Total aluminium as alumina:
what do we mean?

We're frequently asked why the concentration of aluminium-based coagulants is expressed as aluminium oxide (Al₂O₃). Aluminium oxide is after all something that really can't exist in solution. The answer is that it's a long-standing convention in the industry to do so. By standardising the concentration units for aluminium-based coagulants, simpler comparisons between different products can be made. For example, if the concentration of alum sulphate solution was expressed as "% Al₂(SO₄)₃", then it would be more difficult to directly compare its concentration with a solution of polyaluminium chloride with units expressed as "%Al₂(OH)₃Cl₃". Although this method of expressing the total aluminium concentration has persisted, it would probably be more convenient still if units of "total percent aluminium" were used.

To convert "total aluminium as alumina" to "total aluminium", simply divide by 1.889. For example, a solution concentration of "10.0 weight % total aluminium as alumina" is the same as "5.29 weight % total aluminium".

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