31 posts
Zinc in Raw Mix
Sir We are using Zinc Slag (a by product of Hindustan Zinc Limited ) in raw mix to maintain Fe2O3 Analysis of Zinc Slag is as :- SiO2=21 Al2O3= 11 Fe2O3=35 CaO+MgO= 2.0 SO3=4.0 gain= 3.5 Zinc=2.0 and other minor element Kindly give your view about benifit or loss due to Zinc
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537 posts
Re: Zinc in Raw Mix
Hello Dilip,
ZnO in clinker is variously reported as having the following influences on quality;-
1. >1% ZnO - retards setting time and hydration and reduces 28d strength.
2. =<1% ZnO - acts as a mineralizer during the formation of clinker (lowering Free lime and increasing alite content)
3. Increases the alite (C3S) and ferrite (C4AF) phases at the expense of aluminate (C3A) and belite (C2S).
4. Gives a darker clinker colour.
With regard to the process, ZnO may react with chloride (in the presence of alkalis and reducing conditions) to form a volatile cycle of ZnCl2 with the danger of increased buildups.
Regards,
Ted.
31 posts
537 posts
Re: Zinc in Raw Mix
Hello Dilip,
Setting time is is retarded (made longer) not 'reduced'.
There are two reasons for this;-
1.Because Zn causes less C3A to form in the clinker.This means that, for the same gypsum content, the cement paste will take proportionately longer to set
2. There is some evidence that, Zn+2 ions, released during initial hydration, react to form Zn(OH)2, or even complex salts such as calcium hydroxy-zincate, which coat the anhydrous clinker grains and retard further hydration, in a similar manner to ettringite.
For detailed information, see the following links;-
http://www.cement.org/Bookstore/download.asp?mediatypeid=1&id=12013&itemid=RD130
http://cement.sinoepsourcing.com/downLoadServlet?fileUrl=/upload/tech/SEPS_1_5_10226.pdf
(The second link is to a paper which discusses the beneficial effect of increased MgO on mitigating the negative effects of ZnO, by way of MgO-ZnO solid solution within periclase)
Regards,
Ted.