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Coagulant Dose

Coagulant Dose

Coagulant Dose

Good day all,

I am having trouble in trying to calculate the Aluminum (Al) wt. in the liquid alum that is dose at one of our treatment plants. The alum (Al2(SO4)3.18H2O ((48%) - Molecular wt. 666.132) daily dosing wt is 101.63 kg/d. If so would the Al (MW =27) daily dosing wt. be = 101.63*2*(27/666)= 8 kg/d? (factor of 2 is because 2 Moles of Al in Alum).

Thanks in advance.

RE: Coagulant Dose

That is correct. If you review the link below, it should be helpful:


Al2O3 is the active ingredient and that is what you are paying for when you buy aluminum sulfate. 8.5% Al2O3 is sold because that concentration has the highest freezing temperature which is practical consideration for shipping and handling.

Percent Al2O3 is a common method of quoting the strength of aluminium-based coagulants on a w/w basis. Another method of referring to concentration is to state the aluminium content, which is roughly half the Al2O3 content. For example, liquid alum of 7.5% w/w Al2O3, which is the same as 4.0% w/w aluminium (Al).

The term percent weight/weight or % w/w is similar to the previous term and is the number of kilograms of active chemical per 100 kilograms of liquid chemical. For example, liquid alum at 7.5% w/w Al2O3 has 7.5 kg of Al2O3 in solution for every 100 kg of liquid chemical delivered.

Unfortunately, General Chemical has changed hands and taken down some of the links.

RE: Coagulant Dose

Wow bmir. another great explanation by you. Although I have seen 7.5 W/W Al2O3 never thought about 7.5 kg in 100 kg of chemical!!.

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