soluble chromate content of cement and methods for the production thereof

Abstract

The invention relates to a reducing agent for the soluble chromate content of cement and to methods for the production thereof, which comprise concentrating an used sulfuric acid, containing iron(II) sulfate, and separating the sulfuric acid from the obtained precipitate which contains iron(II) sulfate.

1 .- 45 . (canceled)  
   
   
       46 . An iron (II) sulphate-containing reducing agent comprising green salt and an iron (II) sulphate-containing precipitate, wherein the iron (II) sulphate-containing precipitate is obtainable by a method comprising the concentration of an iron (II) sulphate-containing used sulphuric acid and the separation of the sulphuric acid from the obtained precipitate.  
   
   
       47 . The iron (II) sulphate-containing reducing agent according to  claim 46 , wherein the iron (II) sulphate-containing precipitate and the green salt are present in a ratio of 1:1 to 2:1.  
   
   
       48 . The iron (II) sulphate-containing reducing agent according to  claim 46 , characterised in that the iron (II) sulphate-containing precipitate has a titanium content of 5 to 15% by weight, based on iron, or a manganese content of 1.5 to 4% by weight, based on iron.  
   
   
       49 . The iron (II) sulphate-containing reducing agent according to  claim 46 , characterised in that the iron (II) sulphate-containing precipitate has an average crystallite size of less than 2 μm.  
   
   
       50 . The iron (II) sulphate-containing reducing agent according  claim 46 , characterised in that the iron (II) sulphate-containing precipitate has an average crystallite size of between 0.1 and 1.0 μm.  
   
   
       51 . The iron (II) sulphate-containing reducing agent according  claim 46 , characterised in that the iron (II) sulphate-containing precipitate has an average crystallite size of between 0.2 and 0.5 μm.  
   
   
       52 . The iron (II) sulphate-containing reducing agent according to  claim 46 , characterised in that the iron (II) sulphate-containing used sulphuric acid is obtained from the production of titanium dioxide according to the sulphate process.  
   
   
       53 . The iron (II) sulphate-containing reducing agent according to  claim 52 , characterised in that the iron (II) sulphate-containing used sulphuric acid has a titanium content of less than 1.5% by weight.  
   
   
       54 . The iron (II) sulphate-containing reducing agent according to  claim 46 , characterised in that the iron (II) sulphate-containing used sulphuric acid is obtained from a metal pickling process.  
   
   
       55 . The iron (II) sulphate-containing reducing agent according to  claim 46 , characterised in that the separated precipitate contains 40 to 60% by weight of iron (II) sulphate monohydrate, 3 to 10% by weight of further metal salts, 15 to 30% by weight of sulphuric acid and 10 to 13% by weight of water.  
   
   
       56 . The iron (II) sulphate-containing reducing agent according to  claim 46 , characterised in that when producing the iron (II) sulphate-containing precipitate, following separation of the sulphuric acid, reduction of the amount of sulphuric acid adhering to the separated precipitate takes place by means of further separation, partial neutralisation or neutralisation.  
   
   
       57 . The iron (II) sulphate-containing reducing agent according to  claim 56 , characterised in that reduction of the amount of sulphuric acid adhering to the separated precipitate takes place by washing with water, dilute acid, saturated FeSO 4  solution or diluted FeSO 4 -containing aqueous solutions.  
   
   
       58 . The iron (II) sulphate-containing reducing agent according to  claim 56 , characterised in that reduction of the amount of sulphuric acid adhering to the separated precipitate takes place by displacement with compressed air or by washing with steam.  
   
   
       59 . The iron (II) sulphate-containing reducing agent according to  claim 56 , characterised in that reduction of the amount of sulphuric acid adhering to the separated precipitate takes place by reacting the separated precipitate with water and metallic iron or an alkaline iron (II) compound at a temperature of greater than 60° C.  
   
   
       60 . The iron (II) sulphate-containing reducing agent according to  claim 56 , characterised in that reduction of the amount of sulphuric acid adhering to the separated precipitate takes place by means of partial neutralisation or neutralisation by adding powdered alkali compounds, selected from the group consisting of CaCO 3 , CaO, Ca(OH) 2 , MgO and/or Mg(OH) 2  or elutriations thereof.  
   
   
       61 . The iron (II) sulphate-containing reducing agent according to  claim 56  characterised in that following reduction of the amount of sulphuric acid adhering to the separated precipitate or following partial neutralisation or neutralisation of the residual acid in the separated precipitate, a defined amount of water, an aqueous saline solution or a diluted sulphuric acid is added, and granulation takes place.  
   
   
       62 . The use of the iron (II) sulphate-containing reducing agent of any one of  claims 46  to  61 , for reducing the soluble chromate content in cement.  
   
   
       63 . A method of reducing the soluble chromate content in cement comprising mixing the cement with an iron (II) sulphate-containing reducing agent comprising an iron (II) sulphate-containing precipitate, which is producible by concentrating an iron (II) sulphate-containing used sulphuric acid and separating the sulphuric acid from the obtained precipitate, the precipitate having an average crystallite size of less than 2 μm, and the precipitate having a titanium content of 5 to 15% by weight, based on iron or a manganese content of 1.5 to 4% by weight, based on iron.  
   
   
       64 . The method of  claim 63 , characterised in that 0.01 to 5.0% by weight of the iron (II) sulphate-containing precipitate is added to the cement.  
   
   
       65 . The method of  claim 63 , characterised in that the iron (II) sulphate-containing reducing agent is added to the powdered cement after milling and before or during filling in packages or bulk containers or transport containers.  
   
   
       66 . The method of  claim 65 , characterised in that after mixing with the powdered cement, the reducing effect of the iron (II) sulphate-containing reducing agent increases at least temporarily as the storage time increases.  
   
   
       67 . The method of  claim 63 , characterised in that the iron (II) sulphate-containing reducing agent is first added to the cement when it is used, in that the iron (II) sulphate-containing reducing agent is added to the cement during mixing with water, or directly before or directly after the cement is mixed with water.  
   
   
       68 . The method of  claim 67 , characterised in that the iron (II) sulphate-containing reducing agent is added in the form of a suspension or solution.  
   
   
       69 . A method of reducing the soluble chromate content in cement comprising mixing the cement with an iron (II) sulphate-containing reducing agent comprising (a) an iron (II) sulphate-containing precipitate, which is producible by concentrating an iron (II) sulphate-containing used sulphuric acid and separating the sulphuric acid from the obtained precipitate; and (b) green salt.  
   
   
       70 . The method of  claim 69 , characterised in that 0.01 to 5.0% by weight of the iron (II) sulphate-containing precipitate is added to the cement.  
   
   
       71 . The method of  claim 69 , characterised in that the iron (II) sulphate-containing reducing agent is added to the powdered cement after milling and before or during filling in packages or bulk containers or transport containers.  
   
   
       72 . The method of  claim 71 , characterised in that after mixing with the powdered cement, the reducing effect of the iron (II) sulphate-containing reducing agent increases at least temporarily as the storage time increases.  
   
   
       73 . The method of  claim 69 , characterised in that the iron (II) sulphate-containing reducing agent is first added to the cement when it is used, in that the iron (II) sulphate-containing reducing agent is added to the cement during mixing with water, or directly before or directly after the cement is mixed with water.  
   
   
       74 . The method of  claim 73 , characterised in that the iron (II) sulphate-containing reducing agent is added in the form of a suspension or solution.  
   
   
       75 . A composition comprising cement and water-soluble metal sulphates, characterised in that the composition contains 0.01 to 5.0% by weight of an iron (II) sulphate-containing precipitate, which is producible by concentrating an iron (II) sulphate-containing used sulphuric acid and separating the sulphuric acid from the obtained precipitate, the precipitate having an average crystallite size of less than 2 μm, and the precipitate having a titanium content of 5 to 15% by weight, based on iron or a manganese content of 1.5 to 4% by weight, based on iron.  
   
   
       76 . The composition of  claim 75 , further comprising green salt.  
   
   
       77 . A composition comprising cement, water and water-soluble metal sulphates, characterised in that the composition contains 0.02 to 1.5% by weight of an iron (II) sulphate-containing precipitate, based on cement, which is producible by concentrating of an iron (II) sulphate-containing used sulphuric acid and separating the sulphuric acid from the obtained precipitate, the precipitate having an average crystallite size of less than 2 μm, and the precipitate having a titanium content of 5 to 15% by weight, based on iron or a manganese content of 1.5 to 4% by weight, based on iron.  
   
   
       78 . The composition of  claim 77 , further comprising green salt.