Excessive free water. The drying temperature is too high.
If the zinc sulfate heptahydrate is agglomerated, there are two ways to solve it:
First, in the production process, the free product in the dry product table, if the fluidity is good, of course, the probability of agglomeration will be low. It can be dried with hot air or dried with a roller.
Second, add anti-caking agent to the product