re Traditional Analysis by Gravimteric & Volumetric Analysis of Cement or Clinker for Determination of SiO2,Al2O3 ,Fe2O3 & Cao & MgO

It's my pleasure, Ravi. You are quite welcome, anytime.

Ted.

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re Traditional Analysis by Gravimteric & Volumetric Analysis of Cement or Clinker for Determination of SiO2,Al2O3 ,Fe2O3 & Cao & MgO

Dear Ted

thanks for all these details

but still I request to know from you from your below comments in 1st para

"Normally hydrochloric acid is used to dissolve the clinker minerals and gypsum in the determination of free silica (insoluble residue) in clinker or cement"

Can you please elobrate some of the following points:

1.) Why HCL only select as a solution for this Silica test?

2.) which chemical reaction happen between cement , clinker or gupsum minral and HCL  so that only silica is left and other thinghs are dissolve in water?

thanks in advance for your reply.

 regards

raju verma

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re Traditional Analysis by Gravimteric & Volumetric Analysis of Cement or Clinker for Determination of SiO2,Al2O3 ,Fe2O3 & Cao & MgO

Hello Raju,

1.) Why HCL only select as a solution for this Silica test?

Because HCl is a common, relatively safe, non-oxidising acid that does not react with free SiO2. 

H2SO4 could interfere with the dissolution of CaSO4 due to the high SO4-2 ion concentration. ie  Ca+2 + SO4-2 -->CaSO4(s) which would make it more difficult to dissolve the gypsum component.

HF dissolves free silica and cannot be used.

HNO3 is a strongly oxidising acid which could attack the filter paper used in the method, causing it to fall apart.

2.) which chemical reaction happen between cement , clinker or gupsum minral and HCL  so that only silica is left and other thinghs are dissolve in water?

HCl reacts with the clinker minerals, gypsum and limestone in the cement to produce a mixture of Ca+, Cl-, SiO3-2, SO4-2, Al+3 and Fe+3 ions in solution, according to the following simplified equations;-

For C3S;-   6HCl+  + 3(CaO).SiO2 --> 3CaCl2  + H2SiO3  + 2H2O

For C2S:-   4HCl+  + 2(CaO).SiO2 --> 2CaCl2  + H2SiO3  + H2O

For C3A;-   12HCl+  + 3(CaO).Al2O3 --> 3CaCl2  + 2AlCl3  + 6H2O

For C4AF:-  20HCl+  + 4(CaO).Al2O3.Fe2O3 --> 4CaCl2  + 2AlCl3  + 2FeCl3 + 10H2O

For gypsum;- CaSO4 + 2HCl --> CaCl2 + H2SO4

For free lime; 2HCl + CaO --> CaCl2 + H2O

For limestone;- 2HCl + CaCO3 --> CaCl2 + H2O + CO2

 The only thing remaining undissolved in excess hydrochloric acid is unreacted silica from the clinker and any acid-insoluble impurites in the gypsum and limestone.  

Just as a matter of interest, the gel that is formed during the first part of the dissolution procedure is due to the H2SiO3 and H2O which are produced by the reaction of C3S and C2S with hydrochloric acid, as shown in the first two reactions above. These react to form silicic acid by the reaction;-

H2SiO3 + H2O <--> H4SiO4 (gel)

This gel finally dissolves completely upon heating with excess dilute acid.

Regards,

Ted.

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re Traditional Analysis by Gravimteric & Volumetric Analysis of Cement or Clinker for Determination of SiO2,Al2O3 ,Fe2O3 & Cao & MgO

Hello Sir

In below method Calculation of MgO is not mention & also not mention
that Filtrate is titrated using any indicator or direct titration then what
will be the end pt color changes

Complexometric determination of magnesium oxide in flyash blended cement.

A Complexometrictitration method is proposed to determine magnesium oxide in flyash blended
cement. A 0.50 g of sample was heated with hydrochloric acid for 10 min. The solution was diluted to 500 ml, and 50 ml was pipetted and heated to boiling with 2.5 ml of 5% ammonium oxalate solution. The solution was then made alkaline by ammonium hydroxide. The suspension was cooled and filtered. The filtrate was titrated by standard 0.002M EDTA solution. The concentration of MgO in sample was calculated. The flyash content of the sample was determined by British Standard method and the recovery factor (f) was calculated by the
equation of f = 100/ (99 - 0.315 x %FA). Concentration of MgO in sample was corrected by multiplying the recovery factor with concentration initially found by EDTA titration. The precision of the method is better with more time saving than the official methods.

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