Chemist here - I'd really like to see some more context, as already the English sentence sounds a bit weird to me: it's quite usual to precipitate oxalic acid by calcium (e.g by adding milk to spinach or rhubarb), but unusual to precipitate calcium by using oxalic acid (though that would work; but why go for oxalic acid if e.g. sulphuric acid also works?)
Also, a closely related sentence that would sound far more usual to me would be e.g.: "There must be (have been) pounds (tons) of oxalic acid [in that solution] for(to explain) [those [large]] calcium precipitations."
Saying that large amounts of oxalic acid are required to form a precipitate with calcium does not make sense: calcium oxalate has low solubility, so already small amounts (or more precisely: concentrations) of calcium and oxalic acid produce a precipitate.
That being said, the "pounds of" sounds quite colloquial to me, and in that case I'd translate
Da müssen Massen an Oxalsäure sein für [die|diese] Kalziumfällungen.
to precipitate => fällen oder ausfällen oder ausfallen
precipitate => Fällung oder Niederschlag oder Präzipitat (old-fashioned)
Die Lösung muss aus Massen an Oxalat und [irgendwas anderes, was ist hier unwichtig] bestehen, um solche Kalziumfällungen zu erzeugen|verursachen.
The solution must consist of ...
However, also here, I'd rather use enthalten/contain:
Die Lösung muss massenweise Oxalat enthalten, um ...
Now that we have the context, Isaac Asimov: I, Robot, p. 29
“You see,” came the cautious explanation, “all we need to do to drive him out of his rut is to increase the concentration of carbon monoxide in his vicinity. Well, back at the Station there’s a
complete analytical laboratory.”
“Naturally,” assented Powell. “It’s a Mining Station.”
“All right. There must be pounds of oxalic acid for calcium precipitations.”
“Holy space! Mike, you’re a genius.”
“So-so,” admitted Donovan, modestly. “It’s just a case of remembering that oxalic acid on heating decomposes into carbon dioxide, water, and good old carbon monoxide. College chem, you know.”
In this context, I'd translate
Dort muss es [massig|kiloweise|genug] Oxalsäure geben für die Kalziumfällungen.
Context a little bit further makes clear that kiloweise would be appropriate here as well, since they get "two three-liter jars".
(That context also tells me why they'd precipitate calcium with oxalic acid [or maybe rather ammonium oxalate]: one may want to do that in an assay for calcium quantitation because the oxalate can then conveniently be titrated with permanganate. Funny how without context the brain just picks one: even though I'm analytical chemist, I somehow assumed that the purpose of the operation would be to get calcium out of some solution, which is further used.)