Use of majority to refer to quantity

This word should probably be used only for countable items rather than non-countable collective nouns like "garbage", but it falls into the same category as "amount" versus "the number of" when talking about countable things like people and complaints: "INFORMAL a number of things. Many people consider this use to be incorrect:

The call centre handles a huge amount of complaints every day."

The proper way to say this is:

The call centre handles a huge number of complaints every day.

The sentence you ask about should probably be:

Most of the garbage is recycled.

It's safer to stick to countable things when using majority (see Bill Franke's answer), but I don't think it's incorrect to use it the way you're proposing. From Merriam-Webster:

3 a : a number or percentage equaling more than half of a total <a majority of voters> <a two-thirds majority> b : the excess of a majority over the remainder of the total : margin <won by a majority of 10 votes> c : the greater quantity or share <the majority of the time>

Notice the example given for sense 3c, which clearly applies to an uncountable quantity. There are probably some things (like time) which are more customary for use with majority, and will perhaps grate less on finicky ears.