From Unofficial Stationeers Wiki
Reagent Mix is a waste ore that's output by the Recycler and furnaces. The first way reagent mix is produced is by placing an unwanted item made of multiple ingot types into the recycler; the recycler will not output each ore separately, but instead as one mass called reagent mix. Reagent mix can also be produced by the Furnace or Advanced Furnace if you try to smelt an alloy with the incorrect ratio of ores, or if the furnace is opened outside the temperature and pressure conditions of the alloy.
Reagent mix will display the ratio of ores its made of, and be the same size as its component ores. For example, if 2 copper and 8 silver are placed in a furnace and melted together, the furnace will output a stack of 10 reagent mix, each with 0.2 copper and 0.8 silver. This reagent mix will stack with itself, however it will not stack with, for example, another pile of reagent mix made of 0.4 iron and 0.6 nickel.
Reagent mix can be placed in a Centrifuge or Combustion Centrifuge to extract its component ores. This process is much faster in the combustion centrifuge, however the basic centrifuge is much less complicated.
- If reagent mix with alloys inside is passed through a centrifuge, it will be separated from the other components but will still output as reagent mix. For example, Steel will exit the centrifuge as a reagent mix that's 0.75 iron and 0.25 carbon. This will then need to be re-smelted in a furnace to get back a steel ingot. This happens for all alloys.
- A Stacker will stack reagent mixes without considering if they have the same or different compositions.