What is appropriate to use here, who or which?
There are around 50 companies who/which deliver scanning services to private and business consumers.
NGrams charts also show that companies which do is currently more frequent than companies who do in British English, but that the opposite is the case in American English. Corpus evidence confirms these trends. The British National Corpus gives 335 returns for companies which and 177 for companies who. The Corpus of Contemporary American English gives 111 returns for companies which and 393 for companies who.
Today, both expressions are in popular use.
After a long period of vacillation, we seem to be now increasingly in favor of
companies who (do sth.)
companies which (do sth.)
The choice, though could very significantly depend on context and semantic constraints.
Funnily enough, I'd personally go for companies that do something. And borrowing @Kris' ngram links, I'd say most other people go for that too.
It largely depends on context. One would say 'A company which makes pharmaceuticals'. Just possibly you might say 'A company who make pharmaceuticals', but it doesn't sound quite right to me. But note that when you switch from 'which' to 'who' it adopts the plural form of the verb.
In your example I would use 'which'.
You would more likely say 'A company whose business is in aggregates'. But it is possible to say 'A company which has its business in aggregates'.
I worked for American companies most of my career, and I believe I have a keen ear for Americanisms, but I never noticed any difference in this instance, one side of the Atlantic versus the other.
Although companies are made up of people, companies themselves aren't people. Use "that" or "which" based on whether the company is an important part of the sentence.
He works for a company that sells insurance.
They work at the same company, which sells insurance.