Teachers can save and recycle alum crystals and solutions. To do this, place all unwanted crystals and solutions in a large beaker and heat it to about 80 degrees C.
The hot solution will need to be stirred for quite a while to dissolve any large alum crystals. Filter the hot solution through filter paper and allow the filtrate to cool.
Solid alum will then deposit on the bottom of the beaker and may be collected by filtration.
Some teachers may not have the equipment or facilities to recycle alum. It may be possible to convince a generous colleague in the high school to help with the recycling.