An extended soak (many days) in water containing Physan or chlorine bleach will do a pretty thorough job of disinfecting it, but E.S.’ comment about removing residues is important.
LECA is quite absorbent and the absorbed and deposited minerals go deep into the microstructure, and precipitated mineral are more difficult to redissolve than are powders. Boiling certainly isn’t enough to extract them. Probably the most effective way to do so would be a very long (weeks) soak in an excess of pure water.
I do not reuse LECA any longer for that reason, as the time, space, and minimal cost savings just don’t justify the risk to the plants.
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