De or het zandvrij?

The correct Dutch article is:

de zandvrij

Rule Words ending in -ij and -erij: usually de. See the rule

How to use zandvrij

the zandvrijde zandvrij
this zandvrijdeze zandvrij
that zandvrijdie zandvrij
our zandvrijonze zandvrij
your zandvrijjouw zandvrij
every zandvrijelke zandvrij
which zandvrij?welke zandvrij?
a big zandvrij / the big zandvrijeen grote zandvrij, de grote zandvrij