I think I understand your question????"All solids from the ponds...

I think I understand your question????

"All solids from the ponds are harvested = KTMS feed salt production"

All solids from the ponds are harvested - correct, but not all are KTMS feed salt.

"I am not understanding how the process works. How can waste salt be over twice that of KTMS"

Basically, as the water evaporates from the ponds different salts will drop out of solution depending on their chemical make up. As the make up of the brine changes the solution will be transferred to the next pond where eventually the KTMS (plus others) salts drop out. Think of it as distillation by crystallization.
But all salts have to be harvested to clear the ponds but only certain ponds will contain KTMS, the rest are waste salts. Not sure where the Mg deposit.