How does ammonia pressure leaching recover nickel from nickel matte?

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In the context of nickel processing, ammonia pressure leaching is a method used to treat matte to extract valuable metals.1

The process functions as follows:

Nickel Recovery: Nickel is dissolved into a solution and subsequently recovered through reduction with hydrogen under pressure.12
Cobalt Recovery: Any cobalt present in the matte is also recovered from the solution by reduction with hydrogen under pressure.2
Sulfur By-product: The sulfur contained in the matte is recovered as ammonium sulfate, which is then utilized as fertilizer.1

This method is one of several techniques, such as roasting or electrorefining, employed to refine nickel matte into high-purity products.1