Cleaning your bathroom with soil science

I was very proud of myself in the weekend. Some time after renovating our bathrooms at home, we found brownish water stains on the otherwise glossy white acrylic vanity tops. Not a good look. Guessing that these were some sort of iron oxide precipitate, I suggested that my wife try a mixture of lemon juice and baking soda on the stain. As you might expect, this was based on a re-interpretation of a commonly used method for selectively dissolving iron oxides in soils, the DCB (dithionite-citrate-bicarbonate) method. The basis of the method was first published by Mehra and Jackson in 1960; I'm more familiar with the method instructions in Loeppert and Inskeep (1996).

To dissolve iron oxides efficiently your [cleaning] solutions needs to have three key properties:

1. something to reduce Fe³⁺ to Fe²⁺
2. something to form a complex with Fe²⁺
3. a buffer to keep the pH high enough.

In Mehra and Jackson's method 1.=dithionite, 2.=citrate, and 3.=sodium bicarbonate. Fortunately this can be approximated using household ingredients. In the lemon juice / baking soda system, the reducing agent (1.) is the ascorbic acid (vitamin C!) in the lemon juice (dithionite is kind of nasty to handle anyway); the lemon juice is also a good source of citric acid (2.). Baking soda is sodium bicarbonate (3.), so no substitution problems there. We applied the mixture to the stain, left it for a moment, and scrubbed with an old toothbrush. Better than abrasive cleaners on an acrylic vanity top, and the stain was completely removed!

I've used adaptations of this method successfully before to remove iron stains from kettles (half a lemon and a teaspoonful of baking soda in the kettle; fill with water, boil, discard, and rinse) and toilets (similar to kettles, but you'll need to add hot water to the bowl...)

 

Literature

Loeppert, R.H. & Inskeep, W.H. (1996). Iron. In Methods of Soil Analysis. Part 3 - Chemical Methods. (Eds D.L. Sparks, A.L. Page, P.A. Helmke, R.H. Loeppert, P.N. Soltanpour, M.A. Tabatabai, C.T. Johnston and M.E. Sumner) pp. 639-664. (Soil Science Society of America: Madison, WI, USA).

Mehra, O.P. & Jackson, M.L. (1960). Iron oxide removal from soils and clays by a dithionite-citrate system buffered with sodium bicarbonate. In Clays and Clay Minerals, Proc. 7^th Natl. Congr.; Pergamon, London.

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P.S. If you're sensitive about such things, it's usually me who cleans the bathrooms in our house. I was redecorating the bedroom at the time...

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Soil image from www.agric.wa.gov.au