impure carbonate of sodium of natron
鹻 refers to an impure form of sodium carbonate, specifically natron, a naturally occurring mineral salt.
鹻 combines 鹵 (salt) with 兼, which likely contributes the sound. The character was created to name a specific impure salt substance.
The left side 鹵 is the salt radical, and the right side 兼 looks like a hand holding two stalks. Imagine a hand mixing impure salt crystals together: 鹻 is the impure sodium carbonate that results.
For カン, picture a can of impure salt: can -> カン, and the can is filled with the natron salt.