Recycling is the
technology of recapturing used materials to use again. The
concept of recycling has been around since an early prehuman used the
same stick to clobber an antelope as (s)he used to cook it in the
fire.
In normal operations, all used-up items will be
partially recycled. The fraction recycled will be the percent of
total recycling development times the amount of effort spent recycling
that material. For example, we (in the real world) aren't
particularly much better at recycling gold than we are at recycling
steel. We effectively recycle a greater fraction of gold,
however, because it's financially worthwhile to work far harder with
gold. Similarly, for those materials which are in shortest supply
in a given situation, spending more effort on recycling is
sensible. Effort spent recycling a material contributes as
experimental effort toward improving that recycling development.
Matter-Energy
Conversion allows 100% effective recycling (although it may not be
financially worthwhile to use it).
The fraction of a used-up item's materials which are
not recycled are assumed to be landfilled or otherwise lost into the
environment. This material does not simply cease to exist, but it
will be very difficult to reclaim. As such, this material is not
simply added to the top of the mineral concentrations on a body, but
essentially added to the bottom. The total reserves of that
material on the planet/etc. are increased by the appropriate amount,
but the difficulty of extraction is increased such that the difficulty
of mining the next kiloton of material remains unchanged. It can
be thought of as adding that amount of material at the bottom of a deep
mine shaft, where it's most difficult to reclaim.