The most common and most likely answer to this crossword clue is the 6 letter word BORATE
B
O
R
A
T
E
More clues leading to the result BORATE
Buddy explains!

The straight part
We know that "Salt" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case salt = borate.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does BORATE mean?
BORATE noun- The oxyanion BO33- or any of several more complex derivatives
- A salt or ester formed by the combination of boric acid with a base or positive radical