91Pa

Protactinium

Actinidesolidblock f

One of the rarest and costliest natural elements, extracted from uranium processing waste and used to date ocean sediment and coral cores.

Atomic number	91
Standard atomic weight	231.04 g/mol ± 0.01
Group · period	f-block series · 7
Electron configuration	[Rn] 5f² 6d¹ 7s²

About Protactinium

Protactinium is what thorium becomes on the way to actinium, hence the name — the protos of actinium. It exists in uranium ore at about one part in three million, and the largest batch ever separated, 125 grams, was extracted by the UK Atomic Energy Authority in 1961 from 60 tonnes of waste at a cost of half a million pounds, which for years made it the most expensive element on any price list. It is intensely radioactive, chemically awkward and has almost no application except one that is genuinely valuable: the protactinium-231 to thorium-230 ratio in marine sediment records the strength of Atlantic overturning circulation through past climate transitions, making it one of the key proxies in palaeoceanography.

Use 231.04 g/mol in these solvers

Moles from Mass (n = m/M)

n = \frac{m}{M}

Opens with M = 231.04 g/mol already filled in

Gas Density from Molar Mass

\rho = \frac{PM}{RT}

Opens with M = 231.04 g/mol already filled in

Faraday's Law of Electrolysis (m = QM/nF)

m = \frac{Q M}{n F}

Opens with M = 231.04 g/mol already filled in

Ion Concentration as CaCO₃ Equivalent

C_{\mathrm{CaCO_3}} = C_{\mathrm{ion}} \times \frac{50.04}{\mathrm{EW}}

Opens with EW = 231.04 g/mol already filled in

Acid Feed to Reduce Alkalinity

\dot m = \frac{\Delta \mathrm{Alk} \, Q \times \frac{\mathrm{EW}}{50.04}}{p/100\%}

Opens with EW = 231.04 g/mol already filled in

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