Both these terms are used in relation to glass recycling and without context it is difficult to say which might fit better.

molturar⇒ vtr (moler granos) grind⇒, mill⇒ vtr
https://www.wordreference.com/es/en/translation.asp?spen=mol...

International Innovative Technologies Ltd. (IIT) has secured an order for a milling system utilizing its patented fine grinding technology for waste glass recycling.
http://archive.glassonline.com/site/news/channelname/Recycli...


Grant Thornton described the government's policy towards recycling as “carbon blind”, and that energy-intensive processes such as glass grinding produced more emissions than if the glass was just disposed of.
https://www.letsrecycle.com/news/latest-news/wrap-defends-us...

The use of recycled glass as a substitute for cement/fly ash would prevent air pollution from Portland cement production, improve community recycling programs (particularly for glass), provide economic benefit to communities by limiting costs for cement products (particularly in rural areas) and potentially provide new jobs through increased glass recycling, glass cleaning, and glass milling.
https://cfpub.epa.gov/ncer_abstracts/index.cfm/fuseaction/di...