1156 posts
Chemicals Question 1
I understand that the cement manufacturing industry is considering the use of copperas (ferrous sulphate) in the manufacture of cement to reduce chromium 6 allergy problems for the end user. My company produces the only trouble free copperas saturator on the market. Our saturator accepts crystal copperas generates a stream of aqueous ferrous sulphate solution for dosing mainly to sewage to remove phosphates or to control odour and septicity in sewers and sewage works. I am interested to understand the mechanisms underlieing the use of copperas for cement production.
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1156 posts
Re: Chemicals
You are right that cement companies are considering the addition of ferrous sulphate to their cement in order to meet the stricter limits on hexavalent chromium that are being introduced. The application involves adding solid ferrous sulphate to the cement either at the milling or packing stage and relying on this to reduce any hexavalent chromium present in the cement. The industry knows that this solution has its limitations, not least being that the activity of the solid ferrous sulphate will deterioratr with time and this will confer a "shelf-life" to cement treated in this way to meet the directive.
1156 posts
Chemicals Question 2
We are using synthesized calcium sulphate anhydrite from a nearby aluminium plant. This calcium sulphate (96 per cent purity) is fine in form and free from moisture. In addition to CaSO42. Can Calcium sulphate be used as an alternative retarder for the Natural Gypsum? Your expert opinion on the solubility of this synthetic calcium sulphate anhydrite is appreciated.
1156 posts
Re: Chemicals
The solubility of anhydrite varies dependent on the temperature history to which it has been subjected. However, I am sure this will be a good material to use as a set-controlling additive in your cement. You may need to use it in combination with your natural gypsum or you may be able to replace your natural gypsum with 100 per cent of this material. The only way to find out will be to conduct trials with the synthetic CaSO4.